Nostoceratidae is a diverse

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

heteromorph The Ancyloceratina were a diverse suborder of ammonite most closely related to the ammonites of order Lytoceratina. They evolved during the Late Jurassic but were not very common until the Cretaceous period, when they rapidly diversified and bec ...

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

s found throughout the oceans of the world during the Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

. The nostoceratids are famous for the bizarre coiling of their shells. Many genera, such as '' Yezoceras'', '' Ainoceras'', '' Anaklinoceras'', and some species of ''

Bostrychoceras ''Bostrychoceras'' is a genus of heteromorph ammonite from the family Nostoceratidae. Fossils have been found in Late Cretaceous sediments in Europe and North America North America is a continent in the Northern Hemisphere and alm ...

'' and ''

Eubostrychoceras ''Eubostrychoceras'' is a genus of helically wound, corkscrew form, heteromorph ammonite which lived during the Upper Cretaceous (M Turonian - Campanian). The genus is included in the ancycleratid family Nostoceratidae. The shell of ''Eubostryc ...

'', 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 __NOTOC__ An oxbow is a U-shaped metal pole (or larger wooden frame) that fits the underside and the sides of the neck of an ox or wikt:bullock, bullock. A bow pin holds it in place. The term "oxbow lake, oxbow" is widely used to refer to a U-sh ...

-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 '' Madagascarites'', ''

Muramotoceras ''Muramotoceras'' was an unusual genus of heteromorphic ammonite. It was known only from Japan until researchers reported in 2001 that the genus was present in Alaska's Matanuska Formation as well. Its remains likely date to the middle Turonian ...

'', '' Hyphantoceras'', and the infamously convolute ''

Nipponites ''Nipponites'' is an extinct genus of heteromorph ammonites. The shells of ''Nipponites'' (primarily ''N. mirabilis'') form "ox-bow" bends, resulting in some of the most bizarre shapes seen among ammonites. The ecology of ''Nipponites'', as wit ...

''. 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–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the ...

References

External links

Scientific report on the functional morphology of Cretaceous heteromorph ammonites
Ammonitida families Cretaceous ammonites Turrilitoidea Late Cretaceous first appearances Maastrichtian extinctions {{Ammonitida-stub