Orthoceras fossils are the remains of an invertebrate, no backbone, that belongs to the Phylum Mollusca. This is a broad grouping of animals that include snails, slugs, oysters, clams, octopus, and squid.
The phylum is broken down into classes. Orthoceras belongs to the class Cephalopoda. Other living members of this class are octopus, squid, and the chambered nautilus. The name cephalopoda means head foot referring to the fact that their tentacles or feet grow out of their heads.
The subclass of orthoceras is Nautiloidea. This really narrows the field. The only living member is the Chambered Nautilus. Extinct members of this subclass include the ammonites.
Of course the subclasses are broken down further into orders. Orthoceras belongs to the order Orthocerida. This order is characterized by their long straight conical shells. The shells could be smooth or ribbed.
Up to now classification issues have been fairly straight forward. But when it comes to family and genus names for orthoceras fossils there is disagreement. Orthoceratidae is the family name, though some sources call the family name Michelinoceratidae. The disagreement has to do with the time period the orthoceras fossils come from and the geographic location in which they are found.
To further confuse the issue all members of the order Orthocerida are commonly referred to as orthoceras. Proper claim to the name appears to be for the species Orthoceras regulare. In this case common usage seems to predominate.
Species: Orthoceras regulare