Part 13

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.

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

DIATOMS × 900 ALGAE × 400

LEPIDODENDRON × ½ SIGILLARIA × ½

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

Fairly well-preserved plant remains may also be collected from the 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.—