Modica sp.-Utah

Trilobites lived from the Cambrian into the Permian. There are over 25,000 known species and their hard exoskeleton is the reason we have such a good understanding of these animals. Trilobite (“three lobed”) are extinct arthropods. Their bodies were devided into three parts: the cephalon (head), the body (thorax), and the pygidium (tail). Trilobite fossils are found worldwide, with many thousands of known species. Because they are so common, trilobites serve as excellent index fossils. This means that identifying the type of trilobite enables geologist to date and age the rocks in which they are found. When threatened some trilobites acted much like today's pillbugs—tucking in their legs and antennae, by bending the thorax and bringing the tail underneath the head. Trilobites roll up in a ball for protection providing additional protection for the appendages and soft parts.

Modica sp., Middle Cambrian, Marjum fm., Millard Co., Utah