trilobites occur in rocks of the ordovician age on white background.

sample nautiloids fossils rock isolated white background ordovician period group marine cephalopods common found kentucky include sponges porifera corals cnidaria bryozoans brachiopods trilobites snails gastropods clams pelecypods squid-like animals crinoids echinodermata microscopic ostracodes conodonts trilobite age sand occur rocks