Trilobites are one of the most common fossils found. They are extinct oceanic arthropods that lived between 345 and 315 million years ago. The mass extinction which occurred at the end of the Permian period wiped them all out, but their exoskeletons ensured that they would be well-preserved, and their numbers can be assumed to have been very numerous when they were in their prime.

A trilobite is extinct marine arthropod which existed in the Paleozoic Era. There are many species of these creatures which had segmented bodies and hard shells. You can find more information here: http://www.trilobites.info/trilobite.htm...