Part 8

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)

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) 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

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

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

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

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

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 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.