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Title: Texas Fossils: An Amateur Collector's Handbook

Author: William Henry Matthews

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Most recently updated: October 23, 2024

Language: English

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*** START OF THE PROJECT GUTENBERG EBOOK TEXAS FOSSILS:
AN AMATEUR COLLECTOR'S HANDBOOK ***

BUREAU OF ECONOMIC GEOLOGY
The University of Texas at Austin
Austin, Texas 78712
John T. Lonsdale, Director

Guidebook 2

TEXAS FOSSILS:
An Amateur Collector’s Handbook

By
William H. Matthews III

November 1960
Second Printing, July 1963
Third Printing, August 1967
Fourth Printing, June 1971
Fifth Printing, November 1973
Sixth Printing, April 1976
Seventh Printing, November 1978
Eighth Printing, September 1981
Ninth Printing, August 1984

iii

Contents

Page
Introduction 1
What are fossils? 3
The study of fossils 4
Paleobotany 4
Invertebrate paleontology 4
Vertebrate paleontology 4
Micropaleontology 4
Preservation of fossils 5
Requirements of fossilization 5
Missing pages in the record 5
Different kinds of fossil preservation 7
Original soft parts of organisms 7
Original hard parts of organisms 7
Calcareous remains 10
Phosphatic remains 10
Siliceous remains 10
Chitinous remains 10
Altered hard parts of organisms 10
Carbonization 10
Petrifaction or permineralization 10
Replacement or mineralization 10
Replacement by calcareous material 11
Replacement by siliceous material 11
Replacement by iron compounds 11
Traces of organisms 11
Molds and casts 11

Tracks, trails, and burrows 14
Coprolites 14
Gastroliths 14
Pseudofossils 14
Dendrites 14
Slickensides 16
Concretions 16
Where and how to collect fossils 17
Collecting equipment 17
Where to look 19
How to collect 20
Cleaning and preparation of fossils 21
How fossils are named 21
The science of classification 21
The units of classification 22
Identification of fossils 23
Use of identification keys 23
Identification key to main types of invertebrate fossils 26
List of Texas colleges offering geology courses 27
Cataloging the collection 31
How fossils are used 31
Geologic history 33
Geologic column and time scale 33
The geology of Texas 34
Physiography 35
Trans-Pecos region 35
Texas Plains 35
High Plains 35
North-central Plains 37
Edwards Plateau 37
Grand Prairie 37
Llano uplift 37
Gulf Coastal Plain 37
Geology 37
Precambrian rocks 40
Paleozoic rocks 40
Cambrian 40
Ordovician 40

Silurian 40
Devonian 40
Mississippian 41
Pennsylvanian 41
Permian 41
Mesozoic rocks 42
Triassic 42
Jurassic 42
Cretaceous 42
Cenozoic rocks 43
Tertiary 43
Quaternary 43
Main types of fossils 44
Plant fossils 44
Classification of the plant kingdom 44
Division Thallophyta 44
Division Bryophyta 44
Division Tracheophyta 44
Animal fossils 48
Phylum Protozoa 48
Class Sarcodina 48
Order Foraminifera 48
Order Radiolaria 48
Phylum Porifera 49
Phylum Coelenterata 49
Class Anthozoa 49
Subclass Zoantharia 50
Order Rugosa 50
Order Scleractinia 50
Order Tabulata 50
Phylum Bryozoa 50
Phylum Brachiopoda 54
Class Inarticulata 54
Class Articulata 56
Phylum Mollusca 56
Class Gastropoda 59
Class Pelecypoda 59
Class Cephalopoda 66

Subclass Nautiloidea 66
Subclass Ammonoidea 75
Subclass Coleoidea 78
Order Belemnoidea 78
Phylum Annelida 78
Phylum Arthropoda 78
Subphylum Trilobitomorpha 78
Class Trilobita 78
Subphylum Crustacea 80
Class Ostracoda 80
Phylum Echinodermata 80
Subphylum Pelmatozoa 81
Class Cystoidea 81
Class Blastoidea 81
Class Crinoidea 81
Subphylum Eleutherozoa 82
Class Asterozoa 82
Subclass Asteroidea 82
Subclass Ophiuroidea 82
Class Echinozoa 82
Subclass Echinoidea 82
Subclass Holothuroidea 85
Phylum Chordata 85
Subphylum Hemichordata 85
Class Graptolithina 85
Subphylum Vertebrata 86
Superclass Pisces 87
Class Agnatha 87
Class Placodermi 87
Class Chondrichthyes 87
Class Osteichthyes 87
Superclass Tetrapoda 89
Class Amphibia 89
Class Reptilia 89
Cotylosaurs 89
Turtles 89
Pelycosaurs 89
Therapsids 89

Ichthyosaurs 95
Mosasaurs 95
Plesiosaurs 95
Phytosaurs 95
Crocodiles and alligators 95
Pterosaurs 95
Dinosaurs 95
Order Saurischia 97
Suborder Theropoda 97
Suborder Sauropoda 97
Order Ornithischia 97
Suborder Ornithopoda 97
Suborder Stegosauria 97
Suborder Ankylosauria 97
Suborder Ceratopsia 100
Class Aves 100
Class Mammalia 100
Subclass Allotheria 100
Subclass Theria 100
Order Edentata 100
Order Carnivora 102
Order Pantodonta 102
Order Dinocerata 102
Order Proboscidea 102
Order Perissodactyla 104
Horses 104
Titanotheres 104
Chalicotheres 106
Rhinoceroses 106
Order Artiodactyla 106
Entelodonts 106
Camels 106
Books about fossils 108
General works 108
Nontechnical and juvenile 108
Collecting helps 108
Reference works 109
Selected references on Texas fossils 109

Glossary 111
Index 115

Illustrations

Figures— Page
1. Sketch of a coprolite—fossilized animal excrement 14
2. Sketch of a gastrolith—the gizzard stone of an ancient reptile 14
3. Dendrites—a typical pseudofossil 14
4. Types of symmetry in a fossil coral 24
5. Bilateral symmetry in fossil brachiopod 24
6. A brachiopod showing specimen number and accompanying label 31
7. Two types of micropaleontological slides 32
8. Typical Pennsylvanian crinoidal limestone 41
9. Typical Texas Foraminifera 49
10. Typical radiolarians 49
11. Morphology and principal parts of corals 50
12. Two types of bryozoans 50
13. Morphology and principal parts of articulate brachiopods 54
14. Lingula, a typical inarticulate brachiopod 56
15. Kingena wacoensis, a common Cretaceous brachiopod 56
16. Morphology and principal parts of gastropod shells 60
17. Morphology and principal parts of a typical pelecypod shell 65
18. Morphology and principal parts of the pearly nautilus 75
19. Characteristic features of the various types of cephalopod sutures 75
20. Types of typical fossil annelid worms 78
21. Morphology and principal parts of trilobites 80
22. Two extinct attached echinoderms, Pentremites and Caryocrinites 81
23. Typical modern crinoid, or “sea lily,” showing principal parts 81
24. Graptolites 86
25. Sketches of mastodon and mammoth teeth 104
26. Two views of a typical fossil horse tooth 104

Plates— Page
1. Geologic time scale Frontispiece
2. Types of fossil preservation 8
3. Silicified brachiopods dissolved from Permian limestones of the
Glass Mountains, Brewster County, Texas
12
4. Dinosaur tracks in limestone in bed of Paluxy Creek near Glen
Rose, Somervell County, Texas
15
5. Fossil collecting equipment 18
6-8. Fossil identification charts 28-30
9. Physiographic map of Texas 36
10. Geologic map of Texas 38-39
11. Geologic range of the major groups of plants and animals 45
12. Fossil plants—thallophytes and tracheophytes 46
13. Fossil plants—tracheophytes 47
14. Paleozoic sponges and sponge spicules 51
15. Pennsylvanian corals 52
16. Cretaceous and Tertiary corals 53
17. Pennsylvanian bryozoans and Cambrian and Mississippian
brachiopods
55
18, 19. Pennsylvanian brachiopods 57, 58
20. Pennsylvanian gastropods 61
21. Pennsylvanian and Cretaceous gastropods 62
22, 23. Tertiary gastropods 63, 64
24. Pennsylvanian pelecypods 67
25-28. Cretaceous pelecypods 68-71
29-31. Tertiary pelecypods 72-74
32. Pennsylvanian and Cretaceous cephalopods 76
33. Cretaceous cephalopods 77
34. Fossil arthropods 79
35. Fossil starfishes, crinoids, and holothurian sclerites 83
36. Cretaceous echinoids 84
37. Primitive armored fish, shark teeth, and conodonts 88
38. Comparison of the dinosaurs 90
39. Comparison of Mesozoic flying and swimming reptiles 91
40. Pelycosaur, cotylosaur, and a primitive amphibian 92

41. Swimming reptiles 93
42. Phytosaur and flying dinosaurs 94
43. Skull of Phobosuchus, from Cretaceous of Trans-Pecos Texas 96
44. Saurischian dinosaurs 98
45. Ornithischian dinosaurs 99
46, 47. Cenozoic mammals 101, 103
48. Tertiary mammals 105
49. Cenozoic mammals 107

viii
Plate 1
GEOLOGIC TIME SCALE

ERA
PERIOD
EPOCH
CHARACTERISTIC LIFE
CENOZOIC “Recent Life”
QUATERNARY 1 MILLION YEARS
Recent
Pleistocene
TERTIARY 64 MILLION YEARS
Pliocene
Miocene
Oligocene
Eocene
Paleocene
MESOZOIC “Middle Life”
CRETACEOUS 70 MILLION YEARS
JURASSIC 45 MILLION YEARS
TRIASSIC 50 MILLION YEARS
PALEOZOIC “Ancient Life”
PERMIAN 55 MILLION YEARS
CARBONIFEROUS
PENNSYLVANIAN 30 MILLION YEARS
MISSISSIPPIAN 35 MILLION YEARS
DEVONIAN 55 MILLION YEARS
SILURIAN 20 MILLION YEARS
ORDOVICIAN 75 MILLION YEARS
CAMBRIAN 100 MILLION YEARS
PRECAMBRIAN ERAS
PROTEROZOIC ERA
ARCHEOZOIC ERA
APPROXIMATE AGE OF THE EARTH MORE THAN 3 BILLION 300 MILLION YEARS

1

Texas Fossils
An Amateur Collector’s Handbook
[1]
William H. Matthews III

INTRODUCTION

Almost everyone has seen the fossilized remains of prehistoric plants or
animals. These might have been the skeleton of a gigantic dinosaur, the
petrified trunk of an ancient tree, or the shells of snails or oysters that lived
in the great seas that covered Texas millions of years ago.

Each year more and more people are learning that these fossils are more than
mere curiosities. Instead, they are realizing that a good collection of fossils
provides much information about the early history of our earth, and that
fossil collecting can be a most enjoyable, fascinating, and rewarding hobby.
It is for these people that Texas Fossils was written.

This publication is primarily an amateur collector’s handbook and as such
offers many suggestions and aids to those who would pursue the hobby of
fossil collecting. It tells, for example, what fossils are, where and how to
collect them, and how they are used. Suggestions are made as to how the
specimens may be identified and catalogued, and there are discussions and
illustrations of the main types of plant and animal fossils. Included also is a
simplified geologic map of Texas and a brief review of the geology of the
State.

Texas Fossils is not a comprehensive study of the paleontology of Texas.
Rather, it deals primarily with the more common species that the average
collector is likely to find. These fossils are illustrated in the plates and
figures, and these illustrations should be of some help in identifying the
specimens in one’s collection. Included for completeness, however, are
sketches and descriptions of some of the more rare and unusual fossils, and,

for general interest, there are illustrations and descriptions of many of the
extinct reptiles and mammals that once inhabited this State.

In addition, a group of selected references has been included for the reader
who wishes to know more about earth history and paleontology. Many of
these publications provide references of a more technical nature for the more
advanced or serious collector, and some of them list excellent collecting
localities.

A minimum of technical terminology has been used, but terms not
commonly found in dictionaries, or which have not been explained in the
text, are defined in the glossary (pp. 111-114).

Many people have helped in the planning, preparation, and completion of
Texas Fossils, and their help is gratefully acknowledged: Dr. Keith Young,
The University of Texas; Dr. Harold Beaver, Baylor University; and
Professor Jack Boon, Arlington State College, offered helpful suggestions
and information on Cretaceous fossils; Professors Richmond L. Bronaugh,
Baylor University, and Jack T. Hughes, West Texas State College, provided
information on vertebrate collecting localities; Professor Fred Smith, Texas
A&M College, supplied data on Tertiary collecting localities and fossils
which were used in illustrations; Dr. Saul Aronow and Professor Darrell
Davis, Lamar State College of Technology; Dr. Jules DuBar, University of
Houston; and Dr. Samuel P. Ellison, The University of Texas, made valuable
suggestions which have been incorporated into the manuscript.

Special thanks are due Drs. John T. Lonsdale, L. F. Brown, Jr., and Peter U.
Rodda, Bureau of Economic Geology, who critically read the 2
manuscript and contributed greatly to the presentation of the material;
Dr. John A. Wilson, The University of Texas, who read the section on
vertebrate fossils and made invaluable suggestions and criticisms; Miss
Josephine Casey, who edited the manuscript; and Mr. J. W. Macon, who
prepared the maps and charts.

Thanks are due also to Dr. G. A. Cooper, United States National Museum,
who prepared Plate 3 especially for this publication, and to R. T. Bird and
the American Museum of Natural History for photographs used in Plates 4
and 43. Plates 38 and 39 were provided through the courtesy of Dr. J. W.

Dixon, Jr., and the Geology Department of Baylor University. The other
photographs were prepared by the writer. To Sarah Louise Wilson, Lamar
State College of Technology, the writer gratefully acknowledges her tireless
and painstaking efforts in preparing the many fine drawings which make up
the balance of the illustrations.

3

WHAT ARE FOSSILS?

Fossils are the remains or evidence of ancient plants or animals that have
been preserved in the rocks of the earth’s crust. Most fossils represent the
preservable hard parts of some prehistoric organism that once lived in the
area in which the remains were collected.

The word fossil is derived from the Latin word fossilis, meaning “dug up,”
and for many years any unusual object dug out of the ground was considered
to be a “fossil.” For this reason some of the earlier books dealing with fossils
include discussions of rocks, minerals, and other inorganic objects.

There is much evidence to indicate that man has been interested in fossils
since the very earliest times, and fossil shells, bones, and teeth have been
found associated with the remains of primitive and prehistoric men. It is
quite possible that the owners of these objects believed that they possessed
supernatural powers, such as healing properties or the ability to remove
curses.

During the earliest periods of recorded history, certain Greek scholars found
the remains of fish and sea shells in desert and mountainous regions. These
men were greatly puzzled by the occurrence of these objects at such great
distances from the sea, and some of them devoted considerable time to an
explanation of their presence.

In 450 B.C., Herodotus noticed fossils in the Egyptian desert and correctly
concluded that the Mediterranean Sea had once been in that area.

Aristotle in 400 B.C. stated that fossils were organic in origin but that they
were embedded in the rocks as a result of mysterious plastic forces at work
within the earth. One of his students, Theophrastus (about 350 B.C.), also
believed that fossils represented some form of life but thought that they had
developed from seeds or eggs that had been planted in the rocks.

Strabo (about 63 B.C. to A.D. 20) was another important Greek scholar who
attempted to explain the presence of fossils. He noted the occurrence of
marine fossils well above sea level and correctly inferred that the rocks
containing them had been subjected to considerable elevation.

During the “Dark Ages” fossils were alternately explained as freaks of
nature, the remains of attempts at special creation, and devices of the devil
which had been placed in the rocks to lead men astray. These superstitious
beliefs and the opposition from religious authorities hindered the study of
fossils for hundreds of years.

In approximately the middle of the fifteenth century the true origin of fossils
was generally accepted, and they were considered to be the remains of
prehistoric organisms which had been preserved in the earth’s crust. With the
definite recognition of fossils as organic remains, many of the more
primitive theories were discarded for one just as impractical—these remains
were considered remnants of the Great Flood as recorded in the Scriptures.
The resulting controversy between scientists and theologians lasted for about
300 years.

During the Renaissance several of the early natural scientists concerned
themselves with investigations of fossils. Noteworthy among these was
Leonardo da Vinci, the famous Italian artist, naturalist, and engineer.
Leonardo insisted that the Flood could not be responsible for all fossils nor
for their occurrence in the highest mountains. He reaffirmed the belief that
fossils were indisputable evidence of ancient life, and that the sea had once
covered northern Italy. Leonardo explained that the remains of the animals
that had inhabited this ancient body of water were buried in the sediments of
the sea floor, and that at some later date in earth history this ocean 4
bottom was elevated well above sea level to form the Italian peninsula.

In the late eighteenth and early nineteenth centuries the study of fossils
became firmly established as a science, and since that time fossils have
become increasingly important to the geologist.

THE STUDY OF FOSSILS

The study of fossils is called paleontology (Greek palaios, ancient; ontos, a
being; logos, word or discourse). Information gathered with the help of
paleontology has greatly increased the knowledge of ancient plants and
animals and of the world in which they lived.

Fossils represent the remains of such great numbers and various types of
organisms that paleontologists have found it helpful to establish four main
divisions within their science.

Paleobotany

Paleobotany deals with the study of fossil plants and the record of the
changes which they have undergone.

Invertebrate Paleontology

This is the study of fossil animals without a backbone or spinal column.
These include such forms as fossil protozoans (tiny one-celled animals),
snails, clams, starfish, and worms, and usually represent the remains of
animals that lived in prehistoric seas.

Because invertebrate remains are the most common fossils in Texas, this
book is devoted largely to the discussion of invertebrate fossils and their
method of collection.

Vertebrate Paleontology

The vertebrate paleontologist studies the fossils of animals which possessed
a backbone or spinal column. The remains of fish, amphibians, reptiles,
birds, and mammals are typical vertebrate fossils.

Micropaleontology

Micropaleontology is the study of fossils that are so small that they are best
studied under a microscope. These tiny remains are called microfossils and
usually represent the shells or fragments of minute plants or animals.
Because of their small size, microfossils can be brought out of wells without
being damaged by the mechanics of drilling or coring. For this reason
microfossils are particularly valuable to the petroleum geologist who uses
them to identify rock formations thousands of feet below the surface.

5

PRESERVATION OF FOSSILS

The majority of fossils are found in marine sedimentary rocks. These are
rocks that were formed when salt-water sediments, such as limy muds,
sands, or shell beds, were compressed and cemented together to form rocks.
Only rarely do fossils occur in igneous and metamorphic rocks. The igneous
rocks were once hot and molten and had no life in them, and metamorphic
rocks have been so greatly changed or distorted that any fossils that were
present in the original rock have usually been destroyed or so altered as to be
of little use to the paleontologist.

But even in the sedimentary rocks only a minute fraction of prehistoric
plants and animals have left any record of their existence. This is not
difficult to understand in view of the rather rigorous requirements of
fossilization.

REQUIREMENTS OF FOSSILIZATION
Although a large number of factors ultimately determine whether an
organism will be fossilized, the three basic requirements are:

1. The organism should possess hard parts. These might be shell, bone,
teeth, or the woody tissue of plants. However, under very favorable
conditions of preservation it is possible for even such fragile material as an
insect or a jellyfish to become fossilized.

2. The organic remains must escape immediate destruction after death. If the
body parts of an organism are crushed, decayed, or badly weathered, this

may result in the alteration or complete destruction of the fossil record of
that particular organism.

3. Rapid burial in a material capable of retarding decomposition. The type
of material burying the remains usually depends upon where the organism
lived. The remains of marine animals are common as fossils because they
fall to the sea floor after death, and here they are covered by soft muds
which will be the shales and limestones of later geologic periods. The finer
sediments are less likely to damage the remains, and certain fine-grained
Jurassic limestones in Germany have faithfully preserved such delicate
specimens as birds, insects, and jellyfishes.

Ash falling from nearby volcanoes has been known to cover entire forests,
and some of these fossil forests have been found with the trees still standing
and in an excellent state of preservation.

Quicksand and tar are also commonly responsible for the rapid burial of
animals. The tar acts as a trap to capture the beasts and as an antiseptic to
retard the decomposition of their hard parts. The Rancho La Brea tar pit at
Los Angeles, California, is famous for the large number of fossil bones that
have been recovered from it. These include such forms as the sabre-tooth
cat, giant ground sloths, and other creatures that are now extinct. The
remains of certain animals that lived during the Ice Ages have been
incorporated into the ice or frozen ground, and some of these frozen remains
are famous for their remarkable degree of preservation.

MISSING PAGES IN THE RECORD
Although untold numbers of organisms have lived on the earth in past ages,
only a minute fraction of these have left any record of their existence. Even
if the basic requirements of fossilization have been fulfilled, there are still
other reasons why some fossils may never be found.

For example, large numbers of fossils have been destroyed by erosion or
their hard parts have been dissolved by underground waters. Others were
entombed in rocks that were later subjected to great physical change, and

fossils enclosed in these rocks are usually so damaged as to be
unrecognizable.

Then, too, many fossiliferous rocks cannot be studied because they are
covered by water or great thicknesses of sediments, and still others are 6
situated in places that are geographically inaccessible. These and many
other problems confront the paleontologist as he attempts to catalog the
plants and animals of the past.

The missing pages in the fossil record become more obvious and more
numerous in the older rocks of the earth’s crust. This is because the more
ancient rocks have had more time to be subjected to physical and chemical
change or to be removed by erosion.

7

DIFFERENT KINDS OF FOSSIL
PRESERVATION

There are many different ways in which plants and animals may become
fossilized. The method of preservation is usually dependent upon (1) the
original composition of the organism, (2) where it lived, and (3) the forces
that affected it after death.

Most paleontologists recognize four major types of preservation, each being
based upon the composition of the remains or the changes which they have
undergone.

ORIGINAL SOFT PARTS OF ORGANISMS
This type of fossil is formed only under very special conditions of
preservation. To be preserved in this manner, the organism must be buried in
a medium capable of retarding decomposition of the soft parts. Materials that
have been known to produce this type of fossilization are frozen soil or ice,
oil-saturated soils, and amber (fossil resin). It is also possible for organic
remains to become so desiccated that a natural mummy is formed. This
usually occurs only in arid or desert regions and when the remains have been
protected from predators and scavengers.

Probably the best-known examples of preserved soft parts of fossil animals
have been discovered in Alaska and Siberia. The frozen tundra of these areas
has yielded the remains of large numbers of frozen mammoths—a type of
extinct elephant (Pl. 49). Many of these huge beasts have been buried for as
long as 25,000 years, and their bodies are exposed as the frozen earth begins

to thaw. Some of these giant carcasses have been so well preserved that their
flesh has been eaten by dogs and their tusks sold by ivory traders. Many
museums display the original hair and skin of these elephants, and some
have parts of the flesh and muscle preserved in alcohol.

Original soft parts have also been recovered from oil-saturated soils in
eastern Poland. These deposits yielded the well-preserved nose-horn, a
foreleg, and part of the skin of an extinct rhinoceros.

The natural mummies of ground sloths have been found in caves and
volcanic craters in New Mexico and Arizona. The extremely dry desert
atmosphere permitted thorough dehydration of the soft parts before decay set
in, and specimens with portions of the original skin, hair, tendons, and claws
have been discovered.

One of the more interesting and unusual types of fossilization is preservation
in amber. This type of preservation was made possible when ancient insects
were trapped in the sticky gum that exuded from certain coniferous trees.
With the passing of time this resin hardened, leaving the insect encased in a
tomb of amber, and some insects and spiders have been so well preserved
that even fine hairs and muscle tissues may be studied under the microscope.

Although the preservation of original soft parts has produced some
interesting and spectacular fossils, this type of fossilization is relatively rare,
and the paleontologist must usually work with remains that have been
preserved in stone.

ORIGINAL HARD PARTS OF ORGANISMS
Almost all plants and animals possess some type of hard parts which are
capable of becoming fossilized. Such hard parts may consist of the shell
material of clams, oysters, or snails, the teeth or bones of vertebrates, the
exoskeletons of crabs, or the woody tissue of plants. These hard parts are
composed of various minerals which are capable of resisting weathering and
chemical action, and fossils of this sort are relatively common.

Many of the fossil mollusks found in the Tertiary and Cretaceous rocks of
Texas have been preserved in this manner. In some of the specimens the
original shell material is so well preserved that the iridescent mother-of-pearl
layer of the shell is found virtually intact. This type of preservation is less
common, however, in the older rocks of the State.

8
PLATE 2
Types of Fossil Preservation

Figures— 9
1. Internal mold of a Texas Cretaceous ammonite (×½).
2. Internal and external molds of gastropods and pelecypods in Cedar Park
limestone member of the Walnut clay of Comanchean age (×½).
Specimen from quarry near Cedar Park, Williamson County, Texas.
3. Internal mold of a Texas Cretaceous pelecypod (×½).
4. Fossil worm tubes on mold of a Cretaceous ammonite (×½).
5. Petrified or permineralized mammal bone of Tertiary age (×½).
6. Internal mold (steinkern) of a typical Texas Cretaceous gastropod (×½).
7. Carbon residue of a Tertiary fish (×¼).

At certain localities in north and central Texas the Woodbine sands of 10
Upper Cretaceous age (geologic time scale and geologic map, Pls. 1,
10) contain large numbers of shark and fish teeth (Pl. 37), fish scales and
vertebrae. The remains of these vertebrates are unusually well preserved and
are prized by both amateur and professional collectors.

Calcareous Remains

Hard parts composed of calcite (calcium carbonate) are very common among
the invertebrates. This is particularly true of the shells of clams, snails, and
corals. Many of these shells have been preserved with little or no evidence of
physical change (Pl. 2).

Phosphatic Remains

The bones and teeth of vertebrates and the exoskeletons of many
invertebrates contain large amounts of calcium phosphate. Because this
compound is particularly weather resistant, many phosphatic remains (such
as the fish teeth in the Woodbine sands) are found in an excellent state of
preservation.

Siliceous Remains

Many organisms having skeletal elements composed of silica (silicon
dioxide) have been preserved with little observable change. The siliceous
hard parts of many microfossils and certain types of sponges have become
fossilized in this manner (Pl. 14).

Chitinous Remains

Some organisms have an exoskeleton (outer body covering) composed of
chitin, a material that is similar to finger nails. The fossilized chitinous
exoskeletons of arthropods and other organisms are commonly preserved as
thin films of carbon because of their chemical composition and method of
burial.

ALTERED HARD PARTS OF ORGANISMS
The original hard parts of an organism normally undergo great change after
burial. These changes take place in many ways, but the type of alteration is
usually determined by the composition of the hard parts and where the
organism lived. Some of the more common processes of alteration are
discussed below.

Carbonization

This process, known also as distillation takes place as organic matter slowly
decays after burial. During the process of decomposition, the organic matter
gradually loses its gases and liquids leaving only a thin film of carbonaceous
material (Pl. 2, fig. 7). This is the same process by which coal is formed, and
large numbers of carbonized plant fossils have been found in many coal
deposits.

In Texas the carbonized remains of plants, fish, and certain invertebrates
have been preserved in this manner, and some of these carbon residues have
accurately recorded even the most minute structures of these organisms.

Petrifaction or Permineralization

Many fossils have been permineralized or petrified—literally turned to
stone. This type of preservation occurs when mineral-bearing ground waters
infiltrate porous bone, shell, or plant material. These underground waters
deposit their mineral content in the empty spaces of the hard parts making
them heavier and more resistant to weathering. Some of the more common

minerals deposited in this manner are calcite, silica, and various compounds
of iron.

Replacement or Mineralization

This type of preservation takes place when the original hard parts of
organisms are removed after being dissolved by underground water. This is
accompanied by almost simultaneous deposition of other substances in the
resulting voids. Some replaced fossils will have the original structure
destroyed by the replacing minerals. Others, as in the case of certain 11
silicified tree trunks, may be preserved in minute detail.

Although more than 50 minerals have been known to replace original
organic structures, the most frequent replacing substances are calcite,
dolomite (a calcium magnesium carbonate), silica, and certain iron
compounds.

Replacement by calcareous material

Calcareous replacement occurs when the hard parts of an organism are
replaced by calcite, dolomite, or aragonite (a mineral which is composed of
calcium carbonate but which is less stable than calcite). The exoskeletons of
many corals, echinoderms, brachiopods, and mollusks have been replaced in
this manner.

Replacement by siliceous material

When the original organic hard parts have been replaced by silica the fossil
is said to have undergone silicification, and this type of replacement often
produces a very high degree of preservation. This is particularly true of the
silicified Permian (geologic time scale, Pl. 1) fossils from the Glass
Mountains in Brewster County. These fossils are embedded in limestone
which must be dissolved in vats of acid, and after the enclosing rock has
been dissolved the residue yields an amazing variety of perfectly preserved
invertebrate fossils (Pl. 3).

Silicified Cretaceous fossils have been recovered from the Edwards
limestone of central Texas. The silicified fauna is restricted to a few

scattered localities, each of which may yield many unusually well-preserved
fossils.

Replacement by iron compounds

Several different iron compounds have been known to replace organic
matter. Many Texas limestones contain fossil snails and clams which have
had their original shell material replaced by iron compounds such as
limonite, hematite, marcasite, or pyrite. Certain of the fossiliferous Tertiary
sandstones of the Texas Gulf Coast area contain large amounts of glauconite
which commonly replaced organic material.

In some areas entire faunas have been replaced by iron compounds. Such is
the case in the famous “Pyrite Fossil Zone” of the Pawpaw formation
(Lower Cretaceous) in Tarrant County. The fossils in this part of the
formation are very small or “dwarfed” and have been replaced by limonite,
hematite, or pyrite. Ammonites, clams, snails, and corals are particularly
abundant at this locality.

TRACES OF ORGANISMS
Fossils consist not only of plant and animal remains but of any evidence of
their existence. In this type of fossilization there is no direct evidence of the
original organism, rather there is some definite indication of the former
presence of some ancient plant or animal. Objects of this sort normally
furnish considerable information as to the identity or characteristics of the
organism responsible for them.

Molds and Casts

Many shells, bones, leaves, and other forms of organic matter are preserved
as molds and casts. If a shell had been pressed down into the ocean bottom
before the sediment had hardened into rock, it may have left the impression
of the exterior of the shell. This impression is known as a mold (Pl. 2). If at
some later time this mold was filled with another material, this produced a
cast. This cast will show the original external characteristics of the shell.
Such objects are called external molds if they show the external features of

the hard parts (Pl. 2, fig. 2) and internal molds (Pl. 2, fig. 3) if the nature of
the inner parts is shown.

Molds and casts are to be found in almost all of the fossil-bearing rocks of
Texas, and they make up a large part of most fossil collections. It is
particularly common to find fossil clams and snails preserved by this
method. This is primarily because their shells are composed of minerals that
are relatively easy to dissolve, and the original shell material is often
destroyed.

12
PLATE 3
Silicified Brachiopods

All specimens from Permian limestones of the Glass Mountains, Brewster
County, Texas

Figures— 13

1, 2. Avonia sp., ×2. Ventral and side view of two pedicle valves showing
long slender spines.
3. Avonia sp., ×6. Young specimen showing attachment ring at apex.
4-6. Muirwoodia multistriatus Meek, ×4. Respectively, side and ventral
view of pedicle valve and dorsal view of brachial valve.
7-9. “Marginifera” opima Girty. Respectively, ventral and side view of
pedicle valve showing long stout spines (×4) and interior of brachial
valve showing muscle scars and brachial ridges (×2).
10-13. Aulosteges tuberculatus R. E. King, ×4. Respectively, side and
interior view of brachial valve showing muscle scars; ventral view of
pedicle valve showing brush of attachment spines on ears; and ventral
view of a young pedicle valve.
14. Avonia sp., ×4. Ventral view of a specimen with long spines.
15, 16. Avonia subhorrida (Meek), ×2. Ventral view of a pedicle valve and
dorsal view of a brachial valve showing spines on both.
17. Avonia signata (Girty), ×2. Dorsal view of a large specimen showing
hairlike spines on brachial valve.
18-20. Prorichthofenia permiana (Shumard). Respectively, side and
posterior view of pedicle valve (×4) and interior of dorsal valve (×2)
showing anchor spines and interior spines of the brachial valve.
21. Heteralosia hystricula (Girty), ×2. Cluster of individuals attached to a
large Marginifera.
Photograph courtesy of Dr. G. A. Cooper, U. S. National Museum.

Tracks, Trails, and Burrows 14

Many animals have left records of their movements over dry land or the sea
bottom. Some of these, such as footprints (Pl. 4), indicate not only the type
of animal that left them but often provide valuable information about the
animal’s environment.

Thus, the study of a series of dinosaur tracks would not only indicate the size
and shape of the foot but also provide some information as to the weight and
length of the animal. In addition, the type of rock containing the track would
help determine the conditions under which the dinosaur lived.

Some of the world’s most famous dinosaur tracks are to be found in the
Lower Cretaceous limestones in Somervell County, Texas. These footprints,
which are about 110,000,000 years old (Pl. 4), were discovered in the bed of
Paluxy Creek near the town of Glen Rose. Large segments of the rock
containing these tracks were collected by paleontologists of the American
Museum of Natural History in New York City and the Texas Memorial
Museum at Austin. Great slabs of limestone were transported to the
museums, replaced in their original position, and are now on display as mute
evidence of the gigantic size of these tremendous reptiles.

Invertebrates also leave tracks and trails of their activities, and these
markings may be seen on the surfaces of many sandstone and limestone
deposits. These may be simple tracks, left as the animal moved over the
surface, or the burrows of crabs or other burrowing animals. Markings of
this sort provide some evidence of the manner of locomotion of these
organisms and of the type of environment that they inhabited.

Coprolites

Coprolites are fossil dung or body waste (fig. 1). These objects can provide
valuable information as to the food habits or anatomical structure of the
animal that made them.

Fig. 1. Sketch of a coprolite—fossilized animal excrement.

Gastroliths

These highly polished well-rounded stones (fig. 2) are believed to have been
used in the stomachs of reptiles for grinding the food into smaller pieces.
Large numbers of these “stomach stones” have been found with the remains
of certain types of dinosaurs.

Fig. 2. Sketch of a gastrolith—the gizzard stone of an ancient reptile.

PSEUDOFOSSILS
Among the many inorganic objects formed by nature there are some that
bear superficial resemblance to plants or animals. Because they are often
mistaken for organic remains, these objects have been called pseudofossils,
or “false fossils.”

Dendrites

Fig. 3. Dendrites. These thin branching mineral deposits bear a marked resemblance to plants,
hence they are called pseudofossils.

Although these closely resemble the remains of ferns or other plant material
(fig. 3), dendrites are actually thin incrustations of manganese dioxide. They
are often found along the bedding planes of Cretaceous and Paleozoic
(geologic time scale, Pl. 1) limestones in many parts of Texas.

15
Plate 4
Dinosaur tracks in limestone in bed of Paluxy Creek near Glen Rose, Somervell
County, Texas.
Photograph courtesy of the American Museum of Natural History.
Permission to reproduce by R. T. Bird.

Slickensides
16

These are striations that are produced when rock surfaces move past each
other while being fractured. Slickensides may superficially resemble certain
of the Pennsylvanian coal plants of Texas.

Since slickensides are commonly at an angle to the bedding plane and plant
remains lie parallel to the bedding plane, the two are usually easily
distinguished.

Concretions

Many shales and sandstones contain hardened masses of minerals and rock
that are often mistaken for fossils. These masses, called concretions, are
usually found weathered out of the surrounding rock and may assume the
shape of bones, flowers, vegetables, turtles, etc. Although these concretions
do not represent organic remains, it is sometimes possible to find true fossils
inside them.

17

WHERE AND HOW TO COLLECT FOSSILS

In fossil collecting, as in most “collecting” hobbies, the key to success lies in
knowing where to look, what equipment to use, and the most effective
methods of collecting.

COLLECTING EQUIPMENT
Fossil collecting is a relatively inexpensive hobby because it requires a
minimum of supplies and equipment. However, as in almost any hobby,
there are certain basic items of equipment that must be acquired.

Hammer

The hammer is the basic tool in the collector’s kit. Almost any type of
hammer is satisfactory, but as collecting experience is gained it may be
desirable to get a geologist’s hammer. These hammers, also called
mineralogist’s or prospector’s picks, are of two types. One type has a square
head on one end and a pick on the other (Pl. 5): the other type is similar to a
stonemason’s or bricklayer’s hammer and has a chisel end instead of the
pointed pick end. The square head of the hammer is useful in breaking or
chipping harder rocks, and the chisel or pick end is good for digging, prying,
and splitting soft rocks.

Collecting Bag

It will be necessary to have some type of bag in which to carry equipment,
fossils, and other supplies. A Boy Scout knapsack, musette bag (Pl. 5),

hunting bag, or similar canvas or leather bag is suitable.

Chisels

A pair of chisels is useful when fossils must be chipped out of the
surrounding rock. Two sizes, preferably ½ and 1 inch, will usually suffice. A
small sharp punch or awl is effective in removing smaller specimens from
the softer rocks.

Wrapping Materials

Some specimens are more fragile than others, and these should be handled
with special care. Several sheets of newspaper should always be kept in the
collecting bag, and each specimen should be wrapped individually as it is
collected. Such precautions taken in the field will usually prevent prized
specimens from being broken or otherwise damaged. In addition to
newspaper, it is wise to carry a supply of tissue paper in which to wrap more
fragile specimens.

Map, Notebook, and Pencil

It is most important to have some method of recording where the fossils
were found. It is very easy to forget where the material was collected, and
one should never rely on memory. A small pocket-sized notebook is
inexpensive and just the right size to carry in the field.

A highway or county map should be used to find the geographic location of
each collecting locality. Maps of Texas counties can be obtained from the
Texas Highway Department, File D-10, Austin 14, Texas. These maps come
in three different sizes, but for most purposes the 18×25-inch sheets, with a
scale of ½ inch = 1 mile, will be satisfactory. These are available for all
counties and may be purchased at a nominal price.

Magnifying Glass

A magnifying glass or hand lens (Pl. 5) is useful for looking at small
specimens and will also prove helpful in examining the finer details of larger

fossils. A 10-power magnification is satisfactory for most purposes, and
several inexpensive models are available.

Paper or Cloth Bags

Small bags are useful in separating specimens from different localities.
Heavy-duty hardware bags for large rough material and medium-weight
grocery bags for smaller specimens may be used. Locality data may be
written directly on the bag or on a label placed inside with the fossils. As an
added precaution some collectors do both. The more serious collector may
want to use a cloth geological sample bag (Pl. 5).

18
Plate 5
FOSSIL COLLECTING EQUIPMENT

GEOLOGIC HAMMER (Chisel end)
MAGNIFYING GLASS
GEOLOGIC HAMMER (Pick end)
COLLECTING BAG
SAMPLE SACK

Other Useful Items
19

The items described above are those that are most needed and constitute the
basic equipment of the fossil hunter. The serious amateur may wish to
include certain additional items which will place his collecting on a more
professional basis. Some of these accessory items are:

1. A topographic map of the collecting area. These are available for many
parts of the State and are published and distributed at nominal cost by the
United States Geological Survey, Washington, D. C., and/or Denver,
Colorado. The Survey can supply an index sheet showing all such maps
available for Texas.

2. A geologic map of the collecting area if one is available. The list of
publications of the Bureau of Economic Geology should be consulted to see
if a geologic report or map of the area has been published. This list may be
obtained without charge from the Bureau of Economic Geology, The
University of Texas, Austin 12, Texas.

3. The geologic map of Texas. Although a geologic map of Texas is included
in this publication (Pl. 10), the scale is so small that its use is somewhat
limited. For more detailed work a larger geologic map in color (scale: 1 inch
= 31.56 miles) may be ordered from the Bureau. The sale price is 25 cents.

4. A compass for more accurate location of collecting localities.

5. Adhesive or masking tape. The locality information can be written on the
tape and applied directly to the specimen.

6. Paper labels (about 3×5 inches). A properly completed label should be
placed inside each bag of material.

WHERE TO LOOK
Knowing where to look for fossils is a very important part of fossil
collecting. It has already been pointed out that igneous and metamorphic
rocks are not likely to be fossiliferous, but that most fossils are found in
marine sedimentary rocks. These sediments were deposited under conditions

that were favorable for organisms during life and which facilitated
preservation after death. Limestones, limy shales, and certain types of
sandstones are typically deposited under such conditions.

One should look particularly for areas where rocks formed from marine
sediments lie relatively flat and have not been greatly disturbed by heat,
pressure, and other physical or chemical changes. If the rocks appear to have
undergone considerable folding and fracturing, there is great likelihood that
any fossils that were present have been destroyed or damaged by this action.

Quarries are good places to look but one should be sure to obtain permission
before entering. Rock exposures in quarries are rather fresh but have
undergone some weathering. Quarries have been opened in many of the
limestone formations of Texas, and large numbers of fine specimens have
been collected in some of these excavations. Certain Lower Cretaceous
limestones are useful for road metal, building stone, or in the manufacture of
portland cement, and extensive quarrying has been undertaken in the
Edwards Plateau region of Texas (Pl. 9). Bones and petrified wood are
frequently found in sand and gravel quarries in many parts of the State.

Particular attention should be given to all railroad and highway cuts as rocks
exposed in this way are usually still in their original position and are fairly
well weathered. Cuts made by recent construction are usually more
productive after they have undergone a period of weathering as this helps to
separate the fossils from their enclosing rocks.

Gullies, canyons, and stream beds are also good places to examine. These
areas are continually subjected to the processes of erosion or stream 20
action, and new material is uncovered year after year.

If there are abandoned coal mines nearby, the dumps of waste rock around
the mine shafts could be checked. A careful examination of such waste may
reveal fine specimens of well-preserved plant fossils.

Coal has been mined in several parts of Texas, and abandoned shafts or
dumps are still present in some counties. The bituminous coals of Texas are
predominantly Pennsylvanian in age, and mining has been carried on in the
following counties: Eastland, Erath, Jack, Palo Pinto, Parker, Wise, Young.

HOW TO COLLECT
When a likely collecting spot has been located, the ground should be
examined very carefully to see if there are any rock fragments which contain
pieces of shell or the imprints of leaves or other organisms.

If the fossils have been freed by weathering, they can be easily picked up
and placed in the bag. Many times, however, it will be necessary to take the
hammer and very carefully remove the surrounding rock. Smaller specimens
may be more safely freed with the careful use of the proper size chisel by
gently tapping the chisel and gradually chipping away the matrix—the rock
that is holding the specimen. After most of the matrix has been removed, the
fossil should be carefully wrapped and placed in the collecting bag.

Before leaving a collecting locality, one should be sure to record its
geographic location and the geologic age of the rock in which the fossils
were found. The place should be located on the map and the locality entered
in the notebook in such a manner that it could easily be located again for
additional collecting. If a county or topographic map is available, it is wise
to mark the locality on the map. The geographic and geologic data should be
written on a label placed in the bag of fossils collected at that particular
locality. In addition, many collectors find it helpful to write the locality on
the outside of each bag of fossils.

Material from separate localities should be kept in individual cloth or paper
bags, and the collector should take every precaution to keep the labels with
their respective fossils. Remember that a fossil without a locality is hardly
worth the paper it is wrapped in.

The collector should always ask the land owner’s permission before entering
or collecting on private property. One should respect all property, especially
livestock and fences, and leave the area cleaner than when entered. If these
precautions are observed, future collectors will probably be welcome to
return for additional collecting.

21

CLEANING AND PREPARATION OF FOSSILS

It is usually necessary to do the final cleaning and preparation of fossils at
home or in the laboratory, for most fossils brought in from the field require
considerable preparation before they are ready for display.

Excess matrix should be carefully removed with hammer and chisel; blows
should always be directed away from the fossil. Smaller tools (needles,
tweezers, and awls) should be used in the final preparation stage, and one
should work carefully to avoid damaging the specimen. Before starting the
final cleaning, it will be helpful to place the fossils in water and let them
soak overnight. This will loosen much of the excess rock, and most of the
softer material can then be removed with a small scrub brush or tooth brush.
Mounted needles can be used to clean more delicate specimens or around the
smaller structures of larger fossils. It may be advisable to use the magnifying
glass when working with small fossils or with delicate surface structures of
larger specimens.

Broken fossils can be repaired with clear plastic household cement, and
specimens that are crumbling may be coated with pure white shellac, thinned
collodion, or clear nail polish. The latter is preferred as it is not as likely to
crack. Fragments of bone are particularly apt to crumble upon exposure to
the air. This type of fossil is normally quite fragile and should be excavated
with great care and shellaced as soon as dry.

Dilute hydrochloric acid may be used in removing silicified fossils from a
calcareous matrix. The material to be etched should be placed in a pottery or
glass container and covered with water. Acid should then be added to the
water very slowly and until large numbers of bubbles are given off. Each

time the bubbling ceases, more acid should be added and this process should
be repeated until the fossil is free of matrix. This procedure should be carried
on in a well-ventilated place, and the acid should be handled with extreme
caution. Hydrochloric acid can cause damage or serious injury and the fumes
are extremely corrosive.

HOW FOSSILS ARE NAMED

In order to get the maximum pleasure out of fossil collecting, most amateur
paleontologists want to identify and classify the fossils that they have
collected. This requires some knowledge of how fossils are classified and
how they receive their scientific names.

THE SCIENCE OF CLASSIFICATION
The number of organisms, both living and extinct, is so great that some
system of classification is needed to link them all together. Many fossils bear
distinct similarities to plants and animals that are living today, and for this
reason paleontological classification is similar to that used to classify
modern organisms. This system, known as the system of binomial
nomenclature, was first used consistently in 1758 by Linné (or Linnaeus), an
early Swedish naturalist.

Scientific names established in accordance with the principles of binomial
nomenclature consist of two parts: the generic (or genus) name and the
trivial name. These names are commonly derived from Greek or Latin words
which are usually descriptive of the organism or fossil being named. They
may, however, be derived from the names of people or places, and in such
instances the names are always Latinized. Greek or Latin is used because
they are “dead” languages and not subject to change. They are also
“international” languages in that scientists all over the world can use the
same names regardless of what language they write in. The system of 22
binomial nomenclature has led to the development of the science of

taxonomy, the systematic classification and naming of plants and animals
according to their relationships.

THE UNITS OF CLASSIFICATION
The world of organic life has been divided into the plant and animal
kingdoms. These kingdoms have been further divided into larger divisions
called phyla (from the Greek word phylon, a race). Each phylum is
composed of organisms with certain characteristics in common. For
example, all animals with a spinal cord (or notochord) are assigned to the
phylum Chordata.

The phylum is reduced to smaller divisions called classes, classes are
divided into orders, orders into families, families into genera, and each
genus is divided into still smaller units called species. A species may be
further reduced to subspecies, varieties, or other subspecific categories, but
these need not concern us in a publication of this nature.

The following table illustrates the use of binomial nomenclature in the
classification of man, a clam, and a dog.

Unit Man Dog Clam
Kingdom Animalia Animalia Animalia
Phylum Chordata Chordata Mollusca
Class Mammalia Mammalia Pelecypoda
Order Primates Carnivora Eulamellibranchia
Family Hominidae Canidae Veneridae
Genus Homo Canis Venus
Species sapiens familiaris mercenaria

The generic name and the trivial name constitute the scientific name of a
species and according to this system of classification the scientific name of
all living men is Homo sapiens. It is obvious that there are many variations
among individual men, but all men have certain general characteristics in
common and are therefore placed in the same species.

In a scientific name, the generic name is always started with a capital letter
and the trivial name with a small letter. Both names must be italicized or
underlined.

The name of the author (the person who first described the fossil) usually
appears following the scientific name. The date of the scientific publication
containing the original description of the fossil is often placed after the
author. For example:
Turrilites worthensis Adkins and Winton 1920

With the large numbers of plants and animals that are living today, plus those
of the past, random naming would result in much confusion. For this reason
scientists have established strict rules that must be followed when a
specimen is named. The strict application of these rules enables scientists in
all parts of the world to assign scientific names without fear of duplication.

23

IDENTIFICATION OF FOSSILS

The beginning collector is usually content to know if his specimen is a clam
or a snail or a fern or a palm leaf. But as the collection grows, it becomes
increasingly desirable to know the scientific name of each fossil.

When he starts to identify fossils it may be helpful to show them to a
geology teacher if a college or university is nearby. Most teachers are glad to
be of help and will probably have similar specimens in their own collections.
As all colleges do not have geology departments, a list of institutions with
geologists on their faculties is included at the end of this section of the
handbook (p. 27). In addition, many of the science teachers in the public
schools are familiar with fossils and can give helpful suggestions as to how
to classify material.

Museums are also good places from which to get help. If the museum has a
geological collection, it will be most helpful to compare specimens with the
fossils in their collections and to ask the museum personnel for advice. In
addition to the above sources of information, local professional geologists
are usually familiar with the geology of the local area and the
paleontological literature of the region.

Possibly local librarians can recommend books, encyclopedias, or other
publications that will be of help. Members of a local rock and mineral club,
if one is available, are another source of information. Many times these
collectors can pass along good ideas and tell exactly which books to consult.

After books or journals describing the fossils of the area have been located,
the collected specimens should be closely compared with any illustrations

that are shown. Each fossil should be examined carefully, its more
characteristic features noted, and it should again be compared with the
illustrations and descriptions in the book. The phylum or class to which the
specimen belongs should be determined first. For example, the genus and
species of a certain fossil may not be known, but it looks like a snail and
accordingly it is named a gastropod (for class Gastropoda, the snail class),
and this is, at least, a start in determining the scientific name of that
particular fossil. The descriptive material in the text of each reference will
usually point out the more detailed features which will be diagnostic of the
genus or species.

The illustrations and descriptive material in this publication will also be of
considerable help in identification. Many illustrations of the more common
invertebrate fossils have been included, but the publication was not designed
primarily for use in fossil identification. Rather, it is intended to guide the
amateur or student who is interested in fossil collecting, and to furnish
suggestions as to how collecting may be more effectively pursued.

USE OF IDENTIFICATION KEYS

Fossil identification keys may be useful in helping the beginning collector
identify specimens. The collector compares a fossil with the key description
and eliminates those characters that do not fit the specimen.

The key used in this handbook is based primarily on symmetry—the orderly
arrangement of the parts of an object with reference to lines, planes, or
points. The shape of the shell or body, presence or absence of coiling, and
presence or absence of body partitions are also useful criteria in identifying
fossils. To use the key the beginner should know something about 24
symmetry. Two major types of symmetry are used in this key.

1. Radial symmetry—the symmetrical repetition of parts around an
axis. This is the symmetry of a wheel, and any vertical section
through the center of the object divides it into symmetrical halves
(fig. 4a).

2. Bilateral symmetry—the symmetrical duplication of parts on each
side of a plane (fig. 5). The plane divides the object into two halves
that are mirror images of each other. This is the symmetry of a plank.

It should be noted that many objects may have both kinds of symmetry. For
example: A cone when viewed from the top has radial symmetry and when
viewed from the side shows bilateral symmetry (fig. 4a, b).

Fig. 4. Types of symmetry in a fossil coral. (a) Radial symmetry. (b) Bilateral symmetry.

Fig. 5. Bilateral symmetry as displayed by a typical fossil brachiopod.

An illustration of the use of the key on pages 26-27 follows. Assuming that a
specimen displays radial symmetry, this means that it belongs under Part I
on the key. If the fossil has a tapering, cylindrical, cone-shaped shell (“A” on
the key), the subheadings under the “A” part of the key are examined.

Should the specimen have a shell which is round, tapering at one end, with
transverse septa or sutures (number 2 under “A”), it is probably a
cephalopod. This is indicated on the right hand side of the page. Number 1
under “A” is eliminated because the fossil did not have longitudinal radial
partitions within the shell.

Some fossils display no apparent symmetry and such a fossil would be
referred to Part III of the key. If this fossil had internal transverse partitions
“A” would be eliminated. If the fossil was not a coiled fossil “B” would also
be eliminated and we would proceed directly to “C”—uncoiled fossils. If the
specimen is a branching twig-like fossil, numbers 1, 2, and 3 would be
eliminated and the specimen referred to number 4 (Branching twig-like
fossils). Should the specimen have evenly distributed relatively large
openings with radial longitudinal partitions or septa, the specimen is
probably a colonial coral (“b” under number 4 on the key). The “a” part of
number 4 would be eliminated because the coral had large openings and
radial longitudinal septa.

Once a tentative identification has been made from the key, pictures 25
and descriptions of this fossil group are examined to establish a more
precise identification. It should be remembered that keys are not perfect, and
the collector should not expect to be able to identify every specimen with
this key.

26

IDENTIFICATION KEY TO MAIN TYPES OF
INVERTEBRATE FOSSILS
(Instructions on pages 23-25 for use of key)

I. Fossils displaying radial symmetry—symmetrical repetition of parts
around a central axis
A. Fossil tapering, cylindrical, cone-shaped:
1. Fossil with longitudinal radial partitions or septa; cone-shaped
Coral
2. Shell with transverse septa or sutures; tapering at one end
Cephalopod

3. Shell without internal septa or partitions:
a. Shell large, heavy; usually with external longitudinal ribs. Occur
only in Cretaceous rocks
Rudistid
b. Shell small (usually less than 2 inches long), tusk-shaped, open at
both ends. Rare in Paleozoic and Mesozoic rocks
Scaphopod
B. Fossil disk-shaped or flattened dome-shaped:
1. Fossil with radiating star pattern on top
Echinoid
2. Fossil subconical to hemispherical, dome-shaped; base concave or
flat; minute pits or pores covering surface; typically small (less
than 3 inches across)
Bryozoa
3. Fossil small (less than ½ inch); generally disk-shaped
Foraminifera (orbitoidid)
4. Fossil disk-shaped or button-like; with longitudinal, radial partitions
or septa
Coral
C. Fossil composed of segments or plates:
1. Fossil composed of circular segments, disks, or chambers; when
united form cylinder:
a. Tapered shell
Cephalopod
b. Non-tapered, segments small and of relatively uniform thickness
with hole in center; individual columnals disk-shaped
Crinoid stem
2. Fossil composed of many-sided plates:
a. Bud-shaped fossil of 13 wedge-shaped plates
Blastoid
b. Cup-shaped fossil of many curved plates surrounded by branching
arms
Crinoid
II. Fossils displaying bilateral symmetry—symmetrical duplication of parts
on each side of a plane
A. Fossil coiled in a single plane:
1. Shell divided by internal transverse partitions or sutures
Cephalopod

2. Shell without internal partitions or sutures
Gastropod
3. Shell small; spindle-shaped; resembles wheat grain. Common in
Pennsylvanian and Permian rocks
Foraminifera (fusulinids)
B. Fossil not coiled:
1. Shells or valves similar to clams:
a. Plane of symmetry parallel to hinge; equivalved
Pelecypod
b. Plane of symmetry (almost bilaterally symmetrical) at right angles
to hinge line; mostly inequivalved; strongly ribbed. “Scallop-
like” with “ears.” Rare in Paleozoic rocks
Pelecypod
c. Plane of symmetry at right angles to hinge line; inequivalved; not
“scallop-like” and without “ears.” Larger valve commonly has
an opening in beak. Common in Paleozoic rocks
Brachiopod
2. Fossil tapering, cylindrical, cone-shaped:
a. Fossil with internal longitudinal, radial septa or partitions; cone-
shaped
Coral
b. Shell with internal transverse partitions or sutures; tapering at one
end
Cephalopod
c. Shell without internal septa or partitions.
(1) Shell large, heavy; usually with external longitudinal ribs.
Occur only in Cretaceous rocks
Rudistid
(2) Shell small (usually less than 2 inches), tusk-shaped, open at
both ends. Rare in Paleozoic and Mesozoic rocks
Scaphopod
3. Fossil heart-shaped, domed or flattened; radial star pattern on top
Echinoid
4. Fossil segmented:
a. Fossil divided into 3 lobes; may be curled up. Not found in
Mesozoic or Cenozoic rocks
Trilobite
b. Fossil flattened or elongate; resembles shrimp, crab, or crayfish

Crustacean
III. Fossils displaying no apparent symmetry
A. Shell without transverse internal partitions or sutures:
1. Shell coiled like ram’s horn, low spired, opening of shell very large;
surface has concentric ridges. Shell has two valves; smaller,
flattened valve not often found. In Texas found only in Cretaceous
rocks
Pelecypod
(Note: Some Paleozoic gastropods, “2,” closely resemble larger valve
of these pelecypods)
27

2. Shell tightly coiled; most have higher spire than “1.” Opening of
shell smaller than “1”; shell not as rough as “1” and has only one
valve
Gastropod
B. Coiled fossils; coiling not in one plane:
1. Shell with transverse internal partitions or sutures:
a. Partitions always smooth; thick shelled; loosely and irregularly
coiled, usually in large compact masses of many individual
shells. Occur only in Cretaceous rocks
Caprinid
b. Partitions (sutures) usually wrinkled; relatively thin shelled;
mostly regularly and tightly coiled; occur as separate individual
specimens
Cephalopod
2. Shell without transverse internal partitions or sutures
Gastropod
3. Solid spiral ridge around central axis; resembles a corkscrew
Bryozoa
C. Uncoiled fossils:
1. Fossil resembles a narrow saw blade; typically found as thin film of
carbon. Not found in Mesozoic or Cenozoic rocks
Graptolite
2. Fossil irregularly cone-shaped; longitudinal radial partitions or septa
Coral
3. Shell resembles a clam or oyster shell but valve or shell not
symmetrical

Pelecypod (mostly oysters)
4. Branching twig-like fossils:
a. Fossils covered with minute pores or openings
Bryozoa
b. Fossils with evenly distributed, relatively large openings with
longitudinal radial partitions or septa
Colonial coral
5. Lace-like fossils; occur as thin sheets or films
Bryozoa
6. Fossils composed of radiating masses of polygonal or circular tubes
containing radial septa
Colonial coral
7. Irregular fossils; typically cylindrical with rough surface:
a. Fossil has large axial opening and thick wall; usually has external
longitudinal ribs. Occurs only in Cretaceous rocks
Rudistid
b. Fossil solid with no large axial opening; surface with small pits or
pores (fewer than in Bryozoa). In Texas, occurs most commonly
in Pennsylvanian and Permian rocks
Sponge

LIST OF TEXAS COLLEGES OFFERING
GEOLOGY COURSES

A.&M. College of Texas, College Station
Amarillo College, Amarillo
Arlington State College, Arlington
Austin College, Sherman
Baylor University, Waco
Blinn College, Brenham
Corpus Christi, University of, Corpus Christi
Del Mar College, Corpus Christi
East Texas State College, Commerce
Hardin-Simmons University, Abilene
Henderson County Junior College, Athens
Houston, University of, Houston
Howard County Junior College, Big Spring
Kilgore College, Kilgore
Lamar State College of Technology, Beaumont
Lee College, Baytown
McMurry College, Abilene
Midwestern University, Wichita Falls
North Texas State College, Denton
Odessa College, Odessa
Pan American College, Edinburg
Rice University, Houston
St. Mary’s University, San Antonio
San Angelo College, San Angelo
San Antonio College, San Antonio

Southern Methodist University, Dallas
South Texas College, Houston
Southwestern University, Georgetown
Stephen F. Austin State College, Nacogdoches
Sul Ross State College, Alpine
Tarleton State College, Stephenville
Texarkana College, Texarkana
Texas Christian University, Fort Worth
Texas College, Tyler
Texas College of Arts and Industries, Kingsville
Texas Technological College, Lubbock
Texas Western College, El Paso
The University of Texas, Austin
Trinity University, San Antonio
Tyler Junior College, Tyler
West Texas State College, Canyon

28
Plate 6
Fossil Identification Chart
I RADIAL SYMMETRY

A. Tapering, cylindrical cone-shaped fossils
1. Cone-shaped with longitudinal partitions or septa
Coral
2. Fossils with septa or sutures; tapering at one end
Cephalopod
3. Shell without internal partitions or sutures
a. Shell large heavy, external longitudinal ribs. Cretaceous only
Rudistid
b. Shell small, tusk-shaped open at both ends. Rare in Paleozoic and
Mesozoic
Scaphopod
B. Disc or dome-shaped fossils
1. Star pattern on top
Echinoid
2. Subconical small pits or pores on top
Bryozoan
3. Small disc-shaped (less than ½ inch)
Orbitoid Foraminifera

4. Disc-shaped or button-like, with longitudinal partitions or septa
Coral
C. Fossils composed of segments or plates
1. Circular discs or chambers; when united form cylinder
a. Tapered shell
Cephalopod
b. Not tapered, segments small of uniform thickness, hole in center
Crinoid Stem
2. Fossil composed of many-sided plates
a. Bud-shaped, 13 wedge-shaped plates
Blastoid
b. Cup-shaped, many curved plates branching arms
Crinoid

29
Plate 7
Fossil Identification Chart
II BILATERAL SYMMETRY

A. Fossil coiled in a single plane
1. Shell divided by internal transverse partitions or sutures
Cephalopod
2. Shell without internal partitions or sutures
Gastropod
3. Shell small, spindle-shaped; resembles wheat grain. Pennsylvanian and
Permian
Foraminifera fusulinid
B. Fossil not coiled
1. Shells or valves similar to clams
a. Plane of symmetry parallel to hinge; equivalved
Pelecypod
b. Plane of symmetry almost at right angles to hinge; strongly ribbed;
“Scallop-like” with “ears”, inequivalved

Pelecypod
c. Plane of symmetry at right angles to hinge-line; without “ears”, not
“Scallop-like”; commonly with opening in beak, inequivalved
Brachiopod
2. Fossil tapering, cylindrical or cone-shaped
a. Cone-shaped, internal longitudinal partitions or septa
Coral
b. Tapered, internal transverse partitions
Cephalopod
c. Shell without internal septa or partitions
(1.) Shell large heavy, longitudinal ribs. Cretaceous only
Rudistid
(2.) Shell small, tusk-shaped, open at both ends, rare in Paleozoic and
Mesozoic rocks
Scaphopod
3. Fossil heart-shaped, domed or flattened; star pattern on top
Echinoid
4. Fossil segmented
a. Divided into 3 lobes, may be curled up. Paleozoic only
Trilobite
b. Flattened or elongate, resembles shrimp
Crustacean
30
Plate 8
Fossil Identification Chart
III NO APPARENT SYMMETRY

A. Shell without transverse partitions or sutures
1. Shell coiled like ram’s horn, low spired; shell has two valves, smaller
flattened valve often missing. In Texas exclusively Cretaceous
Pelecypod
2. Shell tightly coiled, most have higher spire than 1, shell smaller and not
as rough as 1, has only one valve
Gastropod
B. Coiled fossils, coiling not in one plane
1. Shell with transverse internal partitions or sutures
a. Partitions always smooth, thick shelled, loosely and irregularly
coiled, in Texas exclusively Cretaceous
Caprinid
b. Partitions (sutures) generally wrinkled, regularly and tightly coiled
Cephalopod
2. Shell without transverse internal partitions or sutures
Gastropod
3. Solid spiral ridge around central axis, resembles corkscrew
Bryozoan
C. Uncoiled fossils

1. Fossil resembles narrow saw blade. Paleozoic only
Graptolite
2. Fossil irregularly cone-shaped, longitudinal partitions or septa
Coral
3. Shell resembles clam or oyster, nonsymmetrical
Pelecypod (mostly oysters)
4. Branching twig-like fossils
a. Covered with minute pores or openings
Bryozoa
b. With evenly distributed larger openings with septa
Colonial coral
5. Lace-like fossils, occur as thin sheets or films
Bryozoa
6. Masses of circular or polygonal tubes with septa
Colonial coral
7. Irregular fossils, cylindrical with rough surface
a. Large axial opening with thick wall, external longitudinal ribs.
Cretaceous only
Rudistid
b. Solid, no opening, small pits or pores. Pennsylvanian or Permian
Sponge
31

CATALOGING THE COLLECTION

After the fossils have been cleaned and tentatively identified, they should be
cataloged. This is necessary to enable the collector to have a record of his
collection and to furnish as much information as possible about each
individual fossil.

The collecting data can be taken from the labels that were placed in each bag
of fossils as they were collected, or from the field notebook. Actually, it is
wise to check one against the other. This information should then be entered
in some type of record book and also placed on a more permanent label
which is put in the tray or box with the fossil. The catalog and label should
contain such pertinent data as (1) the scientific name of the fossil, (2) the
geologic formation from which the specimen was collected, (3) the exact
geographic location of the collecting locality, (4) the name of the collector,
(5) the date the fossil was collected, and (6) the catalog number of the
specimen. The latter is usually placed in the upper right hand corner of the
label (fig. 6) and corresponds with a like number in the record book.

Specimen No. P-185
NAME Spirifer rockymontanus
FORMATION Big Saline (Penn.)
LOCALITY Little Brady Creek, McCulloch Co.,
Tex.
(1000′ NE of Smith ranch House)
COLLECTOR F. B. Plummer
DATE July 1937

Fig. 6. A brachiopod showing the catalog number on it, and the accompanying label that
pertains to the specimen.

The entries in the catalog should be numbered consecutively, and all
specimens from the same locality should bear the same number. This number
should be written on the fossil with India ink, preferably on any remaining
matrix or on some inconspicuous part of the specimen (fig. 6). If the surface
of the fossil is too coarse or porous for ink, the catalog number can be
written on a small patch of white enamel or clear nail polish painted on the
specimen. After the ink has dried it should be coated with a dab of clear
shellac or clear nail polish to help preserve the number. If each specimen is
numbered, it can easily be identified even if it should become separated from
its label.

HOW FOSSILS ARE USED

Fossils are useful in a number of different ways, for each specimen provides
some information about when it lived, where it lived, and how it lived.

Fossils are very important, for example, in tracing the development of the
plants and animals of our earth. This is possible because the fossils in the
older rocks are usually primitive and relatively simple; but a study of similar
specimens that lived in later geologic time shows that the fossils become
progressively more complex and more advanced in the younger rocks.

Some fossils, for example, the reef-building corals, appear to have always
lived under much the same conditions as they live today. Hence, it is
reasonably certain that the rocks containing fossil reef corals found in 32
place (that is, where they were originally buried), were deposited in
warm, fairly shallow, salt water. By studying the occurrence and distribution
of such marine fossils, it is possible to outline the location and extent of
prehistoric seas. Moreover, the type of fossils present will frequently give
some indication as to the bottom conditions, depth, temperature, and salinity
of these ancient bodies of water.

Probably the most important use of fossils is for purposes of correlation—
the process of demonstrating that certain rock layers are closely related to
each other. By correlating or “matching” the beds containing specific fossils,
it is possible to determine the distribution of geologic units of similar age.
Some fossils have a very limited vertical or geologic range and a wide
horizontal or geographic range. In other words, they lived but a relatively
short period in geologic time but were rather widely distributed during their
relatively short life. Such fossils are known as index fossils or guide fossils

and are especially useful in correlation because they are normally only
associated with rocks of one certain age.

Fig. 7. Sketches of two types of micropaleontological slides. (a) Multiple space faunal slide. (b)
Single-hole slide.

Microfossils are often very valuable as guide fossils for the petroleum
geologist. The micropaleontologist washes the well cuttings from the drill
hole and separates the tiny fossils from the surrounding rocks. The
specimens are then mounted on special slides (fig. 7) and studied under the
microscope. Information derived from these fossils often provides valuable
data on the age of the subsurface formation and the possibilities of oil
production. Microfossils are particularly valuable in the oil fields of the Gulf
Coast region of Texas. In fact, some of the oil-producing zones in this area
have even been named for certain key genera of microfossils. For example,
the “het” zone of Oligocene age (geologic time scale, Pl. 1) is named for the
genus Heterostegina, which is a tiny one-celled animal. Other microfossils,
such as fusulinids, ostracodes, spores, and pollens, are also used to identify
subsurface formations in many other parts of the State.

Plant fossils are very useful as climatic indicators but are not too reliable for
purposes of age determination. They do, however, provide much information

about the development of plants throughout geologic time.

33

GEOLOGIC HISTORY

The geologic history of our earth has been recorded primarily in marine
sedimentary rocks, and this record indicates that our earth is very old and
that life has been present for many millions of years. The earth is not only
extremely old (more than 3½ billion years of age), but it has also undergone
many changes which have taken place slowly but steadily and have greatly
affected both the earth and its inhabitants. The earth’s physical features have
not always been as they are seen today. Geologic research has shown that
mountains now occupy the sites of ancient seas, and that coal is being mined
where swamps existed millions of years ago. Furthermore, there is much
evidence to indicate that plants and animals have also undergone great
change. The trend of this organic change is, in general, toward more
complex and advanced forms of life, but some forms have remained virtually
unchanged and others have become extinct.

In order to interpret geologic history, the earth scientist must attempt to
gather evidence of the great changes in climate, geography, and life that took
place in the geologic past. The record of these changes can be found in the
rocks, and here is found the story of the various events in earth history.

GEOLOGIC COLUMN AND TIME SCALE
In order to discuss fossils and the age of the rocks containing them, it is
necessary to become familiar with the geologic column and the geologic
time scale (Pl. 1).

The geologic column refers to the total succession of rocks, from the oldest
to most recent, that are found either locally or in the entire earth. Thus, the
geologic column of Texas includes all rock divisions known to be present in
this State. By referring to the geologic column previously worked out for
any given area, the geologist can determine what type of rocks he might
expect to find in that particular region.

The geologic time scale is composed of units which represent intervals of
geologic time, during which were deposited the rocks represented in the
geologic column. These time units are used by the geologist to date the
events that have taken place in the geologic past.

The largest unit of geologic time is an era, and each era is divided into
smaller time units called periods. A period of geologic time is divided into
epochs, which, in turn, may be subdivided into still smaller units. The
geologic time scale might be roughly compared to the calendar in which the
year is divided into months, months into weeks, and weeks into days. Unlike
years, however, geologic time units are arbitrary and of unequal duration,
and the geologist cannot be positive about the exact length of time involved
in each unit. The time scale does, however, provide a standard by which he
can discuss the age of fossils and their surrounding rocks. By referring to the
time scale it may be possible, for instance, to state that a certain event
occurred during the Paleozoic era in the same sense that one might say that
something happened during the American Revolution.

There are five eras of geologic time, and each has been given a name that is
descriptive of the degree of life development that characterizes that era.
Hence, Paleozoic means “ancient-life,” and the era was so named because of
the relatively simple and ancient stage of life development.

The eras, a guide to their pronunciation, and the literal translation of each
name is shown below.

Cenozoic (SEE-no-zo-ic)—“recent-life”
Mesozoic (MES-o-zo-ic)—“middle-life”
Paleozoic (PAY-lee-o-zo-ic)—“ancient-life”
Proterozoic (PRO-ter-o-zo-ic)—“primitive-life”
Archeozoic (AR-kee-o-zo-ic)—“beginning-life”

Archeozoic and Proterozoic rocks are commonly grouped together and
referred to as Precambrian in age. The Precambrian rocks have been 34
greatly contorted and metamorphosed, and the record of this portion of
earth history is most difficult to interpret. Precambrian time represents that
portion of geologic time from the beginning of earth history until the
deposition of the earliest fossiliferous Cambrian strata. If the earth is as old
as is believed, Precambrian time may represent as much as 85 percent of all
geologic time.

The oldest era is at the bottom of the list because this part of geologic time
transpired first and was then followed by the successively younger eras
which are placed above it. Therefore, the geologic time scale is always read
from the bottom of the chart upward. This is, of course, the order in which
the various portions of geologic time occurred and during which the
corresponding rocks were formed.

As mentioned above, each of the eras has been divided into periods, and
most of these periods derive their names from the regions in which the rocks
of each were first studied. For example, the Pennsylvanian rocks of North
America were first studied in the State of Pennsylvania.

The Paleozoic era has been divided into seven periods of geologic time.
With the oldest at the bottom of the list, these periods and the source of their
names are:

Permian (PUR-me-un)—from the Province of Perm in Russia
Pennsylvanian (pen-sil-VAIN-yun)—from the State of Pennsylvania
Mississippian (miss-i-SIP-i-un)—from the Upper Mississippi Valley
Devonian (de-VO-ni-un)—from Devonshire, England
Silurian (si-LOO-ri-un)—for the Silures, an ancient tribe of Britain
Ordovician (or-doe-VISH-un)—for the Ordovices, an ancient tribe of Britain
Cambrian (KAM-bri-un)—from the Latin word Cambria, meaning Wales

The Carboniferous period in Europe includes the Mississippian and
Pennsylvanian periods of North America. Although this classification is no
longer used in the United States, the term Carboniferous will be found in
many of the earlier geological publications and on many of the earlier
geologic maps.

The periods of the Mesozoic era and the source of their names are:

Cretaceous (cre-TAY-shus)—from the Latin word creta, meaning chalky
Jurassic (joo-RAS-ik)—from the Jura Mountains of Europe
Triassic (try-ASS-ik)—from the Latin word triad, meaning three

In Texas, the Cretaceous has two divisions, known as either Lower
Cretaceous and Upper Cretaceous or as Comanche series and Gulf series,
respectively. These designations are for rocks of nearly equivalent age, and
both sets of terms have been used by geologists and in publications. In this
handbook, both sets of terms are used interchangeably, that is, Lower
Cretaceous and/or Comanche series and Upper Cretaceous and/or Gulf
series.

The Cenozoic periods derived their names from an old outdated system of
classification which divided all of the earth’s rocks into four groups. The two
divisions listed below are the only names of this system which are still in
use:

Quaternary (kwah-TUR-nuh-ri)
Tertiary (TUR-shi-ri)

While the units discussed above are the major divisions of geologic time, the
geologist usually works with smaller units of rocks called formations. A
geologic formation is identified and established on the basis of definite
physical and chemical characteristics of the rocks. Formations are usually
given geographic names which are combined with the type of rock that
makes up the bulk of the formation. For example, the Beaumont clay was
named from clay deposits that are found in and around Beaumont, Texas.

THE GEOLOGY OF TEXAS
The geologic history of Texas, like the geologic history of the rest of the
earth, is recorded primarily in marine sedimentary rocks. These rocks
provide some knowledge of the early geography and the first inhabitants of
what is now the State of Texas. Most of these rocks were formed from 35

sediments deposited in shallow seas which covered parts of the State at
various times in earth history.

By studying these rocks and their relations to each other, geologists have
established a geologic column for Texas.

Physiography

In order to discuss the distribution and exposures of the rocks of Texas, it is
helpful to be familiar with the physiography of the State. Physiography deals
with the study of the origin and description of land forms, such as
mountains, valleys, and plains. Plate 9 is a map of Texas which shows the
major physiographic provinces within the State.

The majority of the land forms in Texas have been produced by the
processes of erosion attacking the structural features of an area. Certain other
land forms may be related to the effects of igneous activity which resulted in
the accumulation of large masses of igneous rocks. The Davis Mountains are
an example of surface features produced in this manner.

In discussing the physiography of Texas, three major physiographic
provinces will be recognized. These are (1) the Trans-Pecos region, (2) the
Texas Plains, and (3) the Gulf Coastal Plain (Pl. 9).

TRANS-PECOS REGION

The Trans-Pecos region, located in the westernmost part of the State, is an
area of mountains and plateaus with broad basins between the major
mountain ranges. Many different types of rocks are exposed in Trans-Pecos
Texas and these include marine, fresh-water, and terrestrial deposits. In
many areas igneous rocks flowed out on the surface and now overlie
sedimentary rocks. There are also many places where igneous rocks have
been injected into the surrounding rocks, and these igneous rocks have been
exposed by later erosion.

Included within this area is the Van Horn uplift of southern Hudspeth and
Culberson counties, the Solitario uplift of southern Presidio and Brewster
counties, and the Marathon uplift of northeast Brewster County. This region

also includes the Big Bend area of Texas, a part of which has been set aside
as a National Park where many interesting and important geological features
may be seen.

The Trans-Pecos region is one of rugged topography with elevations as high
as 8,700 feet, at Guadalupe Peak in the Guadalupe Mountains of northern
Culberson County, and as low as 1,500 feet, in the Rio Grande valley.

Numerous invertebrate fossils occur in the Cretaceous limestones and shales
of the Trans-Pecos region and in the Paleozoic rocks of the Marathon uplift.
The Gaptank formation of Pennsylvanian age and the Permian reef
limestones of the Glass Mountains are especially fossiliferous. In addition,
many vertebrate fossils have been collected in Trans-Pecos Texas,
particularly in and around Big Bend National Park.

TEXAS PLAINS

The plains of Texas are broad expanses of country with very little surface
relief. Most of the plains support grasses and some have wooded areas,
particularly along stream valleys.

The plains of the northwestern part of the State have been subdivided as
follows.

High Plains

This area (Pl. 9), often called “the caprock,” is an elevated plateau which
rises above the rolling plains which surround it. The High Plains are
bounded by the Pecos River valley on the south, southeast, and west and by
the North-Central Plains on the east.

The surface of the High Plains is very flat and characterized by a sparse
cover of grasses and few trees. The surface strata consist largely of
unconsolidated deposits of sands and gravels of Quaternary and Tertiary age,
with remnants of Lower Cretaceous limestones along the southern margin.
The rocks of the High Plains are mostly unfossiliferous, but mammalian
remains have been found at several localities.

36
Plate 9
Physiographic map of Texas.

HIGH PLAINS
NORTH-CENTRAL PLAINS
GRAND PRAIRIE
TRANS-PECOS TEXAS
VAN HORN UPLIFT
THE BIG BEND AREA

SOLITARIO UPLIFT
MARATHON UPLIFT
EDWARDS PLATEAU
LLANO UPLIFT
BALCONES FAULT ZONE
GULF COASTAL PLAIN

North-Central Plains 37

Surface strata of the North-Central Plains (Pl. 9) are westward-dipping
Pennsylvanian, Permian, and Triassic rocks. Present also are extensive
exposures of Quaternary sands and gravels which trend north-south across
the central portion of the region. The area is bounded on the west by the
High Plains, on the east by the Grand Prairie, and on the south by the
Edwards Plateau and Llano uplift. Many vertebrate fossils have been
collected from the Permian and Triassic rocks of this area. There are also
many excellent outcrops of fossiliferous Pennsylvanian formations in the
North-Central Plains region.

Edwards Plateau

The Edwards Plateau (Pl. 9) is located in south-central Texas and is bounded
on the south by the Balcones fault zone and on the north by the North-
Central Plains. The surface of the area is typically flat with a gentle slope to
the south. The rocks of the Edwards Plateau consist primarily of Lower
Cretaceous limestones and shales, many of which are very fossiliferous.

Grand Prairie

This area (Pl. 9) has a relatively flat surface but there are areas of gently
rolling hills. The eastern boundary of the Grand Prairie is marked partly by
the Balcones fault zone. North of McLennan County, however, the Balcones
fault zone is not expressed at the surface and in this area the eastern
boundary is defined by the western edge of the Woodbine exposures. Upper
and Lower Cretaceous rocks occur at the surface and dip to the southeast;
many of these rocks contain a large number of invertebrate fossils.

Llano Uplift

The Llano uplift (Pl. 9) is located in the central part of the State where
Precambrian igneous and metamorphic rocks and sedimentary rocks of early
Paleozoic age occur on the surface. The area, which now appears as a basin-
shaped depression, was at one time covered by Lower Cretaceous rocks and
perhaps also by Devonian, Mississippian, and Pennsylvanian strata. These
have since been removed by erosion. The east, south, and west sides of the
uplift are surrounded by Lower Cretaceous rocks, and the northern margin is
marked by the Mississippian and Pennsylvanian formations of the North-
Central Plains. The area is, in general, composed of unfossiliferous rocks,
but some invertebrate fossils (primarily trilobites and brachiopods) have
been collected.

GULF COASTAL PLAIN

The Gulf Coastal Plain (Pl. 9) is composed of Cretaceous, Tertiary, and
Quaternary rocks and includes the eastern, southeastern, and southern
portions of the State. The rocks of the area consist of sands, clays, shales,
and limestones. The Texas Gulf Coastal Plain is bounded on the north and
west by the Balcones fault zone, on the south and southwest by the Gulf of
Mexico, and extends eastward into Arkansas and Louisiana.

The region has broad river valleys and uplands of low relief, but there is an
increase in relief toward the interior of the State. The surface of the area
slopes gradually toward the Gulf and successively younger formations are
encountered gulfward.

The rocks of the Texas Gulf Coastal Plain are relatively unfossiliferous, but
many of the Upper Cretaceous rocks contain fossils. In the central portion of
the region some marine formations of Tertiary age locally contain well-
preserved invertebrate fossils.

Geology
Geologic studies of the State of Texas have indicated the presence of rocks
formed during every era and period of geologic time. These range from the
Precambrian granites of the Llano uplift to the Quaternary gravels of the
High Plains.

38

Plate 10
GENERALIZED GEOLOGIC MAP OF TEXAS
Modified from Geologic Map of Texas, 1933

This map in a higher resolution

One of the best ways to become acquainted with the geology of Texas 40
is to study the geologic map of the State (Pl. 10). A geologic map
shows the distribution and age of surface rocks and may also indicate what
kind of geologic structures are present. The types of rocks that crop out at

the surface may be shown by means of symbols, colors, or patterns, and
these are explained by a legend which accompanies the map. On Plate 10,
colors are used to show the distribution and geologic age of the surface rocks
of Texas. Reference to this map will give the collector some idea of the age
of the fossils that might be found in a given area. Some special geologic
maps may have the location of geologic structures and formation contacts
indicated by means of symbols, such as dashed lines, arrows, and similar
special markings. However, the map included in this publication does not
show any of these special markings.

PRECAMBRIAN ROCKS

The Precambrian rocks of Texas are composed of igneous and metamorphic
rocks and some sedimentary rocks. Most of the Precambrian outcrops are in
the Llano uplift and El Paso and Van Horn regions.

Alterations produced by vast amounts of time, heat, and pressure have
obliterated any trace of fossils that may have been present in these rocks.
With the exception of some questionable primitive plants collected in the
Van Horn region, no Precambrian fossils have been reported from Texas.

PALEOZOIC ROCKS

Rocks of Paleozoic age are widespread in Texas, and rocks of each period
are well exposed. Outcrops are found in the Llano uplift, North-Central
Plains, and Trans-Pecos region. The most extensive exposures are of
Pennsylvanian and Permian age, and the former are highly fossiliferous in
parts of the North-Central Plains.

Cambrian

Rocks of late Cambrian age are exposed in the Llano, Marathon, and
Solitario uplifts, and the Franklin Mountains near El Paso. These are
sedimentary rocks consisting of conglomerates, sandstones, shales,
limestones, and some dolomites.

Some of these formations are relatively fossiliferous, but the specimens are
commonly fragmental and very poorly preserved. Fossils that are apt to be

found in the Cambrian rocks of the Llano uplift include brachiopods,
gastropods, trilobites, and small rounded objects believed to have been
formed by algae (primitive one-celled plants). In other parts of the State,
Cambrian rocks are sparsely fossiliferous and the fossils consist primarily of
fragmental brachiopods, trilobites, and algae.

Ordovician

Ordovician outcrops are present in the Llano uplift of central Texas and in
the Marathon, Solitario, El Paso, and Van Horn regions of Trans-Pecos
Texas. These are sedimentary rocks and consist largely of sandstones, cherts,
limestones, and dolomites.

Although some of the Ordovician formations are fossiliferous, they are
seldom collected by amateur paleontologists because they are exposed in
relatively inaccessible places and the fossils are usually poorly preserved.
Ordovician fossils reported from Texas include sponges, corals, brachiopods,
gastropods, cephalopods, and trilobites. In addition, the Marathon formation
of the Marathon uplift contains large numbers of well-preserved graptolites
(fig. 24, p. 86).

Silurian

The Silurian of Texas is poorly represented in surface exposures, and only
one formation, the Fusselman, has been described. The Fusselman crops out
in the El Paso and Van Horn regions where it is a white dolomitic limestone.
Fossils are not abundant in this formation, but brachiopods and corals have
been collected at a few localities.

Devonian

Devonian rocks are best developed in Trans-Pecos Texas, especially in the
Marathon, El Paso, and Van Horn regions. In addition to the Trans- 41
Pecos exposures, there are minor outcrops of Devonian rocks in the
Llano uplift of central Texas.

Fossils are rare and fragmental in the Trans-Pecos exposures and consist
primarily of radiolarians and brachiopods. The Devonian rocks of central
Texas are predominantly calcareous and, although the material is usually

poorly preserved, many fossils have been collected from them. These
include bryozoans, corals, brachiopods, gastropods, and trilobites.
Conodonts and fragments of primitive armored fishes (Pl. 37) have also been
reported.

Mississippian

Mississippian rocks are exposed in the Llano region and in the Hueco
Mountains of the Trans-Pecos area. The Trans-Pecos rocks primarily contain
brachiopods with some bryozoans and gastropods.

The central Texas Mississippian rocks are much more fossiliferous and some
of the material is well preserved. Fossils reported from this area include
brachiopods (Pl. 17), crinoids, gastropods, cephalopods, trilobites, and
ostracodes.

Pennsylvanian

Pennsylvanian rocks are well represented in Texas and are exposed in the
Llano uplift, north-central Texas, and Trans-Pecos Texas.

In Trans-Pecos Texas fossiliferous rocks crop out in the Hueco and Diablo
Mountains. Fossils found in this area are algae, fusulinids, corals,
brachiopods, pelecypods, gastropods, cephalopods, and crinoids. There is
also a thick section of Pennsylvanian rocks in the Marathon uplift, but only
one formation, the Gaptank, is very fossiliferous. It contains many fossils
including fusulinids, sponges, corals, bryozoans, brachiopods, gastropods,
pelecypods, cephalopods, and crinoids.

Certain Pennsylvanian strata in the Llano region are very fossiliferous, and
the material is well preserved. The more abundant forms are fusulinids,
corals, brachiopods, gastropods, pelecypods, cephalopods, and crinoids.

Probably the best Pennsylvanian collecting areas are to be found in north-
central Texas. Here the thick marine limestones and shales contain large
numbers of well-preserved invertebrate fossils, and the terrestrial or shallow
marine strata have yielded an abundance of plant fossils. Invertebrate fossils
are apt to be found along the banks of streams and gullies and in railroad and
highway cuts. Many of the limestones bear large numbers of fusulinids or

crinoid stems, and the shales may contain many corals, brachiopods, and
mollusks. The best collecting will, of course, be found where the rocks have
been sufficiently weathered.

Fig. 8. Sketch of typical crinoidal limestone from the Pennsylvanian of north Texas.

Typical invertebrate fossils are foraminifera (principally fusulinids), corals
(especially the solitary or “horn” corals), brachiopods, bryozoans (the lacy
and branching types are most common), pelecypods, gastropods (exhibiting
a variety of coiling), cephalopods (nautiloids and goniatites predominate),
and crinoids, which in many areas are found in thick crinoidal limestones
(fig. 8). Some typical Pennsylvanian fossils are illustrated in Plates 14, 15,
17, 18, 19, 20, 21, 24, 32, and 35.

Permian

Permian rocks are found in widely separated areas in Texas. The best
exposed section of marine Permian rocks is found in the Glass Mountains of
Brewester County, and many of these rocks are very fossiliferous. The 42
original shell material of some of the Permian fossils of this area has

been replaced by siliceous material which is very well preserved. These
silicified fossils are removed from the limestone by solution in acid, and
some most remarkable specimens have been recovered in this manner (Pl.
3). Brachiopods are the most common fossils, but corals, bryozoans, and
mollusks have also been recovered.

Extensive Permian exposures occur also in the central part of the North-
Central Plains region. These rocks were formed from sediments of both
marine and continental origin and some of them are fossiliferous. The
marine rocks contain a variety of invertebrate fossils including brachiopods,
pelecypods, gastropods, and ammonoids. Those rocks representing terrestrial
deposits contain vertebrate remains at many localities, and numerous
amphibians and primitive reptiles (Pl. 40) have been collected from them.

MESOZOIC ROCKS

Mesozoic rocks occur over a wide area of Texas and include exposures of
Triassic, Jurassic, and Cretaceous age. Many of the Upper and Lower
Cretaceous outcrops are quite fossiliferous and easily accessible and thus of
considerable interest to many amateur collectors.

Triassic

Triassic rocks crop out in parts of the High Plains, the Glass Mountains of
Trans-Pecos Texas, and parts of Pecos, Crockett, Upton, Reagan, and
Glasscock and other west Texas counties. These are predominantly
nonmarine rocks consisting of conglomerates, sandstones, shales, and some
gypsum beds.

Triassic fossils are almost exclusively vertebrates, although some poorly
preserved plant and invertebrate remains have been reported. Fossil
vertebrates of the Texas Triassic include phytosaurs (Pl. 42), crocodiles,
amphibians, and fish.

Jurassic

In Texas, surface exposures of Jurassic rocks are known only from Malone
Mountain in southwestern Hudspeth County. The rocks there are limestones,

shales, sandstones, and conglomerates. Fossils reported from that locality
include marine and fresh-water pelecypods, fresh-water gastropods, and
ammonites.

Cretaceous

Rocks of Cretaceous age are widely distributed in Texas and represent one of
the more important rock systems of the State. Cretaceous outcrops occur in
central Texas, north Texas, the Edwards Plateau, parts of the High Plains, the
Gulf Coastal Plain, and Trans-Pecos Texas.

As mentioned earlier, the Texas Cretaceous has been divided into the Lower
Cretaceous (Comanche series) and Upper Cretaceous (Gulf series). These
rocks consist primarily of marls (a type of calcareous clay), shales, chalks,
and limestones, but sands and conglomerates also occur. Cretaceous rocks
occur on the surface of about 28 percent of Texas, and many of the larger
cities of the State are situated on Cretaceous strata.

Many of the Gulf and Comanche formations contain fossils which are of
interest both to amateur and professional paleontologists. Because of their
wide distribution in and near large population centers, Cretaceous outcrops
can be conveniently visited by many amateur fossil collectors. The fossils
are usually abundant and varied, and some are well preserved. Although
numerous kinds of fossils may be collected, the more common forms are
cephalopods, pelecypods, gastropods, and echinoids. Some of the more
typical Cretaceous fossils are shown in Plates 16, 21, 25-28, 32, 33, 35, and
36.

Cretaceous fossils are more commonly found in shales and chalky
limestones. Fossiliferous outcrops of these rocks can be found along many
streams, roads, and highways of central Texas, north Texas, and the Edwards
Plateau. Outcrops which have been weathered are more likely to provide
good collecting. In general, collecting is poor in areas covered with heavy
vegetation or recent stream deposits. Good collecting localities are 43
outcrops which have a fairly steep slope with a covering of weathered
rock material and a minimum of vegetation. One should move slowly from
the base of the slope upward while searching the ground for any evidence of
fossils, and particular attention should be given to any small gullies since

these often contain fossils that have been washed out of upper beds in the
exposure.

CENOZOIC ROCKS

Cenozoic rocks are widespread in Texas but occur primarily in a broad belt
along the Gulf Coastal Plain. In addition, there are exposures of nonmarine
Cenozoic strata in the High Plains, North-Central Plains, and Trans-Pecos
region. There are also many exposures of Cenozoic igneous rocks in Trans-
Pecos Texas.

Rocks of Cenozoic age occur in more than one-third of Texas and consist of
conglomerates, sands, clays, and some limestone and lignite beds.

Tertiary

Extensive exposures of Tertiary rocks trend northeast-southwest in a broad
band across the Gulf Coastal Plain area. These strata, consisting of sands,
clays, and poorly consolidated limestones, are underlain by Cretaceous
rocks.

Invertebrate fossils are common in certain Tertiary formations and
pelecypods, gastropods, and corals are the predominant forms. In general,
however, fossiliferous exposures are of local occurrence and most of the
Tertiary formations are unfossiliferous. Those Tertiary invertebrates that are
present, however, are often well preserved and represent many interesting
types (Pls. 16, 22, 23, 29, 30, 31).

Tertiary invertebrate fossils are commonly found in sands, clays, and marls.
Many of these sands and marls have a green color which is due to the
presence of glauconite (a green mineral containing iron and closely related
to the micas). At certain localities on the Gulf Coastal Plain the glauconite
marls and sands of the Weches and Crockett formations contain large
numbers of well-preserved clams, snails, and corals. Fossiliferous exposures
of Tertiary rocks are sometimes found in road cuts, but better exposures may
be found along the banks of rivers and creeks. Certain bluffs along the
Brazos, Sabine, and Trinity rivers are well-known Tertiary fossil collecting
localities. Many of these better localities are listed in some of the Bureau of

Economic Geology bulletins included in the bibliography of this publication
(pp. 109-110).

Quaternary

Quaternary deposits of Pleistocene age (geologic time scale, Pl. 1) are found
in many parts of Texas and consist of sands, clays, and gravels.

These rocks are distributed along the Gulf Coast in a belt from 50 to 100
miles wide. They occur also as stream terraces in the Edwards Plateau and
North-Central Plains regions. In addition, Quaternary sands and gravels are
widely distributed over the surface of much of Trans-Pecos Texas. There are
also fossiliferous Pleistocene strata in the High Plains region.

Invertebrate fossils are rare in Pleistocene rocks, but some fresh-water and
terrestrial mollusks occur. Vertebrate remains, however, are abundant in
many localities, and large numbers of horses, camels, mammoths, and other
mammals (Pls. 46-49) have been collected. Fossil bones and teeth (figs. 25,
26, p. 104) are commonly found in the gravels and sands of many of the
river terraces of the State.

44

MAIN TYPES OF FOSSILS

The beginning fossil collector is usually amazed by the many different plants
and animals that have left some trace of their existence. In order to
understand these different types of prehistoric life, it is necessary to know
something about the organisms that are living today.

This handbook discusses the more important groups of plants and animals
which have left some sort of paleontological record, and each major group
begins with a discussion of the more simple organisms and continues
through the more advanced forms. Because scientific workers do not always
agree on exactly the same classification, the system adopted in this
handbook contains the latest ideas of several workers. It is simple enough to
understand, yet complete enough to help one know and classify his fossils. It
should be noted that this classification may differ in some respects from that
of certain older paleontological publications. Therefore, it has seemed
advisable to list other names for some of the groups that are discussed.

In some instances, the brief descriptions and illustrations of each group will
enable the collector to make a preliminary identification of his fossils. For
more detailed information about each group, the reader should refer to
“Books About Fossils” (pp. 108-110).

This part of the handbook begins with a brief summary of the major groups
of the plant kingdom, followed by a discussion of the characteristics and
relative paleontological importance of the various invertebrate animals.
Emphasis is placed on the invertebrates because this type of fossil is most
commonly collected by the amateur. Finally, there is a general review of the
vertebrates.

PLANT FOSSILS
Plant fossils are usually fragmental and poorly preserved, and this tends to
discourage most amateurs from an active interest in paleobotany. However,
in spite of these problems, much is known of the evolution of plants, and
plant fossils provide much information about life of the past. In addition,
certain plants are of considerable value as indicators of ancient climatic
conditions, and their remains have played a large part in the formation of
vast coal deposits.

Classification of the Plant Kingdom

In the following classification only the larger taxonomic groups are
discussed. Notice that the term division has been used in place of the term
phylum as used in the animal kingdom. This usage is now preferred by many
botanists and paleobotanists.
DIVISION THALLOPHYTA

Thallophytes are simple plants without roots, stems, or leaves. They include
the fungi, algae, and diatoms (Pl. 12). Diatoms are microscopic fossils that
are found in many of the rocks of Texas, and they are quite abundant in
Recent sediments as well. Certain of the Paleozoic limestones of central
Texas contain banded spherical masses of algae called “algal biscuits.”
Although not particularly useful fossils, thallophytes have a long geologic
history and are known in rocks ranging from Precambrian to Recent in age.
DIVISION BRYOPHYTA

The bryophytes are simple rootless plants and include the mosses and
liverworts. Although more complex, the bryophytes resemble the algae in
some respects. They are uncommon fossils, but undoubted bryophytes
(liverworts) have been reported from rocks as old as Mississippian.
DIVISION TRACHEOPHYTA

This division has been divided into four subdivisions, among which are
many of the more common living and fossil plants. Such important plants as
the ferns, evergreens, hardwood trees, and the flowering plants are all

tracheophytes. Among the more common and abundant fossil tracheophytes
are the ferns, cycads, and Gingko, in addition to such important “coal plants”
as the scale trees, club mosses, and scouring rushes (Pls. 12, 13). The latter
commonly occur in many of the world’s great coal deposits, and their
remains make up a large part of the coal. Plant fossils of this type may be
collected in the dumps around some of the abandoned coal mines in north-
central Texas and from other Pennsylvanian rocks in north and Trans-Pecos
Texas.

45
Plate 11
GEOLOGIC RANGE OF THE MAJOR GROUPS OF PLANTS AND ANIMALS
The bands give some indication of the geologic range and relative abundance of the
major groups of plants and animals. An increase in the width of the range band
corresponds to a relative increase in numbers during the corresponding portion of
geologic time.

PRECAMBRIAN
PALEOZOIC
CAMBRIAN
ORDOVICIAN
SILURIAN
DEVONIAN
MISSISSIPPIAN
PENNSYLVANIAN
PERMIAN
MESOZOIC
JURASSIC
CRETACEOUS
CENOZOIC

Thallophyta
Bryophyta
Tracheophyta
Protozoa
Porifera
Coelenterata
Bryozoa
Brachiopada
Mollusca
Annelida
Arthropoda
Echinodermata
Chordata

46
Plate 12
FOSSIL PLANTS

THALLOPHYTES

DIATOMS × 900
ALGAE × 400

TRACHEOPHYTES

LEPIDODENDRON × ½
SIGILLARIA × ½

47
Plate 13
FOSSIL PLANTS
TRACHEOPHYTES

NEUROPTERIS × ½
PSILOPHYTON × ⅓
CALAMITES × ½
AMELANCHIER × ½
CORDAITES × ¼
GINGKO × ½

Fairly well-preserved plant remains may also be collected from the 48
Woodbine group of the Upper Cretaceous in north Texas, and fossil
wood, most of it silicified, has been reported from rocks of almost all ages
and in almost every section of the State. In addition, some of the
carbonaceous clays and shales of east Texas contain large assemblages of
plant leaves, which in some places are well preserved.

It is also possible to find the fossilized remains of seeds, spores, and pollen.
Because of their small size, these minute remains are not destroyed by the
drill bit and can be brought out of deep wells without being damaged, and
for this reason they are a valuable tool for the micropaleontologist.

ANIMAL FOSSILS
The fossilized remains of animals are very common in many of the
sedimentary rocks of Texas. These remains are of many different kinds and
represent the fossils of such diverse organisms as the shell of a tiny one-
celled animal or the bones or tusk of a huge elephant. The fossils most
commonly found, however, are the remains of invertebrate animals such as
clams, snails, and corals, and it is this type of fossil that attracts the interest
of most amateur collectors.

It is not always easy to tell whether certain organisms are plants or animals,
and because of this some scientists have suggested that these “in-betweens”
be placed in a separate kingdom—the Protista. The protistans are primarily
unicellular organisms and are represented by such forms as bacteria, algae,
diatoms, and the protozoans (see below). But in this publication, only the
plant and animal kingdoms are recognized.

Phylum Protozoa

This phylum is composed of simple one-celled animals many of which have
no shell or external body covering. Some, however, have external hard parts
that can become fossilized, and these forms are quite useful microfossils.

CLASS SARCODINA.—
This class contains a group of one-celled animals which may secrete an
exoskeleton (external protective covering) of chitin, silica, or calcium
carbonate. Included in this class are foraminiferans (commonly called
forams) and radiolarians.

Order Foraminifera.—
Members of this order secrete tiny chambered shells which are very useful
microfossils. The forams are predominantly marine organisms and have
shells composed of chitin, silica, or calcium carbonate. In addition, some
forms construct a shell of sand grains or some other material which is
cemented together by a sticky substance that is secreted by the animal.

Forams are very abundant in the rocks of Texas and particularly so in rocks
of Mesozoic and Cenozoic age. The most numerous and easily observed
Paleozoic foraminiferans are the fusulinids (fig. 9a), and their small spindle-
shaped remains are very abundant in many of the Pennsylvanian limestones
of north-central and Trans-Pecos Texas. Some typical Texas forams are
illustrated in figure 9.

Order Radiolaria.—
The radiolarians (fig. 10) have delicate spine-covered shells composed of
silica, and their remains are very abundant in certain recent marine
sediments. They may also be found as fossils and have been reported from
Devonian and Permian rocks in Trans-Pecos Texas, and probable 49
radiolarians have been reported from still younger beds.

Fig. 9. Typical Texas Foraminifera (all greatly enlarged). (a) Fusulina (Pennsylvanian). (b)
Robulus. (c) Globigerina. (d) Frondicularia. (b-d, Cretaceous).

Fig. 10. Typical radiolarians (greatly enlarged). (a) Actinomma (Recent). (b) Porodiscus
(Eocene).

Phylum Porifera

These are sponges and are the simplest of the many-celled animals. Living
sponges secrete a skeleton which may be composed of chitin, silica, or
calcium carbonate. These substances are commonly found in the form of
spicules—tiny hard parts that are used to help support the soft tissues of the
animal. These spicules take on a variety of shapes (Pl. 14) and are
occasionally found as microfossils in some marine sediments.

Although sponges are not particularly common fossils, their remains occur
in some parts of the State. Sponges have been collected from Paleozoic and
Mesozoic formations of north and Trans-Pecos Texas, and their spicules
have been reported from well cuttings.

Phylum Coelenterata

The coelenterates are multicelled animals which, though more complex than
the sponges, are rather primitive animals. The living animal is characterized
by a sac-like body cavity, a definite mouth, and tentacles which bear stinging
cells. Some forms, for example, the jellyfishes, have an umbrella-shaped
body and are single free-moving organisms. Others, like the colonial corals,
are composed of many individuals living together in a colony.

Most zoologists and paleontologists recognize three classes of coelenterates:
(1) the Hydrozoa, containing the small animals known as hydroids, (2) the
Scyphozoa, which includes the jellyfish, and (3) the Anthozoa, which
includes the corals and sea anemones. Because of their extreme fragility and
lack of hard parts, hydrozoans and scyphozoans are not commonly found as
fossils. They do, however, have a long geologic history and may be
preserved when unusual conditions of fossilization occur. The anthozoans,
especially the corals, are by far the most important class geologically, and
these forms have left a very good paleontological record.

CLASS ANTHOZOA.—
This class is composed of a group of exclusively marine organisms and
includes the corals and sea anemones. The coral animal, or polyp, secretes a

cup-shaped calcareous (limy) exoskeleton. This skeleton, called a corallite,
is usually divided by radial partitions called septa. The polyp lives in the
calyx, which is the central bowl-shaped depression in the top of the corallite
(fig. 11a).

Solitary corals form an individual corallite for each polyp, and because of
their shape these may be given such names as “horn corals”
(Lophophyllidium, Pl. 15) or “button corals” (Micrabacia, Pl. 16). Colonial
or compound corals (Pl. 15) live together in colonies, which are formed of
many individual skeletons attached to each other (fig. 11b), and the
compound mass of coral skeletons formed in this manner is called a 50
corallum. Fossil corals commonly occur in many marine limestones
and in places constitute a large portion of the rock.

Fig. 11. Morphology and principal parts of corals. (a) Solitary or “horn” coral. (b) Colonial or
compound coral.

a
Columella
Septum
Corallite
b
Calyx
Septum
Corallum

The class Anthozoa has been divided into several subclasses, but only one,
the Zoantharia, is of paleontological importance.

Subclass Zoantharia.—
Most corals and all sea anemones belong to this subclass. Zoantharians are
either colonial or solitary and, because most of them possess a hard
preservable exoskeleton, they are the most important group of anthozoans
geologically. The various orders of the subclass Zoantharia are discussed
below.

Order Rugosa.—
These are corals in which the septa are arranged in cycles of four. Both
solitary and colonial forms occur, and they are found only in rocks of
Paleozoic age. Rugose corals are abundant in many of the Paleozoic
formations of Texas, and two of the more typical forms (Lophophyllidium
and Caninia) are illustrated in Plate 15. Members of this order have been
placed in the subclass Tetracoralla of older classifications.

Order Scleractinia.—
The scleractinians are solitary or colonial corals in which the septa grow in
multiples of six, and they are the most important and abundant of the modern
corals. These corals were the dominant reef builders of Mesozoic and
Cenozoic seas, and their remains are common in many of the marine
formations of the State. Plate 16 illustrates some typical scleractinian corals
from the rocks of Texas. This order has also been referred to as subclass
Hexacoralla, and its members have been called hexacorals.

Order Tabulata.—
These are corals that are now extinct but are known from fossils in both
Paleozoic and Mesozoic rocks. Tabulate corals are characterized by
horizontal partitions called tabulae, and septa are absent or poorly
developed. The tabulates were the most abundant reef-building corals during
Paleozoic time and are well known as fossils. Because of certain similarities
with other anthozoans, some paleontologists have treated the Tabulata as a
distinct subclass rather than as an order of the Zoantharia.

Tabulate corals are not uncommon in many of the Paleozoic rocks of Texas,
and two of these (Cladochonus and Striatopora) are illustrated in Plate 15.

Phylum Bryozoa

Fig. 12. Two types of bryozoans or “moss animals.” (a) Section of the lacy type bryozoan. (b)
The spiral axis of Archimedes (Mississippian).

Bryozoans are colonial animals that are often referred to as “sea mats.” They
have been called this because they are commonly found matted on shells,
rocks, fossils, and other objects. The living animal is quite small, has a
tentacle-bearing ridge surrounding the mouth, and secretes a tiny cup-like
exoskeleton composed of calcareous or chitinous material. These little
chambers, known as zooecia (or autopores), are seen as small pits on the
surface of the bryozoan colony (Rhombopora, Pl. 17). The zooecia grow
together to form the bryozoan colony, and some fossil colonies grow to be as
much as 2 feet across. Such colonies may be spiral (fig. 12b), branching, or
lace-like (fig. 12a), and the latter two types are very common in many of the
fossiliferous strata of Texas. Undoubted bryozoan fossils have been recorded
in rocks of Lower Ordovician age, but questionable Cambrian forms have
also been reported. Bryozoans are abundant in the seas of today, but only a
few forms inhabit fresh waters.

51
Plate 14

SPONGE SPICULES
(GREATLY ENLARGED)

PALEOZOIC SPONGES

MEANDROSTIA × 1
HELIOSPONGIA × 1
ASTRAEOSPONGIUM × ½
ASTYLOSPONGIA × ½
RECEPTACULITES × ½
GIRTYOCOELIA × 2

52
Plate 15
PENNSYLVANIAN CORALS

CLADOCHONUS × 1

STRIATOPORA × 1
LOPHOPHYLLIDIUM PROLIFERUM × 1
MICHELINIA × 1
CANINIA × 1
LOPHOPHYLLIDIUM RADICOSUM × 1

53
Plate 16

CRETACEOUS CORALS

CLADOPHYLLIA × 1
PARASMILIA × 1
PLEUROCORA × 1

TERTIARY CORALS

ENDOPACHYS × 1
ASTRHELIA × 1
FLABELLUM × 1
MICRABACIA × 2
TROCHOSMILIA × 1

In Texas one may expect to find bryozoan remains in the 54
Pennsylvanian rocks of north-central and Trans-Pecos Texas where
they are abundant in certain of the marine shales and limestones. Bryozoans

may also be collected from some Cretaceous and Tertiary beds, but their
remains are small and fragmental and they are easily overlooked. Bryozoans
have also been found matted on the shells of fossil mollusks and other
invertebrates.

Phylum Brachiopoda

The brachiopods are a large group of exclusively marine organisms with
shells composed of two pieces called valves (fig. 13). These valves are
usually composed of calcareous or phosphatic material and enclose and
protect the soft parts of the brachiopod animal. The soft parts are composed
of muscles, the mantle (which secretes the valves), digestive, respiration,
reproductive, and excretory organs, and the tentacle-bearing lophophore.

In adult life the brachiopod is attached to the sea bottom by means of a
fleshy stalk called the pedicle (fig. 14), and this is usually extruded through a
hole (the pedicle foramen) which is located in the ventral or pedicle valve.
The upturned area which is usually present on the pedicle valve is called the
beak. The other valve, known as the dorsal or brachial valve, is usually the
smaller of the two (fig. 13b). The two valves are opened by means of
muscles, and since death results in relaxation of these muscles, fossil
brachiopods are typically found with valves closed.

Brachiopods vary greatly in size and shape and exhibit a wide variety of
ornamentation, such as spines, ribs, nodes, and other structures. They are
abundant fossils in many of the Paleozoic rocks of Texas but are relatively
rare in Mesozoic and Cenozoic formations.

The phylum has been divided into two subclasses, the Inarticulata and the
Articulata. This classification is based upon the nature of the hinge-line—the
edge of the shell where the two valves articulate.

Fig. 13. Morphology and principal parts of articulate brachiopods.

a
Pedicle foramen
Hinge line
b
Pedicle valve
Beak
Brachial valve

CLASS INARTICULATA.—
The members of this class are rather primitive and have a long geologic
history. These brachiopods have valves which are not provided with hinge
teeth, the valves being held together by muscles, and a hinge-line is lacking
(fig. 14). Most inarticulate brachiopods are circular or tongue-like in shape
and commonly composed of chitinous and phosphatic material. Inarticulate
brachiopods range from Lower Cambrian to Recent in age but were never as
common as the articulate brachiopods, which are described below.
Brachiopods belonging to this class have been recorded from several
Paleozoic formations in Texas (Pl. 17, Lingula, Apsotreta, Angulotreta).

55
Plate 17

PENNSYLVANIAN BRYOZOANS

FISTULIPORA × 6
POLYPORA × 5
RHOMBOPORA × 8

CAMBRIAN BRACHIOPODS

APSOTRETA × 10
LINGULA × 4
ANGULOTRETA × 10

MISSISSIPPIAN BRACHIOPODS

RHIPODOMELLA × 1
DICTYOCLOSTUS × 1
CAMAROTOECHIA × 1

56

Fig. 14. Lingula, a typical Recent inarticulate brachiopod showing extended pedicle.

Pedicle
Valve

CLASS ARTICULATA.—
Articulate brachiopods have a well-defined hinge-line (fig. 13a). One valve
has well-developed teeth which articulate with sockets in the opposing
valve, and there is a well-developed muscle system which aids in opening
and closing the shell. Articulate brachiopods are characterized by calcareous
shells which are typically of unequal size and a wide variety of shapes (Pls.
18, 19). The class has been divided into several orders which have been
established primarily on the nature of the pedicle foramen and the nature of
shell growth.

Articulate brachiopods range from Lower Cambrian to Recent in age and are
particularly abundant in certain Pennsylvanian formations of north-central
and Trans-Pecos Texas. They are also present in certain other fossiliferous
strata of Paleozoic age but are less abundant and not as well preserved. The
only Cretaceous brachiopod that is found in large numbers is Kingena
wacoensis (Roemer) (fig. 15), which is particularly abundant in certain
formations in the upper part of the Comanche series.

Fig. 15. Kingena wacoensis, a common Cretaceous brachiopod. (a) Dorsal view. (b) Lateral view.
(c) Ventral view.

Phylum Mollusca

The phylum Mollusca encompasses a large group of aquatic (water-
dwelling) and terrestrial (land-dwelling) invertebrates which includes such
familiar forms as the snails, clams, oysters, squids, and octopuses. Most
mollusks possess a calcareous shell that serves as an exoskeleton, and these
hard parts are well adapted for preservation as fossils. However, some
mollusks (the slugs) have no shells, and others (the squids) have an internal
calcareous shell. Because of their relative abundance and great variety,
mollusks are particularly useful fossils. Moreover, the remains of certain
mollusks, such as the oysters, are important rock builders.

The phylum Mollusca has been divided into five classes:

1. Amphineura—the chitons or sea-mice; shell composed of eight
valves or plates; not a common fossil. Ordovician to Recent.

2. Scaphopoda—the tusk-shells; shell composed of a single tusk-like
valve; generally not a common fossil but locally abundant in
certain Cenozoic formations. Devonian to Recent.

3. Gastropoda—the snails and slugs; slugs are without shells, snails
have a single-valved shell which is typically coiled; common
fossils in Paleozoic, Mesozoic, and Cenozoic rocks. Cambrian to
Recent.

4. Pelecypoda—clams, mussels, oysters, scallops; shells composed of
two valves, usually, but not always, of equal size; common fossils,
especially in Mesozoic and Cenozoic rocks. Cambrian to Recent.

5. Cephalopoda—squids, octopuses, the pearly nautilus, and the
ammonoids (extinct); shell of one valve, usually coiled and
partitioned by septa; valuable fossils, especially in Paleozoic and
Mesozoic rocks. ?Cambrian, Ordovician to Recent.

57
Plate 18
PENNSYLVANIAN BRACHIOPODS

MARGINIFERA × 1
AMBOCOELIA × 1
SQUAMULARIA × 1
DERBYA × 1
MESOLOBUS × 1
CHONETES × 1
LINOPRODUCTUS × 1
PUNCTOSPIRIFER × 1
COMPOSITA SUBTILITA × 1
NEOSPIRIFER × 1

58
Plate 19
PENNSYLVANIAN BRACHIOPODS

JURESANIA × 1
SPIRIFER ROCKYMONTANUS × 1
NEOSPIRIFER CAMERATUS × 1

Of these five classes, only the Gastropoda, Pelecypoda, and 59
Cephalopoda are discussed herein.

CLASS GASTROPODA.—
The typical gastropod has a spirally coiled, single-valved, unchambered
shell. This shell encloses a soft body possessing a well-defined head with a
pair of eyes and one or two pairs of tentacles. Most gastropods have gills and
live in shallow marine waters, but some inhabit fresh water. Others are land-
dwelling forms and breathe by means of lungs.

Gastropod shells, both Recent and fossil, exhibit a great variety of size,
shape, and ornamentation. Such shells may be cone-shaped, spirally coiled,
flat, turreted, or cylindrical. The shell is commonly wound in a spiral around
a central axial pillar (the columella). The closed pointed end of the shell is
called the apex, and each turn of the shell is called a whorl (fig. 16). The
last-formed and largest whorl is called the body whorl, and this whorl
contains the aperture—the opening of the shell. The combined whorls
exclusive of the body whorl are known as the spire. The inner and outer
margins of the aperture are designated the inner lip and the outer lip,
respectively. In some snails the aperture is closed by means of the operculum
—a calcareous or horny plate attached to the foot of the animal. This plate
effectively seals the aperture when the animal is withdrawn into its shell.
Some gastropods have shells that are loosely coiled, and in these forms the
columella is absent. If the whorls of such shells are not in contact on the
inner surface, this leaves an open space which is called the umbilicus (fig.
16a). The umbilicus is commonly seen as an opening in the base of the
gastropod shell, but in some forms the umbilical opening may be partially or
completely covered by a thick growth of shell called the callus.

Many gastropods, particularly those of the Texas Cretaceous, are commonly
preserved as internal or external molds. This type of preservation occurs
after the death of the animal, and the decomposition of the soft parts enables
the shell to become filled with sediment. This filling later becomes
solidified, and the outer shell may eventually be removed by weathering or

solution. This type of internal mold is called a steinkern and normally does
not reflect any external shell characteristics (Pl. 2). In some of the
Pennsylvanian and Tertiary formations, however, gastropods may be
collected with the original shell in an excellent state of preservation.

Plates 20-23 illustrate some typical Paleozoic, Mesozoic, and Cenozoic
gastropods.

CLASS PELECYPODA.—
The pelecypods possess a shell composed of two calcareous valves (fig. 17)
which enclose the soft parts of the animal. Members of this class live
exclusively in an aquatic habitat and are most abundant in marine
environments. Most pelecypods are slow-moving bottom-dwelling forms,
but some, like the oysters, are attached. Still others, for example, the scallop
or Pecten, are swimmers. The Pelecypoda include such familiar saltwater
forms as the clams and oysters, as well as the common fresh-water mussel.
Pelecypods range from Cambrian to Recent in age but are more abundant in
Mesozoic and Cenozoic rocks.

The living animal is aquatic, with well-developed soft parts and a muscular,
commonly hatchet-shaped foot. The soft mantle encloses the body and
secretes the shell, and in some pelecypods part of the mantle is developed
into the incurrent and excurrent siphons. The incurrent siphons bring fresh
water and food into the mantle cavity, and waste products are passed out
through the excurrent siphons. Respiration is by means of gills within the
mantle cavity.

The typical pelecypod valves are of equal size and form, but some, such as
the scallops and oysters, have two valves of unequal size and shape. The
valves are hinged and held together by a tough elastic ligament which runs
along the dorsal (top) side of the shell. In addition to the ligament, 60
most forms have teeth and sockets which are located along the hinge-
line. The teeth in one valve articulate with the sockets in the opposite valve,
and this arrangement gives strength to the hinge.

Fig. 16. Morphology and principal parts of gastropod shells. (a) Low-spired form with
umbilicus. (b) Section of spirally coiled shell showing columella.

a
Suture
Whorl
Body whorl
Aperture

Umbilicus
b
Apex
Spire
Columella
Body whorl
Inner lip
Outer lip

Most of the pelecypod shell is of calcium carbonate, but the outer layer, or
periostracum, of each valve is composed of horny material. The inner
surface of the shell is lined with a calcareous layer of pearly or porcelaneous
material.

61
Plate 20
PENNSYLVANIAN GASTROPODS

STRAPAROLUS × 1
AMPHISCAPHA × 1
WORTHENIA × 1
TREPOSPIRA × 1
BELLEROPHON × 1
EUOMPHALUS × 1

62
Plate 21

PENNSYLVANIAN GASTROPODS

EUPHEMITES × 1
STROBEUS × 1
PLATYCERAS × 1

CRETACEOUS GASTROPODS
INTERNAL MOLDS

GYRODES × 1
LUNATIA × 1
TURRITELLA × 1
CERITHIUM × 1
TYLOSTOMA × 1
NERINEA × 1

63

Plate 22
TERTIARY GASTROPODS

DISTORSIO × 1
MESALIA × 1
FUSUS × 1
COCHLESPIROPSIS × 1
TURRITELLA × 1
LATIRUS × 1
CONUS × 1
VERTAGUS × 1
PSEUDOLIVA × 1

64
Plate 23
TERTIARY GASTROPODS

ANCILLA × 1
ARCHETECTONICA × 1
TUBA × 1
CALYPTRAPHORUS × 1
SYCOSTOMA × 1
SURCULA × 1
VOLUTOLITHES × 1
NEVERITA × 1
LEVIFUSUS × 1

The outline of the shell may vary greatly, but most pelecypods are typically clam-like. However, certain 65
forms are round, others are long and narrow, and some have wing-like structures. Most pelecypods have a
beak which represents the oldest part of the shell. The beak is commonly located on the anterior (front) end of the

shell, and the end of the shell opposite this is designated posterior (the rear). The hinge and ligament are located
dorsally (along the top), and the lower margin of the shell where the valves open is called ventral (fig. 17a).

Fig. 17. Morphology and principal parts of a typical pelecypod shell. (a) Exterior view. (b) Interior view.

a
Dorsal
Beak
Anterior
Posterior
Concentric growth rings
Ventral
b
Hinge teeth
Cardinal teeth
Anterior muscle scar
Posterior muscle scar
Mantle line

The inner surface of the shell has certain markings which, along with the shell form and dentition (the nature 66
and arrangement of the teeth and sockets), are important in classification. Muscle scars are present on the
inside of most valves; the anterior muscle scars are located near the front of the shell, and the posterior muscle
scars are situated near the rear of the shell. These scars mark the place of attachment of muscles which were used
to close the shell and aid in locomotion. Along the ventral margin of some shells there is a line or scar which

extends from the anterior muscle scar to the posterior muscle scar. This is known as the mantle line or pallial line
and marks the place of attachment of the mantle—a soft membranous layer that enclosed the body of the animal.
In some pelecypods the dorsal margin of one valve bears a series of hinge teeth which articulate with a similar set
of sockets on the other valve (fig. 17b). In addition to hinge teeth, certain species have cardinal teeth which are
located below and in front of the hinge teeth.

The exterior of most shells is marked by a series of concentric growth lines (fig. 17a) which mark points of
periodic addition of shell material. The external surface of many shells is also marked by various types of
ornamentation, such as ribs, nodes, spines, and grooves.

Fossil collectors commonly find only one valve of the pelecypod shell. This is because the shell normally opens
when the animal dies, and the valves may easily become separated. Fossil pelecypods are also commonly
preserved as external and internal molds, and these are found in fossiliferous strata of almost all ages. Some
pelecypods of Pennsylvanian, Mesozoic, and Cenozoic age are found with original shell material that appears to
have undergone very little change. Fossil pelecypods are abundant and varied in Texas and are found in most of the
fossiliferous formations of the Pennsylvanian, Cretaceous, and Tertiary systems (Pls. 24-31).

CLASS CEPHALOPODA.—
These are marine mollusks with or without chambered or solid shells which may be internal or external. The living
animal possesses a well-developed head with eyes, horny jaws, and many tentacles fused with the foot.
Cephalopods are the most advanced of all mollusks and include the squid, octopus, pearly nautilus, and the extinct
ammonoids. Members of this class range from Cambrian to Recent in age but were much more abundant in ancient
seas than they are today. Their remains constitute a very useful group of fossils, particularly in Paleozoic and
Mesozoic rocks.

Most paleontologists have divided the Cephalopoda into three subclasses, the Nautiloidea, Ammonoidea, and the
Coleoidea (known also as subclass Dibranchiata and subclass Decapoda); each of these is discussed below.

Subclass Nautiloidea.—
The nautiloids are cephalopods with external chambered shells in which the septa (dividing partitions) are simple
and have smooth edges. This subclass is represented by a single living genus, Nautilus, and a large number of
fossil forms.

In the living Nautilus the shell is composed of calcium carbonate and is coiled in a flat spiral (fig. 18). The interior
of the shell is divided into a series of chambers by calcareous partitions called septa. The point where each septum
joins the inner surface of the shell is known as the suture. These suture lines (fig. 19a) are not visible from the
outside unless the outer shell has been removed, but they are visible on the internal molds of many fossil
cephalopods and are of great importance in nautiloid and ammonoid classification. Nautiloids have very simple
smoothly curved suture patterns, but ammonoids are characterized by more complex and wrinkled sutures (fig.
19d).

Although the shell of the only type of living nautiloid is coiled, many of the early forms had straight cone-shaped
shells (Orthoceras, Pl. 32), and these are common in some of the Pennsylvanian formations of Texas. Fossil coiled
nautiloids may be collected in certain of the Cretaceous and Tertiary strata of the State, but their remains are not
common. Cymatoceras (Pl. 32) is a coiled fossil nautiloid from the Cretaceous of north Texas.

67
Plate 24
PENNSYLVANIAN PELECYPODS

SCHIZODUS × 1
MYALINA × ½
ASTARTELLA × 1
NUCULOPSIS × 1
ALLORISMA × 1
NUCULANA × 1
YOLDIA × 1
PINNA × ½

68

Plate 25
CRETACEOUS PELECYPODS

PROTOCARDIA × 1
ALECTRYONIA LUGUBRIS × 1
PLICATULA × 1
PECTEN × 1

69
Plate 26
CRETACEOUS PELECYPODS

GRYPHAEA WASHITAENSIS × 1
GRYPHAEA GRAYSONANA × 1
INOCERAMUS × 1
TRIGONIA × 1

70
Plate 27
CRETACEOUS PELECYPODS

EXOGYRA ARIETINA × 1
EXOGYRA LAEVISCULA × 1
NEITHEA × 1
EXOGYRA PONDEROSA × 1
EXOGYRA TEXANA × 1

71
Plate 28
CRETACEOUS PELECYPODS

PACHYMYA × ½
OSTREA CARINATA × 1
OSTREA QUADRIPLICATA × 1
PHOLADOMYA × 1

72
Plate 29
TERTIARY PELECYPODS

LIMA × 1
OSTREA LISBONENSIS × 1
PITAR × 1
VENERICARDIA BULLA × 1
PACHECOA × 2
PHOLADOMYA × 2
OSTREA SELLAEFORMIS × 1
CRASSATELLA × 1

73
Plate 30
TERTIARY PELECYPODS

ORTHOYOLDIA × 1
TELLINA × 1
VOKESULA × 2
NUCULA × 2
VENERICARDIA × ½

74
Plate 31
TERTIARY PELECYPODS

PLICATULA × 1
PECTEN × 1
ANOMIA × 1
GLYCYMERIS × 2
CARYOCORBULA × 2
BARBATIA × 1

75

Fig. 18. Morphology and principal parts of the pearly nautilus. (a) Exterior view of a Recent shell. (b) Sectioned view of the same shell to show
internal structures.

b
Living chamber
Aperture
Septa
Siphuncle
Protoconch
Chamber

Fig. 19. Characteristic features of the various types of cephalopod sutures. (a) Nautiloid type. (b) Goniatite type. (c) Ceratite type. (d) Ammonite
type.

Subclass Ammonoidea.—
The ammonoids are a group of extinct cephalopods which are related to the nautiloids but are characterized by
more complex suture patterns. Members of this subclass have an external partitioned shell which is straight,
curved, or spirally coiled (Pl. 33). This group of cephalopods first appeared in Devonian time, became extremely
abundant and varied during the Mesozoic, and was extinct by the end of the Cretaceous period.

Most Paleozoic ammonoids are characterized by a combination curved and angular suture pattern, and this type of
suture pattern is referred to as goniatitic (fig. 19b). Sutures that are curved and crenulated (marked in places by a
series of tooth-like indentations) are known as ceratitic (fig. 19c). Ceratitic sutures first appeared in the
Mississippian, became increasingly abundant during the Triassic but were much less abundant during the
Cretaceous. The ammonitic suture has a very complexly subdivided pattern (fig. 19d). Cephalopods with
ammonitic sutures range from Pennsylvanian to Cretaceous in age and were the most abundant cephalopods of the
Mesozoic.

76
Plate 32

PENNSYLVANIAN CEPHALOPODS

PHANEROCERAS × 1
ORTHOCERAS × 1

CRETACEOUS CEPHALOPODS

METOICOCERAS × ½
CYMATOCERAS × ½

77
Plate 33
CRETACEOUS CEPHALOPODS

TEXANITES × ½
ACANTHOCERAS × ½
TURRILITES × ½
DUFRENOYIA × ½
OXYTROPIDOCERAS × ½
BACULITES × ½
BELEMNITE × ½

Ammonoids are locally abundant in many of the fossiliferous rocks of Texas and are among the more useful 78
Mesozoic guide fossils. Goniatites may be found in the Pennsylvanian of north-central and Trans-Pecos
Texas, and ammonoids with the ceratitic suture pattern can be collected from the Lower Cretaceous of many parts
of the State. Cephalopods exhibiting the typical ammonitic suture pattern are abundant in many of the Cretaceous
rocks of Texas, and these fossils have contributed much toward an understanding of the Cretaceous strata of this
State.

Subclass Coleoidea.—
These are squid-like cephalopods characterized by an internal shell or no shell at all. Included in this group are the
squids, cuttlefish, octopuses, and the extinct belemnoids, but of these only the belemnoids are useful fossils.
Members of this subclass range from Mississippian to Recent in age.

Order Belemnoidea.—
The belemnoids appear to be the oldest and most primitive of the coleoid cephalopods. Their earliest known
occurrence is in rocks of Mississippian age, and they were particularly abundant during the Mesozoic. They
became extinct at the end of Cretaceous time but have left considerable evidence of their existence in the Mesozoic
strata of many parts of the world. Certain forms, because of their abundance and relatively short geologic range,
are excellent guide fossils. Belemnoids have been found in the Upper Cretaceous of Texas (Pl. 33) but in general
are rare or unknown in most Texas formations.

Phylum Annelida

Members of the phylum Annelida include the segmented worms such as the common earthworm. Annelids are
marine, fresh water, or terrestrial and have apparently been common through much of geologic time. Because of
their lack of hard parts, most of these worms have left little direct fossil evidence of their activities in the geologic
past. Some annelids secrete straight or coiled calcareous tubes, and fossil worm tubes of this sort (fig. 20) are
commonly found attached to brachiopods, mollusks, and other objects. Tubes of this nature have been reported
from Paleozoic, Mesozoic, and Cenozoic rocks in Texas.

Fig. 20. Types of typical annelid worms. (a) Serpula (×1) (b) Hamulus (×2). (c) Spirobis (×15).

Some annelids have small chitinous jaws and teeth which also may be preserved as fossils. These dental structures
are called scolecodonts and are microfossils.

Phylum Arthropoda

The arthropods are one of the more advanced groups of invertebrates, and they are known from the Cambrian to
the Recent (Pl. 34). Modern representatives of this group include the crabs, shrimp, crayfish, insects, and spiders.
Arthropods vary greatly in size and shape and are among the most abundant of all animals. They have become
successfully adapted to a wide variety of environments and live on land, in water, and in the air. The typical
arthropod has a segmented body which is usually covered by a chitinous exoskeleton which, in some forms,
contains additions of calcium carbonate. They are highly specialized and well-developed animals in which
locomotion is by means of paired jointed appendages.

Although the arthropods are of great importance in nature today, only a few groups are of importance to the
paleontologist. Only two of these, the trilobites and the ostracodes, are discussed herein.

Subphylum Trilobitomorpha

The members of this subphylum are extinct arthropods which were most abundant during early Paleozoic time.

CLASS TRILOBITA.—
The trilobites are a group of exclusively marine arthropods which derive their name from the typical three-lobed
appearance of their bodies (fig. 21a). The trilobite body is divided into a central or axial lobe and two lateral

lobes. The body of the animal was encased in a chitinous exoskeleton. The top part of this exterior covering, the
carapace, is very thick, and it is this part of the trilobite that is usually preserved.

79
Plate 34
FOSSIL ARTHROPODS

FOSSIL INSECT × 1
FOSSIL CRUSTACEANS
ENOPLOCLYTIA × 1⅓
ASTACODES × ¾
NOTOPOCORYSTES × 2
OSTRACODES × 40

80

Fig. 21. Morphology and principal parts of trilobites.

Cephalon
Thorax
Pygidium
Axial lobe
Lateral lobes

The body is also divided into three parts from front to back. Beginning at the front of the animal these divisions are
the cephalon or head, the thorax or abdomen, and the pygidium or tail (fig. 21a). The body segments of the thorax
were arranged in such a manner as to permit the animal to roll up into a ball, and many trilobites are found in this
position (fig. 21b).

Trilobites first appeared in the Cambrian and were extinct by the end of the Permian. They occur sparingly in
certain of the Paleozoic rocks of Texas and when found are likely to be fragmental and in a poor state of
preservation.

Subphylum Crustacea

The crustaceans are the crabs, shrimp, crayfish, and ostracodes. Although not abundant, fossil crabs have been
described from certain Cretaceous and Tertiary formations of the State (Notopocorystes, Pl. 34). However, the
most useful and abundant crustacean fossils are the members of the class Ostracoda.

CLASS OSTRACODA.—
The ostracodes are small, bivalved, aquatic crustaceans which have the external appearance of small clams (Pl.
34). The remains of these tiny animals are so small that they are best studied under a low-power microscope, and
because of their small size they are particularly useful to the micropaleontologist.

Fossil ostracodes range from Ordovician to Recent in age and have been recorded in the Paleozoic, Mesozoic, and
Cenozoic rocks of Texas. Their remains are particularly abundant in certain of the Cretaceous and Tertiary marine
formations of the State.

Phylum Echinodermata

The echinoderms are a large group of exclusively marine animals, most of which exhibit a marked five-fold radial
symmetry (Pls. 35, 36). Living echinoderms have well-developed nervous and digestive systems, a distinct body
cavity, and are a relatively complex group of organisms.

The typical echinoderm has a skeleton composed of numerous calcareous plates which are intricately fitted
together and covered by a leathery outer skin (the integument). The echinoderm body often exhibits a typical star-
shaped form, but some types may be heart-shaped, biscuit-shaped, or cucumber-shaped.

Members of this phylum range from Cambrian to Recent in age and are abundant as fossils in many of the marine
formations of Texas.

The phylum Echinodermata has been divided into two subphyla, the Pelmatozoa (those forms that were attached to
sea floor by a stem or a stalk) and the Eleutherozoa (the stemless unattached echinoderms). 81

Subphylum Pelmatozoa

These are echinoderms which are more or less permanently attached to the bottom of the sea by means of a stalk
which is composed of slightly movable, calcareous, disk-like segments (fig. 23).

Pelmatozoans range from Cambrian to Recent in age, and their fossilized remains are particularly abundant in
Paleozoic rocks. The subphylum has been divided into several classes, but only three of these, the Cystoidea,
Blastoidea, and Crinoidea, are discussed here. With the exception of the Crinoidea, all of the attached echinoderms
are extinct.

CLASS CYSTOIDEA.—
These are primitive attached echinoderms which were relatively common in early Paleozoic time. The typical
cystoid has a somewhat globular or sac-like calyx (the main body skeleton) composed of numerous, irregularly
arranged, calcareous plates (fig. 22b). The plates composing the calyx are usually perforated by pores or slits
which were probably used in excretion or respiration. The calyx was attached to the sea bottom by a short stem.

Cystoids range from Cambrian to Devonian in age and were especially abundant during Ordovician and Silurian
time. Their remains are rare or absent in the rocks of Texas.

Fig. 22. Two extinct attached echinoderms. (a) Pentremites (Mississippian). (b) Caryocrinites (Silurian).

CLASS BLASTOIDEA.—
The blastoids are extinct short-stemmed echinoderms with a small, symmetrical, bud-like calyx. The blastoid calyx
is composed of 13 calcareous plates arranged in a typical five-sided pattern (fig. 22a). The mouth is located in the

center of the calyx and is surrounded by five openings called spiracles. Five distinct ambulacral or food grooves
radiate outward from the mouth.

Blastoids range from Ordovician to Permian in age and were especially abundant during the Mississippian period.
No blastoids have been reported from any of the rocks of Texas.

CLASS CRINOIDEA.—
The crinoids are commonly called sea-lilies because of their flower-like appearance. The calyx is composed of
symmetrically arranged calcareous plates, and most crinoids have a long stem. Other crinoids are free-swimming
in the adult stage and are attached only during the earlier phases of their development.

The crinoid calyx is typically cup-shaped (fig. 23) and five grooves radiate out from its center. These grooves
continue outward along the complexly segmented arms and are used as channels to convey food to the mouth.

Fig. 23. Typical modern crinoid, or “sea lily,” showing principal parts.

Calyx
Arm
Plate
Stem
Columnal
Cirri
Holdfast (root)

The crinoid stem is attached to the base of the calyx and serves for purposes of support and attachment. This 82
stem consists of a relatively long flexible stalk composed of numerous calcareous disk-shaped segments
called columnals (fig. 23; Pl. 35), each of which contains a round or star-shaped opening in its center. Many
crinoids have very long stalks (some are as much as 50 feet in length), and when the animal dies the columnals
become separated and are scattered about on the ocean floor. Many Paleozoic limestones contain such great

numbers of crinoid columnals that they are referred to as crinoidal limestones (fig. 8). Crinoidal limestones occur
in some of the Mississippian and Pennsylvanian formations of central Texas and in the Pennsylvanian of north-
central and Trans-Pecos Texas.

The stalk is attached to the sea floor or some other object by means of a root system called the holdfast (fig. 23).
This structure commonly branches out into the surrounding sediments, and in this manner the crinoid animal is
firmly anchored to the bottom of the sea.

Crinoids, like most echinoderms, are gregarious animals—that is, they commonly live together in large numbers,
and for this reason great numbers of crinoid remains are commonly found concentrated in relatively small local
areas. Most fossil crinoids are found as stem fragments because the more fragile calyx and root system are less
likely to be preserved.

The earliest known crinoids have been found in rocks of Ordovician age, and their remains are particularly
abundant in Paleozoic rocks. Crinoids are living today but most of them are stemless free-swimming forms called
“feather stars,” much less abundant than their Paleozoic ancestors.

Subphylum Eleutherozoa

The eleutherozoans are free-swimming, bottom-dwelling, echinoderms which have been divided into two classes.
The class Asterozoa (star-shaped echinoderms) contains the subclasses Asteroidea (the starfishes) and the
Ophiuroidea (the brittle stars). Although they are known as fossils, neither of these groups is of paleontological
importance. The class Echinozoa (echinoderms without laterally directed arm-like extensions) contains the
subclasses Echinoidea (the sea urchins and sand dollars) and Holothuroidea (the sea cucumbers). Of these two
subclasses, only the Echinoidea are useful fossils.

CLASS ASTEROZOA.—
These are typical star-shaped free-moving echinoderms in which the body is divided into a central disk and
radiating arms.

Subclass Asteroidea.—
This class contains the starfishes which, although not common fossils, illustrate well the typical echinoderm
characteristics (Pl. 35). Fossil starfishes have been found sparingly in certain formations in Texas, but well-
preserved specimens are quite rare. However, excellently preserved starfishes have been found in slabs of
Cretaceous limestones from central and north-central Texas.

Subclass Ophiuroidea.—
The ophiuroids are echinoderms with a well-defined central disk and five long, slender, whip-like arms. They have
been called brittle stars because of their ability to shed their arms when they are disturbed. Their long, slender,
snake-like arms have also resulted in their being called serpent stars. Ophiuroids range from Ordovician to Recent
in age, but because of the delicate nature of their bodies they are seldom found as fossils. Ophiuroid remains have
been found in certain Mesozoic and Cenozoic rocks of Texas, but they consist largely of small segments of the
arms or body fragments.

CLASS ECHINOZOA.—
The echinozoans are a group of unattached echinoderms whose bodies consist of numerous calcareous plates and
spines, but they do not possess the radiating arm-like extensions which characterize the asterozoans.

Subclass Echinoidea.—
Echinoids are free-moving echinoderms with disk-shaped, heart-shaped, biscuit-shaped, or globular exoskeletons
(Pl. 36). Modern representatives of this group include the familiar sea urchins, heart urchins, and the sand dollars.

83
Plate 35

CRINOIDS
CRINOID CALYX × ½
CRINOID COLUMNALS × 1
HOLOTHURIAN SCLERITES (GREATLY ENLARGED)
CRETACEOUS FOSSIL STARFISHES
PENTAGONASTER × 1
PENTACEROS × 1

84
Plate 36
CRETACEOUS ECHINOIDS

SALENIA × 1
ECHINOID SPINES × 2
ECHINOID PLATE × 2
HEMIASTER × 1
HOLASTER × 1
HOLECTYPUS × 1

The echinoid test (exoskeleton) is composed of many intricately fitting calcareous plates (Pl. 36) which 85
enclose the animal’s soft parts. The exterior of the test is typically covered with large numbers of movable
spines (Pl. 36) which vary greatly in size. These spines are of some aid in locomotion, support the skeleton of the
animal, and provide a measure of protection from enemies.

The oldest known echinoids have been recorded from rocks of Ordovician age, but it was not until the Mesozoic
that the group began to flourish. They were especially abundant during the Cretaceous and have been abundant and
varied from that time until the present.

Echinoids are particularly numerous in many of the Lower Cretaceous formations of Texas where they are
commonly found in an excellent state of preservation. Heart urchins and biscuit urchins may be found in large

numbers in many areas of the State, and especially in areas where there are good exposures of fossiliferous Lower
Cretaceous rocks.

Subclass Holothuroidea.—
Members of this class, commonly called sea cucumbers, have a rather elongate, sac-like, cucumber-shaped body
and bear little resemblance to other members of the phylum Echinodermata. The sea cucumbers do not have a
well-defined skeleton; rather the body is supported by many small, disconnected, calcareous plates or rods called
ossicles or sclerites (Pl. 35). These minute structures are embedded in the leathery skin which covers the body of
the sea cucumber and may be preserved as fossils. Such remains are locally abundant in certain formations in
Texas, but because of their small size, scattered occurrence, and problems in classification, this group is of little
use to most paleontologists.

Holothuroid body impressions have been reported from the Middle Cambrian, and sclerites from rocks as old as
Mississippian.

Phylum Chordata

The chordates are the most advanced of all animals and are characterized by the presence of a well-developed
nervous system and a body supported by a bony or cartilaginous notochord and/or spinal column. In the higher
chordates (the vertebrates) the notochord is normally replaced by bone, but in the lower chordates (for example,
the graptolites) it remains in a cartilaginous condition.

The phylum Chordata contains only two subphyla of paleontological significance. These are the subphylum
Hemichordata, composed of primitive chordates (including the graptolites which are important fossils), and the
Vertebrata, which includes all animals with backbones.

Subphylum Hemichordata

The hemichordates are characterized by a well-defined notochord which runs the length of the body, but they do
not possess a true backbone. Only one class, the Graptolithina, is of paleontological importance.

CLASS GRAPTOLITHINA.—
The graptolites are a group of extinct colonial animals which were very abundant during early Paleozoic time.
They are characterized by a chitinous exoskeleton consisting of rows of cups or tubes which housed the living
animal. These cups are attached to single or branching stalks (fig. 24) which in some forms were attached to sea
weeds, rocks, or other foreign objects where they led a fixed existence. The stalks of the unattached graptolites
grew on floats (fig. 24a) and these floating forms attained wide geographic distribution. It is also possible that
some of the attached forms were fixed to floating objects, such as sea weed, and thus were distributed in this
manner.

Previous classifications have recognized the graptolites as members of the phylum Coelenterata. As coelenterates
they were assigned, at various times, to the classes Hydrozoa, Scyphozoa, and Graptozoa. In addition, they were
also classified as bryozoans by certain of the early paleontologists. This publication, in keeping with recent
changes in taxonomy, considers graptolites to be an extinct group of hemichordates. This classification is based
upon research in which uncompressed graptolites were etched out of chert and studied in great detail. 86
Information derived from these relatively undistorted specimens indicates a much higher degree of body
organization than was previously suspected, and as a result of these studies most paleontologists now consider
graptolites to be some form of primitive chordate.

Fig. 24. Graptolites. (a) Diplograptus (×2). (b) Dendrograptus (×3). (c) Phyllograptus (×2).

The chitinous graptolite exoskeleton is commonly preserved as a flattened carbon residue; their remains may be
locally abundant along the bedding planes of certain black or dark gray shales.

Graptolites are known from rocks that range from Cambrian to Mississippian in age, and they are among the most
important guide fossils for Ordovician and Silurian rocks.

Graptolites have been reported from Cambrian rocks in central Texas and from the Ordovician of west Texas (fig.
24). The most abundant of these occur in certain Ordovician rocks in the Trans-Pecos area where they are common
fossils in certain formations.

Subphylum Vertebrata

The vertebrates are the most advanced of all chordates. They are characterized by a skull and a bony or
cartilaginous internal skeleton, with a vertebral column of bone or cartilage. This subphylum is commonly divided
into two superclasses, the Pisces (the fishes and their relatives) and the Tetrapoda (the four-footed animals).

As mentioned earlier, most amateur collectors collect very few vertebrate remains, and for this reason this group is
not discussed in detail. However, the more important vertebrate classes are briefly reviewed to enable the reader to
have some understanding of this important group of animals. This part of the handbook will also serve as an
introduction to some of the interesting and unusual, but now extinct, animals that have inhabited Texas in the
geologic past. Among these animals are giant fishes, primitive amphibians, and many different types of dinosaurs.
Included also are such unusual mammals as the giant ground sloths, saber-tooth cats, mammoths, and 87
mastodons, all of which are now extinct. The remains of these, and many other interesting extinct vertebrates,
may be seen in the geological collections of the Texas Memorial Museum at Austin. Many of these displays are
accompanied by drawings which depict the scientific restoration of the animal’s soft parts and show how the
animal may have appeared in life.

Superclass Pisces

The members of this superclass are commonly called fishes and are the simplest and most numerous of all
vertebrates. They are aquatic, free-moving, cold-blooded (their blood maintains the temperature of the surrounding
water), and breathe primarily by means of gills. However, some forms (the lungfishes) breathe by means of a lung
developed from the air-bladder.

The most recent fish classification recognizes four major classes, the Agnatha (primitive jawless fishes), the
Placodermi (armored fishes with primitive jaws), the Chondrichthyes (sharks and related forms with cartilaginous

internal skeletons), and the Osteichthyes (true bony fishes).

CLASS AGNATHA.—
Fishes belonging to this class are primitive, jawless, and represented by the living lampreys and hagfishes. The
first agnathans appeared in the Ordovician and were armored by a bony covering on the front part of their bodies.
These primitive fishes, called ostracoderms, are the earliest recorded fishes and, in addition, appear to be the first
known vertebrate animals. The ostracoderms first appeared in late Ordovician time, increased in numbers in the
Silurian, and were extinct by the end of the Devonian.

CLASS PLACODERMI.—
These are primitive jaw-bearing fishes, the majority of which were heavily armored (Pl. 37). The placoderms were
shark-like in appearance, and some of them grew to be as much as 30 feet in length. Members of this class
appeared first in the Devonian and lasted into the Permian, at which time they became extinct. Placoderms are rare
in Texas, but the fragmentary remains of these primitive fishes have been found in Devonian rocks in central
Texas.

CLASS CHONDRICHTHYES.—
This class includes such modern forms as the sharks, rays, and skates. They are characterized by skeletons which
are composed of cartilage and are very abundant in the marine waters of today. The earliest known representatives
of this class are reported from rocks of Devonian age, and they have been relatively common up to the present
time.

Shark teeth (Pl. 37) can be found in Texas in Pennsylvanian, Permian, Cretaceous, Paleocene, Eocene, and
Miocene rocks. These are probably the most common vertebrate fossils to be found in Texas and are usually found
in thin-bedded marine limestones or clays.

CLASS OSTEICHTHYES.—
The Osteichthyes includes the true bony fishes, which are the most highly developed and abundant of all fishes.
They possess an internal bony skeleton, well-developed jaws, an air-bladder, and, typically, an external covering of
overlapping scales.

Included in this class are a primitive group of fishes called crossopterygians. These were very abundant in the
Devonian and are believed to be the ancestors of the amphibians. The modern lungfishes also belong to the class
Osteichthyes, and these primitive fishes, which are now found only in Australia, South America, and Africa,
breathe by means of gills and lungs which have been developed from the air-bladder. Although not abundant as
fossils, the remains of these specialized fishes have added much to present knowledge concerning the development
of certain of the higher vertebrates.

The remains of bony fishes have been collected at many localities in Texas, and fossils of this type have been
found primarily in rocks of Cretaceous age but have been reported from other rocks as well. Fish fossils are more
commonly found in the form of teeth (Pl. 37), vertebrae, scales, and an occasional well-preserved skeleton.

88
Plate 37

SHARK TEETH × 1

CONODONTS
(GREATLY ENLARGED)

PRIMITIVE ARMORED FISH
PLACODERM (DEVONIAN)
×½

Conodonts (Pl. 37) are small, amber-colored, tooth-like fossils which are believed to represent the teeth of 89
some type of extinct fish. Although geologists do not know a great deal about the origin of these strange
fossils they are of value in micropaleontology. Conodonts have been reported from several Paleozoic formations in
Texas and are useful guide fossils in some areas.

Superclass Tetrapoda

The tetrapods are the most advanced chordates and are typified by the presence of lungs, a three- or four-
chambered heart, and paired appendages. Included here are the classes Amphibia (frogs, toads, and salamanders),
Reptilia (lizards, snakes, turtles, and the extinct dinosaurs), Aves (birds), and Mammalia (including the mammals,
such as men, dogs, whales, etc.).

CLASS AMPHIBIA.—
The amphibians were the earliest developed four-legged animals and are represented by such living forms as the
toads, frogs, and salamanders. Amphibians are cold-blooded animals that primarily breathe by lungs and spend
most of their life on land, but during their early stages of development they live in the water where they breathe by
means of gills.

The amphibians apparently developed from the crossopterygian fishes during late Devonian time and were
relatively abundant in the Pennsylvanian, Permian, and Triassic.

Amphibian remains in Texas are confined largely to lower Paleozoic and upper Mesozoic rocks. Numerous
interesting and important discoveries of fossil amphibians have been made in north and west Texas where their
remains (Pl. 40) have been collected in association with early types of reptiles. The areas where Permian red beds
are exposed in Archer and Baylor counties and where Triassic red beds are exposed from Big Spring north along
the edge of the High Plains have furnished most of these specimens.

CLASS REPTILIA.—
The reptiles have become adapted to permanent life on land and need not rely on an aquatic environment. They are
cold-blooded and are normally characterized by a scaly skin. Reptiles have been much more abundant in the past
than they are today, and they assumed many different shapes and sizes in the geologic past. Modern classifications
recognize a large number of reptilian groups, but only the more important of these are briefly reviewed here.

Cotylosaurs.—
These were a group of primitive reptiles which, although retaining some amphibian characteristics, became
adapted to an exclusively land-dwelling existence. The cotylosaurs lived during the Pennsylvanian and Permian

and apparently became extinct sometime during the late Permian. Cotylosaurs (Pl. 40) are well known from the
Permian of north Texas.

Turtles.—
These are reptiles in which the body is more or less completely enclosed by bony plates. This group is first known
as fossils from late Triassic rocks of Europe, and modern representatives of the group include the turtles and
tortoises. Fragmentary remains of turtle shells are among the most common vertebrate fossils found in the Tertiary.
Some of the late Tertiary land tortoises were 3 to 4 feet long. The earliest known turtles in Texas have been found
in Cretaceous rocks.

Pelycosaurs.—
The pelycosaurs were a group of late Paleozoic reptiles some of which were characterized by the presence of a tall
fin on their back (Pl. 40). The fossils of these unusual creatures are well known from the Permian red beds of
north-central Texas.

Therapsids.—
The therapsids were a mammal-like group of reptiles which were well developed for a terrestrial existence.
Although the remains of these primitive reptiles are not particularly important fossils, study of the therapsids has
provided much valuable information about the origin of the mammals. Members of this group appeared first in the
middle Permian and persisted until the middle Jurassic, but therapsid remains have not been reported from Texas.

90
Plate 38
Comparison of the dinosaurs. Reproduced with permission of Dr. J. W. Dixon, Jr., and Geology Department, Baylor University,
Waco, Texas.

DINOSAUR SAURISCHIANS ORNITHISCHIANS
STOCKS
DINOSAUR THEROPOD SAUROPOD ORNITHOPOD STEGOSAUR CERATOP
TYPES
POSTURE BIPEDAL QUADRUPEDAL BIPEDAL AND QUADRUPEDAL QUADRU
QUADRUPEDAL
ARMOR UNARMORED UNARMORED UNARMORED (SPEED BONY PLATES HORNS, B
EXCEPT FOR WAS CHIEF ALONG BACK, PLATE OV
HUGE SHARP DEFENSE) SPIKED-TAIL
TEETH
DIET CARNIVOROUS HERBIVOROUS HERBIVOROUS HERBIVOROUS HERBIVO
OTHER LARGE HEAD HUGE BODY, SLENDER-BUILD, SHORT NECK, SHORT N
DESCRIPTIVE WITH POWERFUL LONG NECK AND “DUCK-BILLED” LONG TAIL, STOCKY
REMARKS JAW, GREATLY TAIL, SMALL SMALL HEAD
REDUCED FORE- HEAD
LIMBS
EXAMPLES CERATOSAURUS- BRACHIOSAURUS- PARASAUROLOPHUS- STEGOSAURUS- STYRAC
(AND AGE) J J K J K
J-JURASSIC ALLOSAURUS-J DIPLODOCUS-J CORYTHOSAURUS-K PROTOCE
K- TYRANNOSAURUS- BRONTOSAURUS-J TRACHODON-K K
CRETACEOUS K TRICERA
SCALE IN 10 10 5 5 5
FEET
91
Plate 39
Comparison of Mesozoic flying and swimming reptiles. Reproduced with permission of Dr. J. W. Dixon, Jr., and Geology
Department, Baylor University, Waco, Texas.

FLYING REPTILES—PTEROSAURS

GROUP AGE TEETH TAIL HEAD SIZE EXAM
RHAMPHORHYNCHOIDS JURASSIC WELL LONG TAIL WITHOUT SMALL RHAMPHOR
DEVELOPED WITH CREST MAXIMUM
FLATTENED WINGSPAN
RUDDER AT OF 2 FEET
END
PTERODACTYLOIDS JURASSIC JAW PARTLY SHORT OR WITH FROM PTERANOD
AND OR NO TAIL SMALL SIZE OF
CRETACEOUS COMPLETELY OR SPARROW
TOOTHLESS, LARGE TO
HORNEY CREST GIANTS
BEAK WITH
SPAN OF
25′

MESOZOIC SWIMMING REPTILES

GROUP AGE DESCRIPTION SIZE HABITAT EXAMPLE
ICHTHYOSAUR TRIASSIC TO FISH-LIKE BODY, AVERAGE MARINE ICHTHYOSAURUS-J
CRETACEOUS HEAD LONG AND LENGTH =
POINTED, NO 7′
DISTINCT NECK MAXIMUM
LENGTH =
43′
MOSASAUR CRETACEOUS LIZARD-LIKE AVERAGE MARINE PYLOSAURUS
BODY, FLATTENED LENGTH =
TAIL, DOUBLE- 15′-20′
JOINTED JAW, MAXIMUM
RECURVED TEETH LENGTH =
50′
PLESIOSAUR TRIASSIC TO LONG NECK AND MAXIMUM MARINE ELASMOSAURUS-K
CRETACEOUS SMALL HEAD OR LENGTH = TRINACROMERUM-
LONG HEAD AND 50′ K
SHORT NECK,
POWERFUL
FLIPPERS
CHELONIA TRIASSIC TO SHAPED LIKE MAXIMUM MARINE, ARCHELON-K
(TURTLES) PRESENT MODERN SIZE = 11′ × STREAMS, AND
TURTLES, BODY 12′ TERRESTRIAL
COVERED WITH
BONY PLATES
PHYTOSAUR TRIASSIC CROCODILE-LIKE MAXIMUM STREAMS AND RUTIODON
BODY, NOSTRILS LENGTH = SWAMPS
ON A “HUMP” 25′
ALMOST
BETWEEN THE
EYES
92
Plate 40

PELYCOSAUR × ¹/₁₂
DIMETRODON
PRIMITIVE AMPHIBIAN × ¹/₂₀
ERYOPS
COTYLOSAUR
SEYMOURIA × ⅕

93
Plate 41
SWIMMING REPTILES

ICHTHYOSAUR × ¹/₁₂₀
MOSASAUR × ¹/₆₀
PLESIOSAUR × ¹/₆₀

94
Plate 42

CROCODILE-LIKE REPTILE
× ¹/₅₀
PHYTOSAUR

FLYING DINOSAURS

RHAMPHORHYNCHUS × ⅙
PTERANODON × ¹/₄₀

Ichthyosaurs.— 95
These were extinct, short-necked, marine reptiles that were fish-like in appearance. Ichthyosaurs resemble
the modern dolphins, and some of them attained lengths of 25 to 40 feet (Pl. 41), though the average was much
less. The group is known from rocks ranging from middle Triassic to late Cretaceous in age.

Mosasaurs.—
The mosasaurs are another group of extinct marine lizards which lived in Cretaceous seas. Some of these great
reptiles grew to be as much as 50 feet long, and their great gaping jaws were filled with many sharp recurved teeth
(Pl. 41). Mosasaurs were present in the great Cretaceous seas which covered many parts of Texas, and their
remains have been reported from both north and central Texas. One such skeleton was found near Austin, and its
skull is on display in the Texas Memorial Museum.

Plesiosaurs.—
The plesiosaurs were marine reptiles which were characterized by a broad turtle-like body, paddle-like flippers,
and a long neck and tail (Pl. 41). These reptiles were not as streamlined or well equipped for swimming as the
ichthyosaurs or mosasaurs, but the long serpent-like neck was probably very useful in helping the reptile catch fish
and other small animals for food. Plesiosaur remains range from middle Triassic to late Cretaceous in age, and they
have been found in Cretaceous rocks in Texas. A short-necked plesiosaur which was collected from Upper
Cretaceous rocks near Waco is on display in the Strecker Museum at Baylor University in Waco.

Phytosaurs.—
The phytosaurs were a group of crocodile-like reptiles which ranged from 6 to 25 feet in length (Pl. 42). They
resembled the crocodiles both in appearance and in their mode of life, but this similarity is only superficial, and the
phytosaurs and crocodiles are two distinct groups of reptiles.

The phytosaurs are exclusively Triassic in age and their remains have been collected from Triassic rocks along the
eastern margin of the High Plains of Texas.

Crocodiles and alligators.—
These reptiles adapted themselves to the same type habitat that was occupied by the phytosaurs, which preceded
them. Crocodiles and alligators were much larger and more abundant during Cretaceous and Cenozoic time than
they are today; the crocodiles first appeared in the Cretaceous and the alligators in the Tertiary. The remains of
both crocodiles and alligators have been found in Texas, and one such crocodile (Phobosuchus) represents the
remains of the largest crocodile yet discovered (Pl. 43). This specimen probably had an overall length of 40 to 50
feet, and its massive skull was 6 feet long and possessed exceptionally strong jaws. The remains of this great beast
were collected from exposures of Upper Cretaceous rocks along the Rio Grande in Trans-Pecos Texas.

Pterosaurs.—
These were Mesozoic reptiles with bat-like wings supported by arms and long thin “fingers” (Pl. 42). The
pterosaurs were well adapted to life in the air, and their light-weight bodies and wide skin-covered wings enabled
them to soar or glide for great distances. The earliest known pterosaurs were found in lower Triassic rocks, and the
group became extinct by the end of the Cretaceous. During this time certain of these creatures attained a
wingspread of as much as 27 feet, but their bodies were small and light.

Dinosaurs.—
The collective term “dinosaurs” (meaning terrible lizards) has been given to that distinctive group of reptiles
prominent in Mesozoic life for some 140 million years. In size, the dinosaurs ranged from as little as 1 foot to as
much as 85 feet in length and from a few pounds to perhaps 45 tons in weight. Some were carnivorous (meat-
eaters) but the majority were herbivorous (plant-eaters). Some were bipedal (walked on their hind-legs) while
others were quadrupedal (walked on all fours), and although most of the dinosaurs were terrestrial in habitat,
aquatic and semi-aquatic forms were also present.

According to the structure of their hip bones, the dinosaurs have been divided into two great orders. These are the
Saurischia (forms with lizard-like pelvic girdle) and the Ornithischia (dinosaurs with a bird-like pelvic girdle).

96
Plate 43
Dr. Brown, R. T. Bird, and Dr. Schaikjer with the skull of Phobosuchus, an extinct crocodile from the Cretaceous of Trans-Pecos
Texas.
Photograph courtesy of the American Museum of Natural History.

Order Saurischia.— 97
Dinosaurs belonging to this order were particularly abundant during the Jurassic and are characterized by hip
bones that are similar to those of modern lizards. These dinosaurs were first discovered in rocks of Triassic age and
did not become extinct until the end of the Cretaceous. The lizard-hipped reptiles are divided into two rather
specialized groups of dinosaurs: the theropods (carnivorous bipedal dinosaurs that varied greatly in size) and the
sauropods (herbivorous, quadrupedal, semi-aquatic, usually gigantic dinosaurs).
SUBORDER THEROPODA.—
This type of saurischian dinosaur walked on bird-like hind limbs, and they were exclusively meat-eating forms,
such as Allosaurus (Pl. 44) of Jurassic age. Some theropods were exceptionally large and were undoubtedly
vicious beasts of prey. This assumption is borne out by such anatomical features as the small front limbs with long
sharp claws for holding and tearing flesh, and the large strong jaws which were armed with numerous, sharp,
dagger-like teeth. The largest of all known theropods was Tyrannosaurus rex which, when standing on his hind
limbs, was almost 20 feet tall. Some individuals were as much as 50 feet long, and Tyrannosaurus is believed to
have been among the most vicious animals to ever inhabit our earth. A cast of the skull of one of these great beasts
is on display in the Texas Memorial Museum at Austin, and a Tyrannosaurus tooth has been found in the Big Bend
National Park in Trans-Pecos Texas.
SUBORDER SAUROPODA.—
The sauropods were the largest of all dinosaurs, and some attained a length of 85 feet and probably weighed 40 to
50 tons (Brontosaurus, Pl. 44). They were primarily herbivorous dinosaurs which had become adapted to an
aquatic or semi-aquatic type of existence and probably inhabited lakes, rivers, and swamps. The tracks of sauropod
dinosaurs have been collected from Lower Cretaceous rocks in central Texas (Pl. 4) and Upper Cretaceous beds in
Big Bend National Park in Trans-Pecos Texas.

Order Ornithischia.—
The ornithischian, or bird-hipped dinosaurs, were herbivorous reptiles which were quite varied in form and size
and appear to have been more highly developed than the saurischians. This order includes the duck-billed

dinosaurs (ornithopods), the plate-bearing dinosaurs (stegosaurs), the armored dinosaurs (ankylosaurs), and the
horned dinosaurs (ceratopsians). Ornithischian tracks are known from Cretaceous rocks in central and Trans-Pecos
Texas.
SUBORDER ORNITHOPODA.—
These unusual dinosaurs were predominantly bipedal, semi-aquatic, and some (like the duck-billed dinosaurs)
were highly specialized (Trachodon, Pl. 45).
SUBORDER STEGOSAURIA.—
The stegosaurs were herbivorous, quadrupedal ornithischians with large projecting plates down the back and heavy
spikes on their tails. The Jurassic dinosaur Stegosaurus (Pl. 45) is most typical of the plate-bearing forms. This
creature weighed about 10 tons, was some 30 feet long, and stood about 10 feet tall at the hips. Stegosaurus is
characterized by a double row of large, heavy, pointed plates which run along the animal’s back. These plates
begin at the back of the skull and stop near the end of the tail. The tail was also equipped with four or more long
curved spikes which were probably used as a means of defense. The animal had a very small skull which housed a
brain that was about the size of a walnut, and it is assumed that these, and all other dinosaurs, were of very limited
intelligence.

Stegosaurus remains have not been discovered in Texas, but these, like certain other of the extinct vertebrates, are
mentioned because of their interesting and unusual form.
SUBORDER ANKYLOSAURIA.—
The ankylosaurs were four-footed, herbivorous, Cretaceous dinosaurs which had relatively flat bodies. The skull
and back of the animal were protected by bony armor, and the club-like tail was armed with spikes. Paleoscincus
(Pl. 45), a typical ankylosaur, had large spines projecting from along the sides of the body and tail. The armored
spiked back and the heavy club-like tail probably provided Paleoscincus with much-needed protection from the
vicious meat-eating dinosaurs of Cretaceous time.

98
Plate 44
SAURISCHIAN DINOSAURS

ALLOSAURUS × ¹/₁₈₀
BRONTOSAURUS × ¹/₂₅₀

99
Plate 45
ORNITHISCHIAN DINOSAURS

STEGOSAURUS × ¹/₉₀
TRACHODON × ¹/₁₀₀
PALEOSCINCUS × ¹/₂₅
TRICERATOPS × ¹/₁₂₀
SUBORDER CERATOPSIA.—
100
The ceratopsians, or horned dinosaurs, are another group of dinosaurs that are known only from rocks of
Cretaceous age. These plant-eating dinosaurs possessed beak-like jaws, a bony neck frill which extended back
from the skull, and one or more horns. Triceratops (Pl. 45) is the largest of the horned dinosaurs (some forms were
as much as 30 feet long), and the skull measured 8 feet from the tip of the parrot-like beak to the back of the neck
shield.

CLASS AVES.—
Because of the fragile nature of their bodies, birds are seldom found as fossils. In spite of this, however, some
interesting and important fossil bird remains have been discovered.

The oldest known bird was found in Upper Jurassic rocks exposed in Germany. This primitive bird, named
Archaeopteryx, is little more than a reptile with feathers. Archaeopteryx was a pigeon-sized creature which had

scales as well as feathers, a lizard-like tail, a toothed beak, and other definitely reptilian characteristics.

During late Cretaceous time the birds underwent changes that resulted in forms similar to those that are living
today, and most of the present-day birds had developed by the end of the Tertiary.

Although not commonly found, fossil birds have been recorded from certain of the Cenozoic rocks of Texas.

CLASS MAMMALIA.—
The mammals are animals that are born alive and fed with milk from the mother’s breast. They are warm-blooded,
air-breathing, have a protective covering of hair, and are the most advanced of all vertebrates. The foregoing
features are the more typical mammalian characteristics, but exceptions to these are found in certain mammals.

Mammals first appeared in the Jurassic and were probably derived from some form of mammal-like reptile.
Although rare during the Mesozoic, mammals underwent rapid development and expansion during the Cenozoic,
and during this era certain types of mammals became extremely large and assumed many bizarre shapes. The
majority of these unusual forms lived but a short time but are well known from their fossils, and the remains of
some of these animals which inhabited Texas during the Cenozoic may be seen in the Texas Memorial Museum at
Austin.

Recent mammalian classification recognizes several subclasses and numerous orders and suborders, but the
treatment of the mammals in a publication of this nature must of necessity be somewhat brief and no attempt at
detailed classification is made.

Subclass Allotheria.—
The allotherians first appeared during the Jurassic and underwent considerable development in the late Cretaceous
and early Tertiary. Included in this subclass are the multituberculates which are a group of small rodent-like
animals that were probably the earliest of the herbivorous mammals. These animals were probably never very
numerous, and they became extinct during the early part of Eocene time.

Subclass Theria.—
Members of this subclass are first known from rocks of Jurassic age, and they constitute the largest group of
mammals that are living today. Therians undergo considerable development before they are born and at birth
typically resemble the fully developed animal. This subclass has been divided into several orders but only the more
important ones are discussed here.

Order Edentata.—
The edentates are a rather primitive group of mammals which are represented by such living forms as the anteaters,
tree sloths, and armadillos. Members of this group were common in the southern part of the United States in
Pleistocene and Pliocene time, and fossil edentates have been reported from rocks of this age in Texas. One such
form was Mylodon (Pl. 46), one of the extinct giant ground sloths. These huge sloths were quite heavy and some of
them stood as much as 15 feet tall; these great creatures were the forerunners of the modern tree sloths of South
America. The mounted skeleton of one of these giant ground sloths is displayed in the Texas Memorial Museum.

101
Plate 46
CENOZOIC MAMMALS

ENTELODONT × ¹/₃₅
GLYPTODON × ¹/₅₀
MYLODON × ¹/₉₀

Another interesting representative of this order was the glyptodont. These peculiar mammals, which were 102
ancestral to the present-day armadillos, developed at about the same time as the ground sloths. Glyptodon
(Pl. 46), a typical glyptodont that has been reported from the Pleistocene of Texas, is quite characteristic of this
group. This armadillo-like beast had a solid turtle-like shell that in some forms was as much as 4 feet high. From
the front of the bone capped head to the tip of its tail, a large individual might be as much as 15 feet long. The
thick heavy tail was protected by a series of bony rings, and in some species the end of the tail was developed into
a bony heavily spiked club. The carapace (hard outer shell) of a large glyptodont is mounted at the Texas
Memorial Museum.

Order Carnivora.—
Animals belonging to this order are called carnivores and are characterized by clawed feet and by teeth which are
adapted for tearing and cutting flesh. The carnivores, or meat-eaters, were first represented by an ancient group of
animals called creodonts, and this short-lived group first appeared in the Paleocene and were extinct by the end of
the Eocene. They ranged from the size of a weazel to that of a large bear, and their claws were sharp and well

developed. Their teeth, however, were not as specialized as those of modern carnivores, and the creodont brain was
relatively small. It is assumed that these animals had a very low order of intelligence when compared to the more
advanced carnivores of today.

These early meat-eaters were followed by more specialized carnivores which developed throughout Cenozoic
time. Some examples of these are the saber-tooth cat Dinobastis (Pl. 47) and the dire wolf Canis diris (Pl. 47),
both of which have been reported from the Texas Pleistocene. Some remains of these unusual forms, representing
the cat and dog families, are on display at the Texas Memorial Museum.

Order Pantodonta.—
Pantodonts, known also as amblypods, were primitive, hoofed, herbivorous animals. They were distinguished by a
heavy skeleton, short stout limbs, and blunt spreading feet. The pantodonts appeared first during Paleocene time
and had become extinct by the end of the Oligocene.

Order Dinocerata.—
The members of this order are an extinct group of gigantic mammals commonly called uintatheres. Uintatherium
(Pl. 48), which is typical of the group, had three pairs of blunt horns, and the males had dagger-like upper tusks.
Some of the uintatheres were as large as a small elephant and stood as much as 7 feet tall at the shoulders. The size
of the brain in relation to the size of the body suggests that these animals were not as intelligent as most mammals.
Uintatheres are known from rocks ranging from Paleocene to Eocene in age. Uintathere remains have been
reported from Big Bend National Park in Trans-Pecos Texas.

Order Proboscidea.—
The earliest proboscideans, the elephants and their relatives, first appeared in the late Eocene of Africa and were
about the size of a small modern elephant but had larger heads and shorter trunks. Proboscidean development is
marked by an increase in size, change in skull and tooth structure, and elongation of the trunk. Two well-known
fossil proboscideans are the mammoth and the mastodon, both of which inhabited Texas during Pleistocene time.
The mastodons resembled the elephants, but the structure of their teeth was quite different (fig. 25). Moreover, the
mastodon skull was lower than that of the elephant and the tusks were exceptionally large—some reaching a length
of 9 feet.

103
Plate 47
CENOZOIC MAMMALS

DINOBASTIS × ¹/₂₀
CANIS DIRUS × ¹/₁₅
HYRACOTHERIUM × ¹/₁₀
PLIOHIPPUS × ¹/₂₀

There were several types of mammoths, and the woolly mammoth is probably the best known. This animal 104
lived until the end of the Pleistocene and, like the woolly rhinoceros discussed below, is known from ancient
cave paintings and frozen remains. Information gathered from these sources indicates that this great beast had a
long coat of black hair with a woolly undercoat (Pl. 49).

Fig. 25. Sketches of Pleistocene (a) mastodon tooth (×⅙) and (b) mammoth tooth (×⅙).

During the Pleistocene, mammoths were widespread over the United States, and their remains are abundant in
many stream deposits of this age. Proboscidean bones have been reported from Pleistocene rocks in many parts of
Texas, where they are commonly found in sand and gravel pits.

Order Perissodactyla.—
The perissodactyls, or odd-toed animals, are mammals in which the central toe on each limb is greatly enlarged.
Modern representatives include the horses, rhinoceroses, and tapirs. Extinct members of the Perissodactyla include
the titanotheres, chalicotheres, and baluchitheres, all of which grew to tremendous size and took on many unusual
body forms.
HORSES.—
One of the first perissodactyls was Hyracotherium (also called Eohippus), which is the earliest known horse (Pl.
47). This small animal, whose remains have been found in Big Bend National Park, was about 1 foot high and his
teeth indicate a diet of soft food. Following the first horse, there is a long series of fossil horses which provide
much valuable information on the history of this important group of animals.

The record of the development of the horse is well represented in Texas, and the bones and teeth of fossil horses
are common in certain parts of the State. Fossils of this type have been reported from the Tertiary of the Trans-
Pecos, Gulf Coastal Plain, and High Plains regions of Texas, and the teeth of Pleistocene horses have been found in
sand and gravel pits in many parts of the State. Horse teeth (fig. 26) are particularly useful fossils as they may be
accurately identified and used to determine the age of the rocks in which they are found.

Fig. 26. Typical Pliocene horse tooth. Top view (a) and lateral view (b) of molar tooth (×½).

TITANOTHERES.—
This group of odd-toed mammals appeared first in the Eocene, at which time they were about the size of a sheep.
By Middle Oligocene time they had increased to gigantic proportions but still had a small and primitive brain.
Brontotherium (Pl. 48) was slightly rhinoceros-like in appearance and is believed to be the largest land animal that
ever inhabited the North American continent. This animal was about 8 feet tall at the shoulders; a large bony
growth protruded from the skull and this was extended into a flattened horn, which was divided at the top.

105
Plate 48
TERTIARY MAMMALS

UINTATHERIUM × ¹/₄₅
BRONTOTHERIUM × ¹/₃₅

Although the titanotheres underwent rapid development during the early Tertiary, these huge beasts became 106
extinct during the middle of the Oligocene epoch. Titanothere remains have been reported from the Trans-
Pecos region of Texas.
CHALICOTHERES.—
The chalicotheres were in some ways like the titanotheres, but they also exhibited many peculiarities of their own.
The head and neck of Moropus, a typical chalicothere, were much like that of a horse, but the front legs were
longer than the hind legs, and the feet resembled those of a rhinoceros except that they bore long claws instead of
hoofs. The chalicotheres lived in North America from Miocene until Pleistocene time but were probably never
very numerous, and their remains have not yet been discovered in Texas.
RHINOCEROSES.—
The rhinoceroses are also odd-toed animals, and there are many interesting and well-known fossils in this group.
The woolly rhinoceros (Pl. 49) was a Pleistocene two-horned form that ranged from southern France to
northeastern Siberia. The woolly rhinoceros is well known from complete carcasses recovered from the frozen
tundra of Siberia and from remains that were found preserved in an oil seep in Poland. These unusual specimens

plus cave paintings made by early man have given a complete and accurate record of this creature. Although the
woolly rhinoceros has not been reported from Texas, other fossil rhinoceroses have been found in the High Plains
and Gulf Coastal Plain of Texas. These fossils have been found in rocks ranging from Middle Oligocene to late
Pliocene in age.

Baluchitherium, the largest land mammal known to science, was a hornless rhinoceros that lived in late Oligocene
and early Miocene time. This immense creature measured approximately 25 feet from head to tail, stood almost 18
feet high at the shoulder, and must have weighed many tons. Remains of these creatures have not been discovered
in North America, and they appear to have been restricted to Central Asia.

Order Artiodactyla.—
The artiodactyls are the even-toed hoofed mammals and include such familiar forms as pigs, camels, deer, goats,
sheep, and hippopotamuses. This is a large and varied group of animals, but the basic anatomical structure of the
limbs and teeth show well the relationship between the different forms. Artiodactyls are abundant fossils in rocks
ranging from Eocene to Pleistocene in age and are common in rocks of this age in Texas.
ENTELODONTS.—
These giant pig-like artiodactyls lived during Oligocene and early Miocene time and were distinguished by a long
heavy skull that held a relatively small brain. The face was marked by large knobs which were located beneath the
eyes and on the underside of the lower jaw, and although these knob-like structures were blunt they had the
appearance of short horns. Certain of these giant swine attained a height of 6 feet at the shoulders and had skulls
that measured 3 feet in length (Pl. 46). Entelodont remains have been found in the Miocene of the Texas Coastal
Plain.
CAMELS.—
The first known camels have been reported from rocks of upper Eocene age, and these small forms underwent
considerable specialization of teeth and limbs as they developed in size. Many of the camels that lived during the
middle Cenozoic had long legs which were well adapted to running and long necks which would have allowed the
animals to browse on the leaves of tall trees.

The earliest known Texas camels were found in rocks of Oligocene age, and camels, like horses, must have been
abundant in Texas during the Pleistocene for their fossilized remains are common in many parts of the State.

107
Plate 49
CENOZOIC MAMMALS

WOOLLY RHINOCEROS × ¹/₂₀
WOOLLY MAMMOTH × ¹/₄₀

108

BOOKS ABOUT FOSSILS

The following books are recommended for the reader who wants to know more about fossils and fossil collecting.
The publications listed below cover various phases of historical geology and paleontology and range from
children’s books to the more technical publications of the professional paleontologist. This list, however, is by no
means all-inclusive and many other interesting and useful publications are available.

GENERAL WORKS

Dunbar, C. O. (1959) Historical geology, John Wiley and Sons, New York.

College-level text, well written and well illustrated.

Moore, R. C. (1958) Introduction to historical geology, McGraw-Hill Book Co., New York.

College-level presentation of earth history. Many illustrations of fossils.

Moore, Ruth (1953) Man, time, and fossils, Alfred Knopf, New York.

A readable account of fossils and their development throughout geologic time.

Panghorn, M. W., Jr. (1957) Earth for the layman, American Geological Institute, Washington, D. C.

Contains many valuable references.

Raymond, P. E. (1950) Prehistoric life, Harvard University Press, Cambridge, Mass.

College-level text.

Richards, H. G. (1953) Record of the rocks, Ronald Press, New York.

College-level earth history text.

Simpson, G. G. (1953) Life of the past, Yale University Press, New Haven, Conn.

Thorough, yet readable, introduction to paleontology.

Stirton, R. A. (1959) Time, life, and man: the fossil record, John Wiley and Sons, New York.

An introductory college text, most of which is of interest to adult level general readers.

Note: See also sections on Paleontology and Fossils in Encyclopedia Americana, Encyclopaedia Britannica, and
others.

NONTECHNICAL AND JUVENILE

Andrews, R. C. (1953) All about dinosaurs, Random House, New York.

Interesting and readable dinosaur book for junior high and high-school age.

Andrews, R. C. (1956) All about strange beasts of the past, Random House, New York.

Interesting and easy to read, this book deals largely with extinct and unusual mammals (junior high and high
school).

Colbert, E. H. (1945) The dinosaur book, American Museum of Natural History, New York.

A classic among “popular” dinosaur books. For all age levels.

Colbert, E. H. (1957) Dinosaurs, American Museum of Natural History, New York.

This little booklet provides a well-illustrated introduction to the dinosaurs. For high school and adult-level
readers.

Dickinson, Alice (1954) First book of prehistoric animals, Franklin Watts, Inc., New York.

Easy to read, well-illustrated book for grade-school age.

Dunkle, D. H. (1957) The world of the dinosaurs, Smithsonian Institution, Washington, D. C.

An easy to understand, amply illustrated introduction to the dinosaurs (high school-adult level).

Fenton, C. L. (1937) Life long ago, The John Day Co., New York.

Very good for advanced grade and high-school age.

Heal, Edith (1930) How the world began, Thomas S. Rockwell Co., Chicago.

An account of the beginnings of life. For upper grade through high-school age.

Markman, H. C. (1954) Fossils, Denver Museum of Natural History, Denver, Colo.

A well-illustrated general survey of fossils. For adult-level readers.

Matthews III, W. H. (1962) Fossils: An introduction to prehistoric life, Barnes and Noble, Inc., New York, [“In
preparation” at time of first printing of Guidebook No. 2.]

This publication contains many collecting aids and much background material for amateur collectors. Contains
also a brief review of earth history.

Matthews III, W. H. (1963) Wonders of the dinosaur world, Dodd, Mead & Co., New York.

Well illustrated, non-technical presentation of dinosaurs. For junior-high and high-school teachers.

Parker, B. M. (1942) Stories read from the rocks, Basic Science Education Series, Row, Peterson and Co.,
Evanston, Ill.

Well written and colorfully illustrated. For advanced grades and junior high.

Parker, B. M. (1948) Animals of yesterday, Basic Science Education Series, Row, Peterson, and Co., Evanston,
Ill.

Well written and colorfully illustrated. For advanced grades and junior high.

Shaver, R. H. (1959) Adventures with fossils, Geological Survey, Indiana Department of Conservation,
Bloomington, Ind.

Collection hints and general information on fossils. Particularly for the lower grades.

Shuttlesworth, D. E. (1957) Real book of prehistoric life, Garden City Books, Garden City, N. Y.

Survey of prehistoric life. For grade and junior-high levels.

COLLECTING HELPS

Brown, Vinson (1954) How to make a home nature museum, Little, Brown and Co., Boston.

Contains suggestions for collecting, mounting, and displaying fossils and other objects of nature.

Camp, C. L., and Hanna, G. D. (1937) Methods in paleontology, 109
University of California Press, Berkeley.

Excellent discussion of collecting and preparation techniques.

Casanova, Richard (1957) An illustrated guide to fossil collecting,
Natureograph Co., San Martin, Calif.

Has collecting hints and fossil localities for most of the States.

Collinson, C. C. (1959) Guide for beginning fossil hunters, Educational
Series 4, Illinois State Geological Survey, Urbana.

Clearly written, well illustrated, particularly for the lower grades.

Goldring, Winifred (1950) Handbook of paleontology for beginners and
amateurs, New York State Museum, Albany, N. Y.

A complete summary of paleontology. For the advanced collector.

La Rocque, A., and Marple, M. F. (1955) Ohio fossils, Ohio Division of
Geological Survey, Bulletin 54, Columbus, Ohio.

Rather comprehensive treatment of the invertebrates with several useful
keys for fossil identification.

Livingston, V. E., Jr. (1959) Fossils in Washington, Division of Mines and
Geology, Department of Conservation, Olympia, Wash.

An introduction to the geology and fossils of Washington. Contains guide
to collecting localities.

Simpson, B. W. (1958) Gem trails of Texas, Bessie W. Simpson, Granbury,
Texas.

Field guide to Texas mineral, rock, and fossil locations. Contains
numerous maps and well-described collecting localities.

Unklesbay, A. G. (1955) Common fossils of Missouri, University of
Missouri Bulletin, Handbook 4, Columbia, Mo.

Written for the amateur; contains much general information of interest to
the beginning collector.

REFERENCE WORKS

Arnold, C. A. (1947) An introduction to paleobotany, McGraw-Hill Book
Co., New York.

College-level textbook.

Beerbower, J. R. (1960) Search for the past, Prentice-Hall, Inc., Englewood
Cliffs, N. J.

Good background text. Well illustrated. Has section on vertebrates.

Colbert, E. H. (1955) Evolution of the vertebrates, John Wiley and Sons,
New York.

Comprehensive and technical treatment of vertebrate fossils.

Cushman, J. A. (1948) Foraminifera, their classification and economic use,
Harvard University Press, Cambridge, Mass.

College-level text containing large numbers of descriptions and
illustrations of foraminifera.

Easton, W. H. (1960) Invertebrate paleontology, Harper & Bros., Inc., New
York.

College-level text. Good illustrations, useful for identification.

Fenton, C. L., and Fenton, M. A. (1958) The fossil book, Doubleday and
Co., New York.

Comprehensive, easy-to-read, beautifully illustrated treatment of all types
of fossils.

Jones, D. J. (1956) Introduction to microfossils, Harper and Brothers, New
York.

College-level textbook with considerable information on collection,
preparation, and the types of microfossils.

Moore, R. C., et al. (1953-1959) Treatise on invertebrate paleontology,
Geological Society of America and University of Kansas, Lawrence,
Kansas.

A technical reference for the more advanced collector. It is issued in
several parts and contains latest classification.

Moore, R. C., Lalicker, C. G., and Fisher, A. G. (1953) Invertebrate
fossils, McGraw-Hill Book Co., New York.

College-level reference with fine illustrations. Of value for purposes of
identification.

Romer, A. S. (1945) Vertebrate paleontology, University of Chicago Press,
Chicago.

A college-level textbook with numerous illustrations.

Shimer, H. W. (1933) Introduction to the study of fossils, The Macmillan
Company, New York.

A relatively simple college-level presentation of plant and animal fossils.

Shimer, H. W., and Shrock, R. R. (1944) Index fossils of North America,
John Wiley and Sons, New York.

Comprehensive survey of the more common fossils of North America.
Useful to the advanced collector and a most useful aid for fossil
identification.

Shrock, R. R., and Twenhofel, W. H. (1953) Principles of invertebrate
paleontology, McGraw-Hill Book Co., New York.

Useful college-level reference for advanced collectors.

[2]
SELECTED REFERENCES ON TEXAS FOSSILS

*Adkins, W. S. (1920) The Weno and Pawpaw formations of the Texas
Comanchean: Univ. Texas Bull. 1856.

Descriptions and illustrations of many common Cretaceous fossils.

*Adkins, W. S. (1928) Handbook of Texas Cretaceous fossils: Univ. Texas
Bull. 2838.

Lists all fossils described from the Texas Cretaceous prior to 1928, with
many useful illustrations.

*Adkins, W. S., and Winton, W. M. (1919) Paleontological correlation of
the Fredericksburg and Washita formations of north-central Texas: Univ.
Texas Bull. 1945.

Contains descriptions and illustrations of many common Lower
Cretaceous fossils of north-central Texas.

Clarke, W. B., and Twitchell, M. W. (1915) The Mesozoic and Cenozoic
Echinodermata of the United States: U. S. Geological Survey Monograph
54, Washington, D. C.

A valuable guide to the Mesozoic and Cenozoic echinoderms of Texas.

*Frizzell, D. L. (1954) Handbook of Cretaceous Foraminifera of 110
Texas: Univ. Texas, Bureau Econ. Geol. Rept. Inves. No. 22.

A technical, but invaluable aid in the study of Texas Cretaceous
microfossils.

*Girard, R. M. (1959) Bibliography and index of Texas geology, 1933-
1950: Univ. Texas Pub. 5910.

This valuable reference guide contains many references to Texas fossils.
Note especially entries under Paleontology in the index.

Heuer, Edward (1958) Comments on the nomenclature revision of the
Strawn and Canyon megafossil plates, in A guide to the Strawn and
Canyon Series of the Pennsylvanian System in Palo Pinto County, Texas,
An Occasional Publication of the North Texas Geological Society,
Wichita Falls, Texas.

Contains illustrations and latest name changes of many of the more
common Pennsylvanian fossils of north Texas.

*King, R. E. (1930) Geology of the Glass Mountains, Part II, Faunal
summary and correlation of the Permian formations with description of
Brachiopoda: Univ. Texas Bull. 3042.

Contains descriptions and illustrations of numerous brachiopods from the
Glass Mountains of Trans-Pecos Texas.

*Lee, Wallace, et al. (1939) Stratigraphic and paleontologic studies of the
Pennsylvanian and Permian rocks of north-central Texas: Univ. Texas
Pub. 3801.

Contains an extensive faunal list and important collecting localities for
Pennsylvanian invertebrates.

*Moore, R. C., and Jeffords, R. M. (1944) Description of lower
Pennsylvanian corals from Texas and adjacent states: Univ. Texas Pub.
4401, pp. 77-208.

Describes and illustrates many of the more common Pennsylvanian
corals.

*Plummer, F. B. (1943) The Carboniferous rocks of the Llano region of
central Texas: Univ. Texas Pub. 4329.

Contains geologic map, locality data, and illustrations of many
Carboniferous fossils.

*Plummer, F. B., and Moore, R. C. (1921) Stratigraphy of the
Pennsylvanian formations of north-central Texas: Univ. Texas Bull. 2132.

Describes and illustrates many of the more common Pennsylvanian
fossils of north-central Texas.

*Plummer, F. B., and Scott, Gayle (1937) Upper Paleozoic ammonites in
Texas: Univ. Texas Bull. 3701, pt. 1.

*Renick, B. C., and Stenzel, H. B. (1931) The lower Claiborne of the
Brazos River, Texas: Univ. Texas Bull. 3101, pp. 73-108.

Contains discussion and illustrations of many common Tertiary fossils.

Sellards, E. H. (1955) Texas through 250 million years: Museum Notes
No. 4, Texas Memorial Museum, Austin.

This little booklet provides a short geologic history of Texas along with a
review of oil in Texas.

*Sellards, E. H., Adkins, W. S., and Plummer, F. B. (1933) The geology
of Texas, Vol. I, Stratigraphy: Univ. Texas Bull. 3232 (August 22, 1932).

This important publication will give the advanced collector much valuable
information on the distribution of the rocks of Texas. Complete with
geologic map.

Stanton, T. W. (1947) Studies of some Comanche pelecypods and
gastropods: U. S. Geological Survey Prof. Paper 211, Washington, D. C.

Describes and illustrates most of the more common Lower Cretaceous
pelecypods and gastropods of the State.

*Stenzel, H. B., Krause, E. K., and Twining, J. T. (1957) Pelecypoda
from the type locality of the Stone City beds (Eocene) of Texas: Univ.
Texas Pub. 5704.

Descriptions and illustrations of many of the more common Tertiary clams
and oysters.

*Stephenson, L. W. (1941) The larger invertebrate fossils of the Navarro
group of Texas: Univ. Texas Pub. 4101.

Contains descriptions of many common Upper Cretaceous invertebrates
(exclusive of corals and crustaceans).

Stephenson, L. W. (1952) Larger invertebrate fossils of the Woodbine
formation (Cenomanian) of Texas: U. S. Geological Survey Prof. Paper
242, Washington, D. C.

*Winton, W. M. (1925) The geology of Denton County: Univ. Texas Bull.
2544.

Illustrates and discusses the occurrence of many Cretaceous fossils.

*Winton, W. M., and Adkins, W. S. (1920) The geology of Tarrant County:
Univ. Texas Bull. 1931.

Contains many illustrations of common north Texas Cretaceous fossils.

111

GLOSSARY

Amber—a hard, yellowish, translucent, fossilized plant resin.

Ammonite—ammonoid cephalopod with complexly wrinkled suture
pattern; member of subclass Ammonoidea.

Anterior—front or fore.

Anus—the terminal opening of the alimentary canal, through which waste
matter is discarded from the body.

Aperture—the opening of shells, cells, etc.

Aragonite—calcium carbonate (CaCO₃) crystallizing in a different form
than calcite. In shells it is chalky and opaque; is less stable than calcite.

Archeozoic—the oldest known geological era; early Precambrian time.

Articulated—joined by interlocking processes or by teeth and sockets.

Asymmetrical—without or lacking symmetry.

Bilateral—pertaining to the two halves of a body as symmetrical and
mirror images of each other.

Binomial nomenclature—system of scientific nomenclature requiring two
names: generic and trivial.

Blastoid—stalked echinoderm with bud-like calyx usually consisting of 13
plates; member of class Blastoidea.

Brachiopod—bivalved marine invertebrate; member of phylum
Brachiopoda.

Brackish—a mixture of salt and fresh waters.

Burrow—a hole in the ground, rock, wood, etc., made by certain animals
for shelter or while gathering food.

Calcareous—composed of, or containing, calcium carbonate; limy.

Calcite—calcium carbonate (CaCO₃) crystallizing in a different form than
aragonite. In shells it is translucent and more stable than aragonite.

Cambrian—the first (oldest) period of the Paleozoic era.

Calyx—in corals the bowl-shaped depression in the upper part of the
skeleton; in stalked echinoderms that part of the body which contains
most of the soft parts.

Caprinid—a Cretaceous pelecypod that is typically coiled in the form of a
ram’s horn.

Carapace—the hard protective covering that forms the exoskeleton of
many invertebrates; in arthropods it is usually chitinous or calcaro-
chitinous.

Carbonization—the process of fossilization whereby organic remains are
reduced to carbon or coal.

Cast—the impression taken from a mold.

Cenozoic—the latest era of geologic time, following the Mesozoic era and
extending to the present.

Cephalon—the head; in trilobites the anterior body segment forming the
head.

Cephalopod—marine invertebrate with well-defined head and eyes and
with tentacles around the mouth; member of class Cephalopoda,
phylum Mollusca; includes squids, octopuses, pearly nautilus.

Ceratite—an ammonoid cephalopod with suture composed of rounded
saddles and jagged lobes; member of subclass Ammonoidea.

Chert—a cryptocrystalline variety of silica; flint is a variety of chert.

Chitin—a horn-like substance, found in the hard parts of many animals,
such as beetles, crabs, etc.

Chitinous—composed of chitin.

Cirri—in crinoids, the jointed appendages which branch off the side of the
stem or from the base of some crinoid stems.

Coelenterate—invertebrates characterized by a hollow body cavity, radial
symmetry, and stinging cells; a member of phylum Coelenterata;
includes jellyfishes, corals, sea anemones.

Colonial—in biology refers to the way in which some invertebrates live in
close association with, and are more or less interdependent upon, each
other; colonial corals, hydroids, etc.

Columella—a small column or central axis; in corals the small rod or axial
pillar in the center of the corallite; in gastropods the solid or perforate
pillar formed by the union of the successive coils of a conispiral shell.

Columnal—one of the disk-shaped segments of a crinoid stalk.

Concentric—having a common center, as circles; refers to shell markings
that are parallel to shell margin.

Concretion—nodular or irregular masses in sedimentary rocks and usually
formed around a central core, which is often a fossil.

Conical—cone-shaped.

Conodont—minute tooth-like fossils found in certain Paleozoic rocks; their
origin is not definitely known, but they may have been part of some
type of extinct fish.

Coral—bottom-dwelling marine invertebrate that secretes calcareous hard
parts; member of class Anthozoa, phylum Coelenterata.

Corallite—the skeleton formed by an individual coral animal; may be
solitary or form part of a colony.

Corallum—the skeleton of a coral colony.

Corona—crown; in echinoids the main part of the skeleton consisting of
symmetrically arranged calcareous plates.

Coprolite—the fossil excrement of animals.

Correlation—the process of demonstrating that certain strata are closely
related to each other or that they are stratigraphic equivalents.

Cretaceous—the third and last period of the Mesozoic era.

Cystoid—an extinct stemmed echinoderm with calyx composed of
numerous irregularly arranged plates; member of class Cystoidea.

Dendritic—resembling a tree, branching.

Dentition—the system or arrangement of teeth peculiar to any given
animal.

Devonian—the fourth oldest period of the Paleozoic era, follows the
Silurian, precedes the Mississippian.

Dip—the angle of inclination which the bedding plane of rocks makes with
a real or imaginary horizontal line.

Distillation—in fossils that process by which volatile organic matter is
removed, leaving a carbon residue.

Dolomite—a mineral composed of calcium magnesium carbonate
(CaMg(CO₃)₂).

Dorsal—pertaining to the back. 112

Echinoderm—a marine invertebrate with calcareous exoskeleton and
usually exhibiting a five-fold radial symmetry; member of phylum
Echinodermata; includes cystoids, blastoids, crinoids, starfishes, and
sea urchins.

Echinoid—bottom-dwelling, unattached marine invertebrate with
exoskeleton of calcareous plates covered by movable spines; member
of class Echinoidea; sea urchins, heart urchins, biscuit urchins.

Endoskeleton—the internal supporting structure of an animal.

Eocene—the next to earliest of the Tertiary epochs, follows the Paleocene
and precedes the Oligocene.

Equivalved—right and left valves subequal and (except for hinge
structures) comprising mirror images of each other.

Evolution—a term applied to those methods or processes and to the sum of
those processes whereby organisms change through successive
generations.

Exoskeleton—an external skeleton, or hard covering for the protection of
soft parts, particularly among invertebrates.

Fault—the displacement of rocks along a zone of fracture.

Fauna—an assemblage of animals (living or fossil) living in a given place
at a given time.

Flank—the side or lateral portion of anything.

Flora—an assemblage of plants (living or fossil) living in a given place at a
given time.

Fold—in brachiopods, a major rounded elevation of shell which affects
both inner and outer shell surfaces.

Foramen—in brachiopods, the opening in the pedicle valve near the beak
where the pedicle extends through the shell.

Foraminifer—a protozoan usually possessing a calcareous, perforated,
chambered shell, but shell may be chitinous or agglutinated; a member
of the order Foraminifera, phylum Protozoa.

Formation—a rock unit useful for mapping and distinguished primarily on
the basis of lithologic characters.

Fossil—the remains or traces of organisms buried by natural causes and
preserved in the earth’s crust.

Guide fossil—a fossil which, because of its limited vertical but wide
horizontal distribution, is of value as a guide or index to the age
of the rocks in which it is found.

Fossiliferous—containing fossilized organic remains.

Fusulinid—a spindle-shaped foraminifer: test shaped like a grain of wheat.

Gastrolith—highly polished well-rounded pebbles found associated with
certain reptilian fossils; “stomach stones.”

Gastropod—a terrestrial or aquatic invertebrate, typically possessing a
single-valved, calcareous, coiled shell; member of class Gastropoda,
phylum Mollusca: snails and slugs.

Geologic age—the age of an object as stated in terms of geologic time (e.g.,
a Pennsylvanian fern, Cretaceous dinosaur).

Geologic map—map showing distribution of rock outcrops, structural
features, mineral deposits, etc.

Geologic range—the known duration of an organism’s existence
throughout geologic time (e.g., Cambrian to Recent for brachiopods).

Glauconite—a greenish mineral commonly formed in marine environments
and essentially a hydrous silicate of iron and potassium.

Goniatite—an ammonoid cephalopod with suture composed of smooth
saddles and simple angular lobes; member of subclass Ammonoidea.

Graptolite—an extinct, marine, colonial organism with chitinous hard
parts; believed to belong to subphylum Hemichordata of phylum
Chordata.

Guide fossil—see Fossil.

Habitat—the physical environment in which an organism lives.

Hinge-line—in brachiopods, the edge of the shell where the two valves
articulate; in pelecypods, the dorsal margin of the valve which is in
continual contact with the opposite valve.

Igneous rock—rocks which have solidified from lava or molten rock called
magma.

Index fossil—see Fossil.

Inequivalved—opposite valves unlike in shape or size, or both.

Jurassic—second oldest period of the Mesozoic; follows the Triassic,
precedes the Cretaceous.

Keel—a strong continuous ridge along the ventral side of ammonites.

Larva—the young form of some animals before they assume the mature
shape.

Lateral—side or to the side.

Lithology—the study and description of rocks based on the megascopic
(with the naked eye) examination of samples. Used also to refer to the
texture and composition of any given rock sample.

Living chamber—in mollusks, that part of the shell which is occupied by
the living animal.

Lobe—in cephalopods, the backward flexure of the suture or septum.

Longitudinal—in a direction parallel with the length.

Lophophore—in brachiopods, a tentacle-bearing appendage attached to the
anterior surface of the mantle cavity.

Mantle—in mollusks and brachiopods, a layer of tissue containing cells
that secrete the shell.

Meso-—a prefix signifying middle.

Mesozoic—that era of geologic time that precedes the Cenozoic and
follows the Paleozoic.

Miocene—fourth oldest epoch of the Tertiary period; follows the
Oligocene, precedes the Pliocene.

Mississippian—fifth oldest period of the Paleozoic: follows the Devonian,
precedes the Pennsylvanian.

Multicellular—composed of more than one cell.

Nacreous—pearly.

Node—a knob.

-oid—a suffix meaning “in the form of.”

Oligocene—the third oldest epoch of the Tertiary period: precedes the
Miocene, follows the Eocene.

Operculum—the lid or covering of the aperture of certain shells.

Oral—referring to the mouth or aperture.

Orbitoidids—foraminifers with large typically disk-shaped tests.

Ordovician—second oldest period of the Paleozoic era; follows the
Cambrian, precedes the Silurian.

Ossicle—loosely used as a small plate. 113

Paleocene—oldest epoch of the Tertiary period; precedes the Eocene.

Paleozoic—that era of geologic time that follows Precambrian time and
precedes the Mesozoic era.

Pedicle opening (pedicle foramen)—see Foramen.

Pelecypod—a bivalved aquatic invertebrate; member of class Pelecypoda,
phylum Mollusca.

Pennsylvanian—the sixth oldest period of the Paleozoic era; follows the
Mississippian, precedes the Permian.

Period—a division of geologic time (Pl. 1).

Periostracum—the horny outer covering or epidermis on shells.

Permian—seventh and last period of the Paleozoic.

Permineralization—that process by which mineral matter has been added
to the original shell material by precipitation in the interstices rather
than replacing the original shell material.

Phosphatic—containing or pertaining to phosphate minerals.

Phylum—one of the primary divisions of the animal or vegetable
kingdoms.

Planispiral—shell coiled in one plane.

Pleistocene—earliest epoch of Quaternary period, Cenozoic era; follows
Pliocene epoch of Tertiary period, precedes Recent epoch of

Quaternary.

Pleural—referring to the side or ribs; in trilobites, refers to lateral portions
of thorax and pygidium.

Pliocene—latest epoch of Tertiary period of Cenozoic era; follows Miocene
epoch and precedes Pleistocene epoch of Quaternary period.

Polygonal—many sided or having many-sided plates.

Polyp—a many-tentacled aquatic coelenterate animal, typically cylindrical
or cup-shaped, as in corals.

Porcelaneous—like porcelain.

Pore—a very small opening.

Posterior—situated behind; to the rear.

Precambrian—that portion of geologic time before the Cambrian; divided
into Archeozoic era (Early Precambrian) and Proterozoic era (Late
Precambrian).

Protero—combining form meaning fore, former, or anterior in time (Greek
proteros, fore).

Proterozoic—youngest era of the Precambrian; follows the Archeozoic era
and precedes the Cambrian period of the Paleozoic era.

Protista—the organic kingdom including the simplest of all one-celled
organisms which possess various characters of both plants and
animals; bacteria, algae, foraminifers, radiolarians.

Protoconch—in mollusks, the initial chamber of shell.

Pyrite—a hard, brass-yellow mineral composed of iron sulfide; “fool’s
gold.”

Quaternary—the youngest period of the Cenozoic era, follows the Tertiary
period.

Radial symmetry—see Symmetry.

Reef—a mound-like or ridge-like elevation of the sea bottom which almost
reaches the surface of the water, composed primarily of organic
material and commonly formed by reef-building animals, such as
corals and oysters.

Replacement—type of fossilization whereby hard parts of organisms are
removed by solution accompanied by almost simultaneous deposition
of other substances in the resulting voids; mineralization.

Respiration—the process of oxygenation.

Rock—an aggregation of one or more minerals.

Rock-unit—divisions of rocks based on definite physical and lithologic
characteristics and not defined on the basis of geologic time alone;
groups, formations, members.

Rudistid—a Cretaceous pelecypod that does not exhibit the typical clam or
oyster shape; many are cone-shaped, resembling corals.

Saddle—in cephalopods, the forward flexure (curved toward the aperture)
of the suture or septum.

Scaphopod—an exclusively marine mollusk with a single-valved tusk-
shaped shell; member of class Scaphopoda, phylum Mollusca.

Scavenger—an animal that feeds on organic refuse.

Sedentary—stationary in life, not moving from place to place.

Sediment—material that has been deposited by settling from a
transportation agent such as water or air; typically composed of
weathered rock fragments.

Sedimentary rock—rocks formed from the accumulation and lithification
of sediments.

Segment—one of the parts into which a body naturally separates or is
divided; for example, segments of arthropods or annelid worms.

Septal—pertaining to the septum.

Septum (plural, septa)—a dividing wall or partition; in fusulinids, a
partition between chambers in the fusulinid shell; in corals, one of the
radiating, longitudinal, calcareous plates located within the corallite; in
cephalopods, the transverse partitions between the chambers.

Series—the rocks formed during an epoch; the time-stratigraphic term next
in rank below a system.

Serrate—notched like a saw.

Sessile—animal attached to the sea floor more or less permanently.

Silica—an oxide of silicon (SiO₂).

Siliceous—containing or pertaining to silica.

Silicification—the process of combining or impregnating with silica.

Silurian—the third oldest period of the Paleozoic era; follows the
Ordovician, precedes the Devonian.

Sinus—an elongate depression on brachiopod shells.

Siphuncle—in cephalopods, the segmented horny or calcareous tube which
extends from the protoconch to the living chamber.

Slickensides—polished and grooved surfaces that are the result of two rock
masses sliding past each other as in faulting.

Solitary—living alone; not part of a colony.

Species—one of the smaller natural divisions in classification.

Specific name—see Trivial name.

Spicule—a minute spike or dart, skeletal element in sponges and
holothurians.

Stratum (plural, strata)—a single bed or layer of rock.

Strike—the direction of a real or imaginary line that is formed by the
intersection of a bed or stratum with a horizontal plane; strike is
perpendicular to the dip.

Subconical—less than conical in shape; almost a cone. 114

Suture—the line of junction between two parts; in crinoids, the line of
junction between two plates; in gastropods, the line of junction of the
whorls as seen on the exterior of the shell; in cephalopods, the line of
junction between a septum and the shell wall.

Symmetry—orderly arrangement of parts of an object with reference to
lines, planes, or points.

Bilateral symmetry—the symmetrical duplication of parts on each side
of a vertical anterior-posterior plane.

Radial symmetry—the symmetrical repetition of parts around a
common vertical dorso-ventrally disposed axis.

Pentamerous symmetry—symmetry arranged in a pattern of fives.

System—the rocks formed during a period; the time-stratigraphic term next
in rank above a series.

Taxonomy—that branch of science that deals with classification, especially
in relation to plants, animals, or fossils.

Tertiary—the oldest period of the Cenozoic era; follows the Cretaceous
period of the Mesozoic and precedes the Quaternary period of the

Cenozoic.

Test—the protective covering of some invertebrate animals.

Theca—a sheath or case; in coelenterates, the bounding wall at or near the
margin of the exoskeleton; in echinoderms, the main body skeleton (or
calyx) which houses the animal’s soft parts; in graptolites, any cup or
tube of the colony.

Thorax—in trilobites, that part of the body between the cephalon and
pygidium.

Time-unit—a portion of continuous geologic time (e.g., eras, periods,
epochs, and ages).

Time-rock unit—same as time-stratigraphic unit.

Time-stratigraphic unit—term given to rock units with boundaries
established by geologic time; strata deposited during definite portions
of geologic time (e.g., systems, series, stages, etc.).

Topography—the physical features or configuration of a land surface.

Topographic map—a map showing the physical features of an area,
especially the relief and contour of the land.

Transverse—at right angles to length.

Triassic—the youngest period of the Mesozoic era; follows the Permian
period of the Paleozoic and precedes the Jurassic period of the
Mesozoic.

Trilobite—an extinct marine arthropod having a flattened segmented body
covered by a hardened dorsal exoskeleton divided into three lobes.

Trivial name—the Latinized name added to a generic name to distinguish
the species; same as specific name.

Type locality—the geographic location at which a formation was first
described and from which it was named; or from which the type
specimen of a fossil species comes.

Type specimen—the individual or specimen on which the original
designation of a species was established.

Umbilicus—an external depression or opening at the center of many
loosely coiled shells; in gastropods it is usually located at the base of
the shell; in cephalopods it is usually located laterally.

Umbo—the arched part of the valve near the beak in bivalve shells.

Unicellular—composed of one cell.

Valve—the one or more pieces comprising the shell of animals.

Variety—a subdivision of a species, designated by a third name when a
variety is designated.

Ventral—pertaining to the abdomen; as opposed to dorsal, pertaining to the
back.

Vertebrate—an animal having a backbone or spinal column.

Whorl—a single turn or volution of a coiled shell.

-zoic—combining form meaning “life” (Greek zoikos, life).

Zooecium (plural, zooecia)—tube or chamber occupied by an individual of
the bryozoan colony; also called an autopore.

Footnotes

[1]
Associate Professor of Geology, Lamar State College of Technology,
Beaumont, Texas.

[2]
Entries marked with asterisk are published by the Bureau of Economic
Geology, The University of Texas, Austin. Those not out of print are
distributed at nominal sale price; list sent on request. These publications
may be consulted at many public libraries and/or Chamber of
Commerce offices.
115

Index

Page numbers in italics indicate illustrations.

A B C D E F G H I J K L M N O P Q R S T U V
W X Y Z

A
Acanthoceras: 77
Actinomma: 49
Africa: 87
Agnatha: 87
Alaska: 7
Alectryonia lugubris: 68
algae: 44, 46, 47
“algal biscuits”: 44
alligators: 95
Allorisma: 67
Allosaurus: 90, 97, 98
Allotheria: 100
allotherians: 100
Amarillo College: 27
amber: 7
amblypods: 102
Ambocoelia: 57
Amelanchier: 48
American Museum of Natural History: 2, 15, 96
ammonites: 11, 75, 76, 77, 78

Ammonoidea: 66
ammonoids: 75, 76, 77, 78
Amphibia: 89
amphibians: 87, 92
Amphineura: 56
Amphiscapha: 61
Ancilla: 64
Angulotreta: 55, 56
ankylosaurs: 90, 97, 99
Annelida: 78
annelids: 78
Anomia: 74
anteaters: 100
Anthozoa: 49, 51
Apsotreta: 55, 56
aragonite: 11
Archelon: 91
Archetectonica: 64
Archaeopteryx: 100
Archeozoic, derivation and pronunciation: 33
Archer County: 89
Archimedes: 54
arietina, Exogyra: 70
Aristotle: 3
Arizona: 7
Arkansas: 37
Arlington State College: 1, 27
armadillos: 100, 102
Aronow, Saul: 1
Arthropoda: 78, 79, 80
arthropods: 10, 78, 79, 80
crustaceans: 79, 80
insects: 7, 79
ostracodes: 79, 80
trilobites: 78, 80
Articulata: 56
Artiodactyla: 106

artiodactyls: 106
camels: 106
entelodonts: 101, 106
ash, volcanic: 5
Astacodes: 79
Astartella: 67
Asteroidea: 82
asteroids: 82, 83
Asterozoa: 82
Astraeospongium: 50
Astrhelia: 53
Astylospongia: 50
Aulosteges tuberculatus: 12, 13
Austin: 14, 17, 19, 87
Austin College: 27
Australia: 87
author, of a fossil: 22
autopores: 51
Aves: 89, 100
Avonia: 12, 13
signata: 12, 13
subhorrida: 12, 13

B
bacteria: 47
Baculites: 77
bags, collecting: 17, 18
Balcones fault zone: 36, 37
baluchitheres: 104, 106
Baluchitherium: 106
Barbatia: 74
Baylor County: 89
Baylor University: 1, 2, 27, 90, 91, 95
Beaumont: 1, 34
clay: 34
Beaver, Harold: 1
Belemnites: 77, 78

Belemnoidea: 78
belemnoids: 77, 78
Bellerophon: 61
Big Bend area: 35, 36
National Park: 35, 97, 102
Big Spring: 89
binomial nomenclature: 21-22
Bird, R. T.: 2, 15, 96
birds, fossil: 5, 100
Blastoidea: 81
blastoids: 26, 28, 81
Blinn College: 27
bone, permineralized: 9
Books About Fossils: 108-110
Boon, Jack: 1
Brachiopoda: 54, 55, 56
brachiopods: 26, 29, 54, 55, 56
articulate: 54, 55, 56, 57, 58
Cambrian: 55
Cretaceous: 56
inarticulate: 55, 56
Mississippian: 55
Pennsylvanian: 57, 58
Permian: 12, 13
Recent: 56
silicified: 12, 13
symmetry: 24, 26, 29
Brachiosaurus: 90
Brewster County: 11, 12, 35, 41
brittle stars: 82
Bronaugh, Richmond L.: 1
Brontosaurus: 90, 97, 98
Brontotherium: 104, 105, 106
Brown, L. F., Jr.: 1
Bryophyta: 44
Bryozoa: 51, 54, 55
bryozoans: 26, 27, 28, 30, 51, 54, 55, 84 116

Mississippian: 54
Pennsylvanian: 55
bulla, Venericardia: 72
Bureau of Economic Geology: 2, 19
burrows: 14
“button corals”: 49, 53

C
Calamites: 48
calcite: 10, 11
callus: 59
Calyptraphorus: 64
Camarotoechia: 55
Cambrian—
derivation and pronunciation: 34
fossils: 40
brachiopods: 55
graptolites: 86
of Franklin Mountains, Llano, Marathon, and Solitario uplifts: 40
camels: 106
cameratus, Neospirifer: 58
Caninia: 51, 52
Canis diris: 102, 103
domestica: 22
caprinid: 27, 30
caprock, of High Plains: 35
carbon residues: 10, 86
Carboniferous: 34
carinata, Ostrea: 71
Carnivora: 102
carnivores: 102, 103
Caryocorbula: 74
Caryocrinites: 81
Casey, Josephine: 2
casts: 11
catalog, fossil; number: 31
cement, portland: 19

Cenozoic—
derivation and pronunciation: 33
periods of: 34
rocks in Texas: 43
central Asia: 106
central Texas: 11, 42
Cephalopoda: 56, 66, 75, 78
cephalopods: 24, 26, 27, 28, 29, 30, 66, 75, 76, 77, 78
ammonites: 75, 76, 77, 78
ammonoids: 75, 76, 77, 78
belemnoids: 77, 78
ceratites: 75, 78
coleoids: 77, 78
cuttlefish: 78
goniatites: 75, 76
nautiloids: 66, 75, 76
octopus: 66, 78
squid: 66, 78
sutures: 66, 75, 78
ceratites: 75, 78
ceratopsians: 90, 99, 100
Ceratosaurus: 90
Cerithium: 62
chalicotheres: 104, 106
Chelonia. See turtles.
chisels: 17
chitin: 10
chitons: 56
Chondrichthyes: 87
Chonetes: 57
Chordata: 84-102
chordates: 84
amphibians: 89, 92
birds: 100
fishes: 87, 88, 89
graptolites: 40, 84, 86
mammals: 100-107

reptiles: 89-100
Cladochonus: 51, 52
Cladophyllia: 53
clams: 11, 56, 59. See also pelecypods.
class, taxonomic: 22
classification, binomial nomenclature: 21-22
units of: 22
club mosses: 47
coal: 20, 47
mines: 20, 47
plants: 16, 46, 47, 48
Cochlespiropsis: 63
Coelenterata: 49, 51, 84
coelenterates: 49, 51-53
Coleoidea: 66
coleoids: 77, 78
collecting bags: 17, 18
columella, corals: 51
gastropods: 59, 60
columnal, crinoid: 81, 82, 83
Comanchean series of Cretaceous: 34. See also Lower Cretaceous.
compass: 19
Composita subtilita: 57
compound corals. See corals, colonial.
concretions: 16
coniferous trees: 7
conodonts: 41, 88, 89
Conus: 63
Cooper, G. A.: 2, 12
coprolites: 14
corallite: 49, 51
corallum: 51
corals: 11, 24, 26, 27, 49, 51, 52, 53
“button”: 49, 53
colonial: 24, 27, 30, 51, 52, 53
Cretaceous: 53
“horn”: 49, 51, 52

morphology: 51
Pennsylvanian: 52
polyp: 49
solitary: 24, 28, 29, 30, 49, 51, 52, 53
symmetry: 24, 26, 27, 28, 29, 30
Tertiary: 53
Cordaites: 48
correlation: 32
Corythosaurus: 90
cotylosaurs: 89, 92
crabs: 78, 79
Crassatella: 72
crayfish: 78
creodonts: 102
Cretaceous—
See also Comanchean and Gulf series.
derivation and pronunciation: 34
fossils: 42-43
arthropods: 79
brachiopods: 56
cephalopods: 66, 67, 76, 77
corals: 53
crocodiles: 95, 96
dinosaurs: 90, 91, 93, 94, 95, 97, 99
echinoderms: 83, 84, 85
foraminifers: 49
gastropods: 59, 62
nautiloids: 76
pelecypods: 59, 66, 68-71
shark teeth: 88 117
worms: 78
tubes: 9
of central Texas, Edwards Plateau, Gulf Coastal Plain, High Plains,
north Texas, and Trans-Pecos Texas: 42
“Pyrite Fossil Zone” of: 11
crinoidal limestone: 41, 82, 83
Crinoidea: 81

crinoids: 26, 28, 41, 81, 82, 83
calyx: 81, 82, 83
morphology: 81
stems: 26, 28, 81, 82, 83
Crockett County: 42
Crockett formation: 43
crocodiles: 95, 96
crossopterygians: 87
crustaceans: 79, 80
Culberson County: 35
cuttlefish: 78
cycads: 47, 48
Cymatoceras: 75, 76
Cystoidea: 81
cystoids: 81, 82, 83

D
“Dark Ages”: 3
da Vinci, Leonardo: 3
Davis, Darrell: 1
Decapoda. See Coleoidea.
deer: 106
Del Mar College: 27
dendrites: 14
Dendrograptus: 86
Denver, Colorado: 19
Derbya: 57
Devonian—
derivation and pronunciation: 34
fossils: 41
placoderms: 87, 88
Psilophyton: 48
of El Paso and Van Horn regions, Llano and Marathon uplifts: 41
Diablo Mountains: 41
diatoms: 44, 46, 47
Dibranchiata. See Coleoidea.
Dictyoclostus: 55

Dimetrodon: 92
Dinobastis: 102, 103
Dinocerata: 102
dinocerates: 102, 105
dinosaurs: 89, 90-94, 95, 96, 97, 98, 99, 100
armored: 90, 97, 99, 100
duck-billed: 90, 97, 99
flying: 91, 94, 95
horned: 90, 99, 100
plate-bearing: 90, 97, 99
swimming: 91, 93, 95
Diplodocus: 90
Diplograptus: 86
dire wolf: 102, 103
diris, Canis: 102, 103
distillation: 10
Distorsio: 63
division, plant: 44
Dixon, J. W., Jr.: 2, 90, 91
dolomite: 11
dolphins: 95
domestica, Canis: 22
DuBar, Jules: 1
Dufrenoyia: 77

E
Eastland County: 20
East Texas State College: 27
Echinodermata: 80-84
echinoderms: 80-84
asteroids: 82, 83
blastoids: 81
crinoids: 81, 82, 83
cystoids: 81, 82, 83
echinoids: 82, 84, 85
holothuroids: 84
sclerites: 83

Echinoidea: 82
echinoids: 26, 28, 29, 82, 84, 85
Cretaceous: 84, 85
plates: 84, 85
spines: 84, 85
Echinozoa: 82
Edentata: 100
edentates: 100, 101, 102
Edwards Plateau: 19, 36, 37, 42, 43
Egyptian desert: 3
Elasmosaurus: 91
elephants: 102
Eleutherozoa: 82
Ellison, Samuel P.: 1
El Paso region—
Devonian of: 41
Ordovician of: 40
Precambrian of: 40
Silurian of: 40
Endopachys: 53
Enoploclytia: 79
entelodont: 101, 106
Eohippus. See Hyracotherium.
epoch, geologic: 33
era, geologic: 33-34
Erath County: 20
Eryops: 92
Euomphalus: 61
Euphemites: 62
Europe: 89
Exogyra arietina: 70
laeviscula: 70
ponderosa: 70
texana: 70

F
“false fossils”: 14

family, taxonomic: 22
“feather stars”: 82
ferns: 47, 48
fish: 87, 88, 89
armored: 41, 88
carbon residue: 9
scales: 10
teeth: 10
vertebrae: 10
Fistulipora: 55
Flabellum: 53
foramen, pedicle: 54, 56
Foraminifera: 47, 49
Cretaceous: 49
fusulinids: 26, 29, 49
orbitoid: 26, 28
Pennsylvanian: 49
forams: 26, 28, 29, 47, 49
formation, geologic: 34
fossil—
birds: 5, 100
burrows: 14
cataloging: 31
collecting: 17
equipment: 17 118
ethics: 20
how to collect: 20
where to look: 19
definition: 3
dung: 14
footprints: 14
gizzard stone: 14
identification: 21, 23-30
keys: 26-30
preservation—
altered hard parts: 10-11
carbonization: 9, 10

mineralization: 10
permineralization: 10
petrifaction: 10
replacement, calcareous, iron, siliceous: 10, 11, 13
kinds of: 7
original hard and soft parts: 7
record, missing pages in: 5
wood: 47
fossilization, requirements of: 5
fossils—
animal: 47-107
Cambrian: 40
carbonized: 10
classification of: 21-22
cleaning: 21
etching in acid: 21
frozen: 5, 7, 104
guide and/or index: 32
in amber: 7
in oil saturated soil: 7
in quicksand: 5
in tar: 5
in volcanic ash: 5
main types of: 44
natural mummies: 7
permineralized or petrified: 10
plant: 4, 10, 20, 32, 44-48
Pleistocene: 101, 102, 103, 104
Precambrian: 40
preparation of: 21
Quaternary: 43, 101, 102, 103, 104
replaced or mineralized: 10
silicified: 21
Cretaceous: 11
Permian: 11
etching: 21
Silurian: 40, 81

Tertiary: 43
Triassic: 42
uses of: 31-32
France: 106
Franklin Mountains, Cambrian of: 40
frogs: 89
Frondicularia: 49
fungi: 44
Fusselman limestone: 40
Fusulina: 49
fusulinids: 26, 29, 47, 49
Fusus: 63

G
Gaptank formation: 35, 41
gastroliths: 14
Gastropoda: 56, 59
gastropods: 26, 27, 29, 30, 56, 59, 60
Cretaceous: 59, 62
morphology: 60
ornamentation: 59
Pennsylvanian: 61, 62
Tertiary: 59, 63, 64
generic name: 21-22
genus: 21-22
geologic—
column: 33
history: 33
map, definition: 40
map of Texas: 38-39
time: 34
time scale: frontispiece, 33
geology of Texas: 37-43
Germany: 5, 100
Gingko: 47, 48
Girtyocoelia: 50
Glasscock County: 42

Glass Mountains: 11, 12, 35, 41, 42
glauconite: 11
Globigerina: 49
Glossary: 111-114
Glycymeris: 74
Glyptodon: 101, 102
glyptodont: 101, 102
goats: 106
goniatites: 75, 76
Grand Prairie: 36, 37
Graptolithina: 84, 86
graptolites: 27, 30, 40, 84, 86
of Marathon uplift: 40, 86
Graptozoa. See graptolites.
graysonana, Gryphaea: 69
Great Flood: 3
ground sloths: 7, 101, 102
Gryphaea graysonana: 69
washitaensis: 69
Guadalupe Mountains, Peak: 35
Gulf Coast: 32
Gulf Coastal Plain of Texas: 35, 36, 37, 42, 43, 106
Gulf of Mexico: 37
Gulf series of Cretaceous: 34. See also Upper Cretaceous.
Gyrodes: 62

H
hagfish: 87
hammer, geologist’s: 17, 18
Hamulus: 78
hand lens: 17, 18
hard parts, animal—calcareous, chitinous, phosphatic, siliceous remains: 10
Hardin-Simmons University: 27
heart urchins: 82, 83
Heliospongia: 50
hematite: 11
Hemiaster: 85

Hemichordata: 84
Henderson County Junior College: 27
Herodotus: 3
Heterostegina: 32
Heteralosia hystricula: 12, 13
“het” zone: 32
Hexacoralla: 51
High Plains: 35, 36, 37, 42, 43, 89, 95, 106
hippopotamuses: 106
Holaster: 85
Holectypus: 85
Holothuroidea: 82
holothuroids: 84
sclerites: 83
Homo sapiens: 22 119
“horn corals”: 49, 51, 52
horses: 103, 104
teeth: 104
Howard County Junior College: 27
Hudspeth County: 35, 41, 42
Hueco Mountains: 41
Hughes, Jack T.: 1
hydroids: 49
Hydrozoa: 49, 84
Hyracotherium: 103, 104
hystricula, Heteralosia: 12, 13

I
ichthyosaurs: 91, 93, 95
Ichthyosaurus: 91, 93
identification keys, fossil: 26-30
use of: 23-27
igneous rocks: 5, 19
Inarticulata: 54, 56
Inoceramus: 69
insects: 7, 78, 79
in amber: 7

iron, replacement by: 11
Italy: 3

J
Jack County: 20
jellyfish: 5, 49
Jurassic—
derivation and pronunciation: 34
fossils: 42
birds: 100
dinosaurs: 90, 91, 95, 97, 98, 99
Gingko: 48
of Hudspeth County and/or Malone Mountain: 41
Juresania: 58

K
keys. See identification keys.
Kilgore College: 27
Kingena wacoensis: 56

L
labels, paper: 19
laeviscula, Exogyra: 70
Lamar State College of Technology: 1, 2, 27
lampreys: 87
Latirus: 63
Lee College: 27
Lepidodendron: 46
Levifusus: 64
Lima: 72
limonite: 11
Lingula: 55, 56
Linnaeus: 21
Linné: 21
Linoproductus: 57
lisbonensis, Ostrea: 72
liverworts: 44

lizards: 89
Llano uplift: 36, 37, 40, 41
Lonsdale, John T.: 1
lophophore, brachiopod: 54
Lophophyllidium: 49, 51, 52
proliferum: 52
radicosum: 52
Los Angeles, California: 5
Louisiana: 37
Lower Cretaceous: 34, 42, 56, 97. See also Comanchean.
lugubris, Alectryonia: 68
Lunatia: 62
lungfishes: 87

M
Macon, J. W.: 2
magnifying glass: 17, 18
Malone Mountain: 42
Mammalia: 89, 100-107
mammoths: 102, 104, 107
frozen: 7, 102
tooth: 104
woolly: 102, 104, 107
mantle, brachiopod: 54
pelecypod: 59
maps—
county: 17
geologic: 19
of Texas: 38-39
physiographic of Texas: 36
topographic: 19, 20
Marathon uplift: 35, 36, 40, 41
marcasite: 11
Marginifera: 57
opima: 12, 13
mastodon, tooth: 104
Meandrostia: 50

Mediterranean Sea: 3
mercenaria, Venus: 22
Mesalia: 63
Mesolobus: 57
Mesozoic—
derivation and pronunciation: 33
periods of: 34
rocks in Texas: 42-43
metamorphic rocks: 5, 19
Metoicoceras: 76
Michelinia: 52
Micrabacia: 49, 52
microfossils: 4, 10, 32, 47, 49, 50, 78
micropaleontological slides: 32
micropaleontologist: 32, 47, 80
micropaleontology: 4, 89
Midwestern University: 27
mine dumps: 20, 47
Mississippian—
derivation and pronunciation: 34
fossils: 41
blastoid: 81
brachiopods: 55
bryozoan: 54
of Hueco Mountains: 41
of Llano region: 41
mold, external: 9, 11, 59, 66
internal: 9, 11, 59, 62, 66
Mollusca: 56-78
mollusks: 7, 56, 59-78. See also Mollusca.
Moropus: 106
mosasaur: 91, 93, 95
“moss animals”: 54
mosses: 44
Muirwoodia multistriatus: 12, 13
multituberculates: 100
multistriatus, Muirwoodia: 12, 13

mussels: 56, 59
museums, as aid in identification: 23
American, Natural History: 2, 15, 96
Strecker: 95
Texas Memorial: 14, 87, 95, 97, 100, 102
Myalina: 67
Mylodon: 100, 101

N
Nautiloidea: 66
nautiloids: 66
Cretaceous: 76
morphology: 75
Pennsylvanian: 76 120
sutures: 75
Nautilus: 66
morphology: 75
Neithea: 70
Neospirifer: 57
cameratus: 58
Nerinea: 62
Neuropteris: 48
Neverita: 64
New Mexico: 7
New York City: 14
North-Central Plains: 35, 36, 37, 40, 41, 42, 43
north Texas: 42
North Texas State College: 27
notebook, field: 17
Notopocorystes: 79, 80
Nucula: 73
Nuculana: 67
Nuculopsis: 67

O
octopus: 66, 78
Odessa College: 27

operculum: 59
Ophiuroidea: 82
ophiuroids: 82
opima, “Marginifera”: 12, 13
order, taxonomic: 22
Ordovician—
derivation and pronunciation: 34
fossils: 40
graptolites: 86
of El Paso region, Llano, Marathon, Solitario, and Van Horn uplifts: 40
ornamentation, brachiopod: 54
gastropod: 59
pelecypod: 66
Ornithischia: 97
ornithischians: 90, 97, 98, 100
Ornithopoda: 97
ornithopods: 90, 97, 99
Orthoceras: 66, 76
Orthoyoldia: 73
ossicles. See sclerites.
Osteichthyes: 87
Ostracoda: 80
ostracoderms: 87
ostracodes: 78, 79, 80
Ostrea carinata: 71
lisbonensis: 72
quadriplicata: 71
sellaeformis: 72
Oxytropidoceras: 77
oysters: 56, 59

P
Pachecoa: 72
Pachymya: 71
paleobotany: 4
paleobotanists: 44
paleontology—

definition: 4
divisions of: 4
history of: 3
invertebrate: 4
vertebrate: 4
Paleoscincus: 90, 97, 99, 100
Paleozoic—
derivation and pronunciation: 33
periods of: 34
rocks of Texas: 40-42
Palo Pinto County: 20
Paluxy Creek: 14, 15
Pan American College: 27
Pantodonta: 102
pantodonts: 102
Parasaurolophus: 90
Parasmilia: 53
Parker County: 20
Pawpaw formation: 11
pearly nautilus: 66
morphology: 75
Pecos County: 42
Pecos River valley: 35
Pecten: 59, 68, 74
pedicle: 54, 56
foramen: 54, 56
valve, brachiopod: 54
Pelycosaurs: 89, 92
Pelecypoda: 56, 59, 65-66
pelecypods: 26, 29, 30, 56, 59, 60, 66
Cretaceous: 59, 66, 68-71
dentition: 66
morphology: 59, 60, 65, 66
ornamentation: 66
Pennsylvanian: 66, 67
teeth: 60, 65, 66
Tertiary: 72, 73, 74

Pelmatozoa: 80, 81
Pennsylvanian—
derivation and pronunciation: 34
fossils: 41
brachiopods: 57, 58
bryozoans: 55
cephalopods: 66, 76
corals: 52
crinoids: 41, 82, 83
fusulinids: 47, 49
gastropods: 61, 62
nautiloids: 76
pelecypods: 66, 67
plants: 46, 47, 48
shark teeth: 87
sponges: 50
of Diablo and Hueco Mountains, Llano and Marathon uplifts, and
north-central Texas: 41
Pentaceros: 83
Pentagonaster: 83
Pentremites: 81
period, geologic: 33
periostracum: 60
Perissodactyla: 104
perissodactyls: 103, 104, 105
Permian—
derivation and pronunciation: 34
fossils: 41
amphibian: 89, 92
brachiopods: 12, 13
cotylosaurs: 89, 92
pelycosaurs: 89, 92
of Glass Mountains: 11, 12, 35
permiana, Prorichthofenia: 12, 13
permineralized bone: 9
petroleum geologist: 4
Phaneroceras: 76

Phobosuchus: 95, 96
Pholadomya: 71, 72
phyla: 22
Phyllograptus: 86
phylum: 22
physiographic provinces, of Texas: 35-37
physiography, definition: 35
of Texas: 35-37
phytosaurs: 42, 91, 94, 95 121
pick, mineralogist’s or prospector’s: 17, 18
pigs: 106
Pinna: 67
Pisces: 86-89
Pitar: 72
Placodermi: 87
placoderms: 87, 88
plant kingdom: 44
plants, classification: 44
Pennsylvanian: 46, 47, 48
Platyceras: 62
Pleistocene: 43. See also Quaternary.
fossils: 101, 102, 103, 104
plesiosaurs: 91, 93, 95
Pleurocora: 53
Plicatula: 68, 74
Pliohippus: 103
Poland: 7, 106
pollen: 47
polyp, coral: 49
Polypora: 55
ponderosa, Exogyra: 70
Porifera: 49
Porodiscus: 49
portland cement: 19
Precambrian—
definition: 34
fossils: 40

of El Paso region: 40
of Llano uplift: 37, 40
of Van Horn uplift: 40
rocks of Texas: 40
Presidio County: 35
Proboscidea: 102
proboscideans: 102, 104, 107
teeth: 104
proliferum, Lophophyllidium: 52
Prorichthofenia permiana: 12, 13
Proterozoic, derivation and pronunciation: 33
Protista: 47
Protocardia: 68
Protoceratops: 90
Protozoa: 47, 49
protozoans: 47
pseudofossils: 14
Pseudoliva: 63
Psilophyton: 48
Pteranodon: 91, 94
Pterodactyloids: 91
pterosaurs: 91, 94, 95
Punctospirifer: 57
pyrite: 11
“Pyrite Fossil Zone” of Cretaceous: 11

Q
quadriplicata, Ostrea: 71
quarries: 19
Quaternary—
derivation and pronunciation: 34
fossils: 43, 101, 102, 103, 104
of Edwards Plateau, Gulf Coast, High Plains, North-Central Plains,
and Trans-Pecos Texas: 43
quicksand: 5

R

radicosum, Lophophyllidium: 53
Radiolaria: 47
radiolarians: 47, 49
Rancho La Brea tar pit: 5
rays: 87
Reagan County: 42
Receptaculites: 50
Renaissance: 3
Reptilia: 89-100
reptiles: 89-100
rhamphorhynchoids: 91
Rhamphorhynchus: 91, 94
rhinoceroses: 7, 104, 106, 107
woolly: 106, 107
Rhipodomella: 55
Rhombopora: 51, 55
Rice University: 27
Rio Grande valley, of Trans-Pecos: 35, 95
road metal: 19
Robulus: 49
Rock and Mineral Clubs: 23
rock units: 34
rockymontanus, Spirifer: 58
Rodda, Peter U.: 1
rudistids: 26, 27, 28, 29, 30
Rugosa: 51

S
saber-tooth cat: 102, 103
St. Mary’s University: 27
salamanders: 89
Salenia: 85
San Angelo College: 27
San Antonio College: 27
sand dollars: 82
sapiens, Homo: 22
Sarcodina: 47

Saurischia: 97
saurischians: 90, 97, 99
Sauropoda: 97
sauropods: 90, 97, 98
scale trees: 46, 47
scallops: 56, 59
Scaphopoda: 56
scaphopods: 26, 27, 28, 29, 56
Schizodus: 67
scientific names: 21-23
Scleractinia: 51
sclerites, holothurian: 83, 84
scolecodont: 78
scouring rushes: 47, 48
Scyphozoa: 49, 84
sea anemones: 49
sea cucumbers: 82
“sea lily”: 81, 82
“sea mats”: 51, 54
“sea-mice”: 56
sea urchins: 82
sedimentary rocks: 5, 19
sellaeformis, Ostrea: 72
septa, cephalopods: 66, 75
corals: 49, 51
serpent stars: 82
Serpula: 78
Seymouria: 92
sharks: 87
teeth: 10, 87, 88
sheep: 106
shrimp: 78
Siberia: 7, 106
Sigillaria: 46
signata, Avonia: 12, 13
silica: 10, 11
silicification: 11

Silurian—
derivation and pronunciation: 34
fossils: 40
cystoid: 81
of El Paso and Van Horn regions: 40
skates: 87 122
slickensides: 16
slugs: 56
Smith, Fred: 1
snails: 11, 56, 59. See also gastropods.
snakes: 89
Solitario uplift: 40
Somervell County: 14, 15
South America: 87, 102
Southern Methodist University: 27
South Texas College: 27
Southwestern University: 27
species: 22
spicules, sponge: 49, 50
spiders: 78
spines, echinoid: 84, 85
Spirifer rockymontanus: 58
Spirorbis: 78
sponges: 10, 27, 30, 49, 50
spores: 47
Squamularia: 57
squid: 66, 78
starfish: 82, 83
Stegosaurus: 90, 97, 99
stegosaurs: 90, 97, 99
steinkern: 59, 62
stems, crinoid: 26, 28, 41, 81, 82, 83
Stephen F. Austin State College: 27
“stomach stones”: 14
stone, building: 19
Strabo: 3
Straparolus: 61

Strecker Museum: 95
Striatopora: 51, 52
Strobeus: 62
Styracosaurus: 90
subhorrida, Avonia: 12, 13
subtilita, Composita: 57
Sul Ross State College: 27
Surcula: 64
sutures, cephalopod: 66, 75, 78
nautiloid: 75
swine, giant: 106
Sycostoma: 64
symmetry: 23
bilateral: 24, 26, 29
radial: 24, 26, 28, 80

T
tabulae: 51
Tabulata: 51
tape, masking: 19
tapirs: 104
tar: 5
Tarleton State College: 27
Tarrant County: 11
taxonomy: 21-22
teeth, horse: 104
mammoth: 104
shark: 10, 87, 88
Tellina: 73
Tertiary—
derivation and pronunciation: 34
fossils: 43
corals: 53
gastropods: 59, 63, 64
mammals: 100-107, 103, 105
microfossils: 32
pelecypods: 72, 73, 74

radiolarians: 49
rocks of Gulf Coastal Plain, High Plains, North-Central Plains,
and Trans-Pecos region: 42
Tetracoralla: 51
Tetrapoda: 86, 89-107
texana, Exogyra: 70
Texanites: 77
Texas A. & M. College: 1, 27
Texas Christian University: 27
Texas College: 27
Texas College of Arts and Industries: 27
Texas Highway Department: 17
Texas Memorial Museum: 14, 87, 95, 97, 100, 102
Texas Technological College: 27
Texas, the geology of: 34, 37-43
Texas Western College: 27
Thallophyta: 43, 46
Theophrastus: 3
Therapsids: 89
Theria: 100
therians: 100-107
artiodactyls: 101, 106
carnivores: 102, 103
dinocerates: 102, 105
edentates: 100, 101, 102
pantodonts: 102
perissodactyls: 104
proboscideans: 102, 104, 107
Theropoda: 97
theropods: 90, 97, 98
The University of Texas: 1, 2, 27
time, geologic: 34
titanotheres: 104, 105, 106
toads: 89
tortoises: 89
traces of organisms: 14
burrows: 14

coprolites: 14
gastroliths: 14
tracks: 14, 15
trails: 14
Tracheophyta: 44, 46, 48
Trachodon: 90, 97, 99
tracks, dinosaur: 14, 15, 97
Trans-Pecos region: 35, 36, 40, 42, 43, 86, 95, 102, 106
tree sloths: 100, 102
trees, coniferous: 7
Trepospira: 61
Triassic—
derivation and pronunciation: 34
fossils: 42
dinosaurs: 95
phytosaurs: 91, 94, 95
of Crockett, Glasscock, Pecos, Reagan, and Upton counties; Glass
Mountains and High Plains: 42
Triceratops: 90, 99, 100
Trigonia: 69
Trilobita: 78
trilobites: 78, 80
morphology: 80
Trilobitomorpha: 78
Trinacromerum: 91
Trinity University: 27
trivial name: 21-22
Trochosmilia: 53
Tuba: 64
tuberculatus, Aulosteges: 12, 13
Turrilites: 77
worthensis: 22
Turritella: 62, 63 123
turtles: 89, 91
tusk-shells: 56
Tyler Junior College: 27
Tylosaurus: 91, 93

Tylostoma: 62
Tyrannosaurus: 90, 97

U
uintatheres: 102, 105
Uintatherium: 102, 105
umbilicus: 59, 60
United States Geological Survey: 19
United States National Museum: 2, 12
University of Corpus Christi: 27
University of Houston: 1, 27
University of Texas, The: 1, 2, 27
Upper Cretaceous: 34, 42, 78. See also Gulf.
Upton County: 42

V
valves, brachiopod: 54, 56
pelecypod: 59, 65, 66
Van Horn uplift: 35, 36, 40, 41
Venericardia: 73
bulla: 72
ventral valve, brachiopod: 54
Venus mercenaria: 22
Vertagus: 63
Vertebrata: 84, 86-107
vertebrates: 86-107
amphibians: 89, 92
birds: 100
fish: 87, 88, 89
mammals: 100-107
reptiles: 89-100
Vokesula: 73
volcanic ash: 5
Volutolithes: 64

W
Waco: 91, 92, 95

wacoensis, Kingena: 56
Washington, D. C.: 19
washitaensis, Gryphaea: 69
Weches formation: 43
West Texas State College: 1, 27
Wilson, John A.: 2
Wilson, Sarah Louise: 2
Wise County: 20
wood, petrified: 19
Woodbine: 10, 37, 47
worms, annelid, fossil, segmented: 78
worm tubes, Cretaceous: 9
Worthenia: 61
worthensis, Turrilites: 22

Y
Yoldia: 67
Young County: 20
Young, Keith: 1

Z
Zoantharia: 51
zooecia: 51

Transcriber’s Notes

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