orthoceras
/ɔːˈθɒsəras/Palaeontology
noun
A fossil orthoconic shell of a nautiloid cephalopod mollusc of the Palaeozoic or early Mesozoic eras; specifically a member of the genus Orthoceras.
Origin
Mid 18th century; earliest use found in Philosophical Transactions of the Royal Society of London. From post-classical Latin Orthoceras from ancient Greek ὀρθο- ortho- + κέρας horn.