Orthocerida

Orthocerida, from Ancient Greek ὀρθός (orthós), meaning "straight", and κέρας (kéras), meaning "horn", also known as the Michelinocerida, is an order of extinct orthoceratoidcephalopods that lived from the Early Ordovician to the Late Permian. While there has been some possible Late Triassic records for the order, although they have been reclassified as pseudorthocerids. The Eocene fossil Antarcticeras is sometimes considered a descendant of the orthocerids although this is disputed. They were most common however from the Ordovician to the Devonian.

A fossil found in the Caucasus was previously assigned to Orthocerida, extending the range to the Early Cretaceous, but has since been reassigned to the order Mixosiphonata.