Trilobites flourished in the shallow-marine environments of Cambrian time. Some 600 different species of them are believed to have lived in Cambrian Period. Throughout this time period, they became increasingly diversified. Geologists use Trilobite fossils to determine the age of rocks, because they had such a consistent evolution and because of their abundant fossils. Why are trilobite fossils so common? Actually, it often it is not the trilobite that is found, but its exoskeleton, which was frequently shed in order to grow. Also, trilobites are believed to be the most common animal, besides bacteria, to have lived in Cambrian time. Early trilobites are thought to have been mud eaters or scavengers living on the bottom of the oceans. Most of them probably crawled their way around on the ocean floor.

A fossil trilobite