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).
[Illustration: Fig. 4. Types of symmetry in a fossil coral. (a) Radial
symmetry. (b) Bilateral symmetry.]
[Illustration: 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.