Nautiloid cephalopods are widely distributed in the Tertiary strata of North, Central, and South America and the West Indies. Geographically they range from Alaska on the north to Tierra del Fuego on the south, and stratigraphically they extend throughout all the Tertiary, though they seem to be rare indeed in the Pliocene. Locally they are abundant in the Early Tertiary of southeastern United States and northwestern Peru, but elsewhere they are sporadic.
All have nautiliconic conchs and orthochoanitic siphuncles and none bears prominent ornamentation. Modern Nautilus, which extends back to the Eocene and which is more or less typical of the Tertiary forms, helps us to understand their habits, habitat, anatomy, shell, etc.
Altogether some 75 species of nautiloids are known from the Tertiary of the Americas (including the West Indies). On the basis of the form of the conch, the position of the siphuncle, and particularly the shape of the sutures, these can be divided into three families: (1) the Nautilidae, which includes Nautilus and Eulre-phoceras; (2) the Hercoglossidae, which includes Cimomia, Hercoglossa, Deltoido-nautilus, Woodringia, and Aluroidea; and (3) the Aturidae, which has only one generic representative, Aturia. Half of these genera are not known to occur above the Eocene; but Eulrephoceras and Cimomia extend up into the Oligocene, Aturia ranges up into the Miocene, and Nautilus (which is not known to be represented in the American Tertiary) is still extant.