An extinct marine invertebrate belonging to the Class Trilobita of the Phylum Arthropoda, and characterized by a three-part body and an exoskeleton divided longitudinally into three lobes. Trilobites were one of the most successful early animals, crawling over the ocean floor for over 270 million years until they went extinct at the end of the Paleozoic Era, 252 million years ago.
Trilobites were primitive arthropods distantly related to horseshoe crabs. As bottom dwellers, they were present in a variety of environments. Like crabs and lobsters, trilobites molted their exoskeletons when they grew. Most fossils of trilobites are actually molts, broken as they were shed off the trilobite. Thus, it is common to find only parts of trilobites, such as the head, mid-section, or tail.
