Nautilidae

The Nautilitidae is the principal family of the nautilid superfamily Nautilaceae and of its smaller but near equal suborder, the Nautilina. (Kummel 1964)

Nautilidae are characterized by involute or slightly evolute shells that are generally smooth, with compressed or depressed whorl sections, straight to sinuous sutures, and a tubular, generally central siphuncle. (ibid)

Phylogeny

The Nautilidae has its origin in the Trigonocerataceae (Centroceratina), specifically in the Syringonautilidae of the Late Triassic (Kummel 1964)and continues to this day with Nautilus, the type genus and its close relative, Allonautilus.

Fossil Genera

The Nautilidae begin with Cenoceras in the Late Triassc, a hightly varied genus that makes up to Jurassic Cenoceras complex. Cenoceras is evolute to involute, and globular to lentincular; with a suture that generally has a shallow ventral and lateral lobe and a siphuncle that is variable in position but never extreemly ventral or dorsal. Cenoceras is not found above the Middle Jurassic and is followed by the Upper Jurassic -Miocene Eutrephoceras.

Eutrephoceras is generally subgobular, broadly rounded laterally and ventrally, with a small to occluded umbilicus, broadly rounded hyponomic sinus, only slightly sinuous sutures, and a small siphuncle that is variable in position.

Next to appear is the Lower Cretaceous Strionautilus from Indea and the European ex-USSR, named by Shimankiy in 1951. Strionautilus is compressed, involute, with fine longitudinal striations. Whorl sections are subrectangular, sutures sinuous, the siphuncle subcentral.

Also from the Cretaceous is Pseudocenoceras, named by Spath in 1927. Pseudocenoceras is compressed, smooth, with subrectangular whorl sections, flattened venter, and deep umbilicus. The suture crosses the venter essentially straight and has a broad, shallow, lateral lobe. The siphuncle is small and subcentral. Pseudocenoceras is found in the Crimea and in Libia.

Carinonautilus is a genus from the Upper Cretaceous of India , named by Spengler in 1919.Carinonautilus is a very involute form with high whorl section and flanks that converge on a narrow venter that bears a prominent rounded keel. The umbilicus is small and shallow, the suture only slightly sinuous. The siphuncle is unknown.

Finally there is the discoidal and very involute Obinautilus, with rapidly expanding and compressed whorls, fine radial ribs, rounded venter with shallow furrow, and almost closed umbilicus, named by Kobayashi in 1954, from the Oligocene of Japan.