Nostoceratidae

Nostoceratidae
Nostoceras sp
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	Ammonoidea
Order:	Ammonitida
Suborder:	Ancyloceratina Wiedmann, 1966
Superfamily:	Turrilitaceae
Family:	Nostoceratidae
Genera
Nostoceras (type genus) Madagascarites (Ryuella) Nipponites Bostrychoceras Eubostrychoceras Muramotoceras Ainoceras (Jouainoceras) Anaklinoceras Cirroceras Solenoceras Hyphantoceras Spiroxybeloceras Pravitoceras ?Didymoceras ?Yezoceras

Family Nostoceratidae was a diverse group of heteromorph ammonites found throughout the oceans of the world during the Late Cretaceous. The nostoceratids are famous for the bizarre coiling of their shells. Many genera, such as Yezoceras, Ainoceras, Anaklinoceras, and some species of Bostrychoceras and Eubostrychoceras, display, as young shells at least, a helical coiling very similar to the shells of the related family, Turrilitidae. As adults, though, the coils then curve away from the axis of coiling, either as an oxbow-like curve around the juvenile coils as in Ainoceras and Anaklinoceras, or in a simple curved loop beneath the juvenile coils, as in Yezoceras. Other genera form loose coils, sometimes in a spiral, such as those of Madagacarites (Ryuella), Muramotoceras, Hyphantoceras, and the infamous Nipponites.

The ecology of nostoceratids is the subject of continued speculation, as the bizarrely coiled shells have no streamlining, strongly suggesting that the living animals had extraordinarily poor swimming ability, if any ability at all. As such, experts and ammonite enthusiasts presume that the nostoceratids either floated passively in the water column, or were bottom-dwellers that may or may not have crawled on the seafloor.

The nostoceratids, as with all other Cretaceous ammonites, perished during the Cretaceous–Tertiary extinction event.

See also

• Nautiloid
• Lituites
• Orthoceras

External links

• Scientific report on the functional morphology of Cretaceous heteromorph ammonites