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 (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

. The Nautilina, proposed by Shimanskiy, is basically the Nautilaceae 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 (Trigonocerataceae), in the

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

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

Jurassic The Jurassic ( ) is a geologic period and 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 Jurassic constitutes the middle period of ...

while the Herocoglossidae became ancestral to the Aturiidae near the beginning of the Cenozoic. The Cymatoceratidae and Hercoglossidae became extinct near the end of the Paleogene while the Aturiidae reached into the Neogene. 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