Orthocone

An orthocone is the long, cone-shaped shell belonging to several species of ancient nautiloid cephalopod—the prehistoric ancestors of today's marine cephalopod mollusks, including the cuttlefishes, nautili, octopi and squids.^[1] During the 18th and 19th centuries, all such shells discovered were given the "catch-all" name Orthoceras, thus creating a wastebasket taxon. However, it is now known that many species, genera and families of nautiloids developed or retained this form of shell.

An orthocone, loosely, may be thought of as a nautiloid shell, albeit somewhat larger and with a cone-shaped, straight formation as opposed to the nautiloid's coiled, curled shape. It was previously believed that these represented the most primitive form of nautiloid, however, it is now known that the earliest nautiloids had shells that were slightly curved. An orthoconic form evolved several times among cephalopods, and, among nautiloid cephalopods, is prevalent among the ellesmerocerids, endocerids, actinocerids, orthoceratoids, and bactritids.

Orthocones existed from the Late