William Henry Matthews

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”