Trilobites are extinct arthropods in the class Trilobita. They appeared in the Cambrian era and flourished throughout the lower Palaeozoic before slowly declining to extinction. The last of the trilobites disappeared in the mass extinction at the end of the Permian. Trilobites are well-known, possibly the second most famous fossil group after the dinosaurs, and are the most diverse group of animal species preserved in the fossil record, consisting of eight, possibly nine, orders and over 15,000 species. Most were simple, small marine animals that filtered mud to obtain food.