520- 250 million years old, trilobites are an extinct marine arthropod – a family including present-day crustaceans and spiders. There are thousands of known species of trilobites ranging in size from 1 mm to over 2 feet. Trilobite bodies are characterized by three lobes (tri-lobe): the cephalon (head), thorax (body), and pygidium (tail). They were among the first animals to develop complex, compound eyes, with lenses made of calcite. Trilobite fossils are found on every continent; locations include Utah, New York, and Morocco.