Cephalopods are known from the Cambrian Period to the present. This class of marine invertebrate animals includes modern squids, octopuses, cuttlefishes, and nautiluses. The term cephalopod is from Greek, meaning "head foot."

Fossils of cephalopods typically are only the shells of the animals. Soft parts, such as the head and tentacles, are only exceptionally preserved as fossils. Consequently, the fossil record of cephalopods lacking shells is poor. Cephalopod shells have had a variety of shapes: coiled, curved (cyrtoconic), and straight (orthoconic). Shells offered protection and also allowed cephalopods to control their buoyancy in the water column.

In Ohio, fossil cephalopods have been identified in Ordovician to Pennsylvanian marine rock units.

The genera and/or species listed are representative only; species found in Ohio are too numerous to list here. For identification of genera and species, refer to Bulletin 70: Fossils of Ohio (see Additional Information).