Orthocone

Orthocone is a usually long straight shell of a nautiloid cephalopods. During the 18th and 19th centuries, all shells of this type were named Orthoceras, but it is now known that many groups of nautiloids dffeveloped or retained this type of shell.

An Orthocone can be thought of as like a nautilus shell, but with the shell straight and uncoiled. It used to be thought that these represented the most primitive form of nautiloid, but it is now known that the earliest nautiloids had shells that were slightly curved.

Orthocones characterised nautiloids from the Early Ordovician to the Late Triassic, although they were most common in the early Paleozoic. They range in size from less than an inch to (in some giant Endocerids of the Ordovician) seventeen feet long.