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. 4]a).
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. 4]a, 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 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.