The Pseudonautilidae is a family of Jurassic

Jurassic

The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 and Lower Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 cephalopod

Cephalopod

A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...

s belonging to the same major group as modern Nautilus

Nautilus

Nautilus is the common name of marine creatures of cephalopod family Nautilidae, the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species in two genera, the type of which is the genus Nautilus...

, the Nautilaceae

Nautilaceae

The Nautilaceae is one of five superfamilies that make up the Nautilida according to Bernard Kummel , and the only one that survived past the Triassic. The Nautilaceae comprise six families: Nautilidae, Paracenoceratidae, Pseudonautilidae, Cymatoceratidae, Hercoglossidae, and Aturiidae...

, but forming a different branch from the Nautilidae. They were contemporary with ammonites (order Ammonitida

Ammonitida

The Ammonitida is an order of more highly evolved ammonoid cephalopods from the Jurassic and Cretaceous time periods, commonly with intricate ammonitic sutures....

) which comprise an entirely different set of shelled cephalopod stocks.

Pseudonautilids are characterized by an involute, generally compressed, nautiliconic shell; highly sinuous "goniatitic" sutures; and siphuncle

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 Spirula...

 generally located between the center and venter. Three genera are included.

• Pseudonautilus: Shell involute, compressed; whorl section higher than wide, flanks flattened; venter broadly arched; umbilicus small and deep; suture with deep narrow ventral lobe, large V-shaped lateral lobes on either side followed by rounded saddles then smaller lobes just above the umbilical seam; siphuncle subventral. Found in Europe and North Africa. An almost perfect homeomorph of the Permian Permoceras
  Permoceras
  Permoceras, the sole member of the Permoceratidae, is a coiled nautiloid with a smooth, compressed involute shell, whorls highter than wide, earlier whorls hidden from view. The venter is rounded as are the ventral and umbilical shoulders, the flanks flattened. The siphuncle is ventrally subcentral...
  
  . Range as for family.
• Pseudaganides Nautiliconic; whorl section subrectangular to compressed with flattened flanks converging toward a flattened to rounded venter; suture with ventral lobe and broad deep lateral lobes; siphuncle central to subcentral.. Found in the Jurassic of Europe and Pakistan.
• Xenocheilus Like Pseudonautilus but with subangular ventral shoulders and rounded, rather than pointed, lateral lobes. From the Upper Jurassic and Lower Cretaceous of Europe and north Aftrica.