The Nautilina is the last suborder of the

Nautilida The Nautilida constitute a large and diverse order of generally coiled nautiloid cephalopods that began in the mid Paleozoic and continues to the present with a single family, the Nautilidae which includes two genera, ''Nautilus'' and ''Allonauti ...

and the only

nautiloids Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded species ...

living since the end of the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

. The Nautilina, proposed by Shimanskiy, is basically the

Nautilaceae The Nautilaceae form one of five superfamilies that make up the Nautilida according to Bernard Kummel (1964), and the only one that survived past the Triassic. The Nautilaceae comprise six families: Nautilidae, Paracenoceratidae, Pseudonautilidae ...

of Kummel, 1964, defined by Furnish and Glenister, but differs in omitting two families, the

Paracenoceratidae The Paracenoceratidae are an extinct family of prehistoric nautiloids. The cephalopods lived during the Jurassic and Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the thi ...

and Pseudonautilidae which instead are placed in the

Liroceratina The Clydonautiloidea are a superfamily within the nautiloid order Nautilida characterized by smooth, generally globular, shellsKummel 1964; Nautiloidea -Nautilida, Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontol ...

. The Nautilina are derived from the Syringonautilidae, a family in the

Centroceratina The Trigonoceratoidea are a superfamily within the Nautilida that ranged from the Devonian to the Triassic, thought to have contained the source for the Nautilaceae in which ''Nautilus'' is found. Trigonoceratoidea are characterized by open-sp ...

(Trigonocerataceae), in the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...

and consists of four families, the Nautilidae, Cymatoceratidae, Herocoglossidae, and Aturiidae. The Nautilidae, which is the root stock of the suborder, includes the living ''

Nautilus The nautilus (, ) is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species in t ...

''. The Nautilidae are

involute In mathematics, an involute (also known as an evolvent) is a particular type of curve that is dependent on another shape or curve. An involute of a curve is the locus of a point on a piece of taut string as the string is either unwrapped from or ...

or slightly evolute and generally smooth with straight to sinuous sutures. The Cymatoceratidae, which are the most common of the Cretaceous nautiloids, are strongly ribbed. The Hercoglossidae are smooth but with differentiated sutures, in some with deep lateral lobes and well-developed saddles. The Aturiidae (Aturia) is similar to the Hercoglossidae except for being more discoidal and having a more complex suture and subdorsal

siphuncle The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and ...

. The Nautilidae gave rise to the Cymatoceratidae and Hercoglossidae during the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

while the Herocoglossidae became ancestral to the Aturiidae near the beginning of the

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

. The Cymatoceratidae and Hercoglossidae became extinct near the end of the

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

while the Aturiidae reached into the

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...

. Only the Nautilidae remain.

References

* Kummel, B., 1964; Nautilidea-Nautilida, in the Treatise on Invertebrate Paleontology, Part K Nautiloidea; Geological Society of America and Univ. of Kansas press. Teichert and Moore eds. {{Taxonbar, from=Q3523153 Nautiloids Extant Late Triassic first appearances