Chapter II: Introduction (1)

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 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.

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 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.

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 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.

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.

Figures—
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 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 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.

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

Figures—
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

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.

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.

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

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.

Slickensides

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.

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).

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

Other Useful Items

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 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.

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 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.

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 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).

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 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.

IDENTIFICATION KEY TO MAIN TYPES OF INVERTEBRATE FOSSILS

(Instructions on pages 23-25 for use of key)