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.