Category: Mollusca Class: Cephalopoda The genus orthoceras (from Greek, ortho = straight; ceras = horn) inhabited the seas between the Ordovician Period and the Triassic Period. Some specimens reached large sizes, comparable to today's giant squids. One of the most characteristic and largest species was Orthoceras regulare. The currently best-known Orthoceras fossils come from Erfoud, in the Atlas Mountains of Morocco.
