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, nautiluses, octopuses and squids.

[2] Revivals of the orthocone design later occurred in other cephalopod groups, notably baculitid ammonites in the Cretaceous Period.

A potential Cenozoic orthocone is known in Antarcticeras, which may be a descendant of the orthoceratoids and has an orthocone-like shell that is thought to have been weakly mineralized and internal, in contrast to the external, fully-mineralized shells of earlier orthocones—an example of convergent evolution with the coleoids.

[3] Orthocone nautiloids range in size from less than 25 mm (1 in) to (in some giant endocerids of the Ordovician) 5.2 m (17 ft) long.

Orthocone cephalopod fossils are known from all over the world, with particularly significant finds in Ontario, Canada and Morocco.