Trilobites (Trilobita) (meaning "three lobes") were a class of arthropods that appeared in the early Cambrian period (526 million years ago) and died out in the Permian–Triassic (P–Tr) extinction event at the end of the Permian period (about 250 million years ago). Trilobites were marine animals so they lived only in the oceans.

Trilobites are among the most succesfull animals of all times they survived such a long time and were common for millions of years. Most species were small but Largest trilobite Isotelus rex was about 720 millimetres or 28 inch long.

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