Fossilized Trilobite 

The study of complex creatures that inhabited the Earth millions of years ago takes us to the trilobite. Trilobites were the first complex creatures to possess a hardened exoskeleton. During the Cambrian period which began some 570 million years ago, an estimated 10,000 species of trilobites existed. At the end of the Paleozoic Era about 220 million years ago. trilobites became extinct. Today, the only way we can about these interesting creatures is by studying their fossil remains. 

Trilobites had three lobes, or segments: cephalon (head); thorax (body); and pygidium (tail.) They range in size from 0.2" up to as large as 2 feet long. Genus: Phacops