Some of the most familiar and spectacular fossils of the geological record belong to the cephalopods. Although the living cephalopods, as a group, are mostly the shell-less octopi and squid, throughout geological history the fossil record has been dominated by species with external or internal shells. Cephalopods are characterized by a well-developed head, generally large brain and eyes, and a series or arms or tentacles. The shells may be straight or coiled. Even or contorted sutures are usually visible on the outside of the of the shell marking the internal septae.
Cephalopods are marine and predaceous.
The cephalopods occur in the fossil record from the late Cambrian to the Recent. The cephalopods are divided into six primary orders. The chambered nautilus of poesy fame is a living representative of the nautiloids, but the group was best represented in the Paleozoic. The fossil record stretches from the Cambrian to the Recent. Ammonites are some of the most fascinating fossils to be found and are incredibly diverse.