''Styrionautilus'' is a genus of nautiloids and first of the

Clydonautilidae The Clydonautilidae are Middle and Upper Triassic nautiloid cephalopods, which are derivatives of the clydonautiloidean family Liroceratidae, that have generally smooth, involute, globular to compressed shells, characterized by a suture with p ...

with a range extending from the Middle Triassic, Anisian to the Upper Triassic,

Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic defi ...

. Its fossils have been found in North America (Nevada), Europe, and Timor. In general form ''Styrionautilus'' is similar to other clydonautilids, smooth and involute. The suture however is more primitive. The ventral saddle is straight across without modification of a median lobe. ''Styrionautilus'' may be derived from '' Indionautilus'' or similar form included in the

Liroceratidae Liroceratidae is an extinct family of nautilids, shelled marine molluscs, belonging to the Clydonautiloidea, consisting of generally smooth, involute, nautiliconic forms with a small umbilicus. The whorl section is usually depressed and broad ...

. In turn ''Styrionautilus'' is the likely ancestor of ''

Proclydonautilus ''Proclydonautilus'' is a genus of nautiloids belonging to the Clydonautilidae known from the Upper Triassic of North America, Europe, and India. The shell of ''Proclydonautilus'', like those of other Clydonautilitidae, is involute and smooth. ...

'', ''

Cosmonautilus ''Cosmonautilus'' is a genus of cephalopods included in the nautilid family Clydonautilidae. Its shell is involute, with only the outer whorl exposed. Early whorls are with nodes on ventral shoulder, which disappear on the later growth staged. ...

'', and/or ''

Callaionautilus ''Callaionautilus'' is a genus of cephalopods included in the nautilid family Clydonautilidae that lived during the Late Triassic. Its fossils have been found on the island of Timor. The shell of ''Callaionautilus'' is involute, coiled such tha ...

References

* Bernhard Kummel, 1964. Nautiloidea-Nautilida. Treatise on Invertebrate Paleontology, Part K. Geological Society of America.
''Styrionautilus''
in Fossilworks gateway. * J.J. Sepkoski 200
Online list of cephalopod genera
Prehistoric nautiloid genera Anisian genus first appearances Ladinian genera Carnian genera Norian genus extinctions Anisian life {{paleo-nautiloidea-stub