Ainoceras

Ainoceras Temporal range: Campanian[1] PreЄ Є O S D C P T J K Pg N
Ainoceras kamuy
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	Ammonoidea
Order:	Ammonitida
Suborder:	Ancyloceratina Wiedmann, 1966
Superfamily:	Turrilitaceae
Family:	Nostoceratidae
Genus:	Ainoceras

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Ainoceras ("Ainu's Horn") is a genus of extinct, aberrantly coiled ammonite cephalopod that live in the Pacific Ocean during the Campanian division of the Cretaceous, where Japan is today. Their shells were coiled very similarly to the related Anaklinoceras, in that, when young, the shell coiled helically, and then upon reaching adulthood, the shell then bent over the older coils. However, Ainoceras differed in this respect in that, whereas in Anaklinoceras, the youngest coil wrapped very closely around the older coils, while in Ainoceras, the youngest coil bent over the older coils in a wide loop or oxbow.

References

Notable fossil cephalopods (listed by first occurrence)
Cenozoic	The belemnite-cuttlefish-like Belosaepia	Evolutionary history of cephalopods
Mesozoic	Advanced nautiloids Nautilaceae True ammonites Early coleoids Proteroctopus Styletoctopus Keuppia Palaeoctopus Paleocirroteuthis Ceratitid ammonoids late Nautilida Advanced belemnoids Diplobelids: Diplobelus Belemnites: Belemnites Belemnopsis Belemnotheutis
Palaeozoic	First appearance of long-lasting lineages Goniatite and ceratite ammonoids Probable coleoid ancestor Bactritida Earliest belemnoids: Aulacocerids: Aulacoceras Phragmoteuthids: Phragmoteuthis Early forms the earliest cephalopod group Ellesmerocerida Orthocones: Endocerida, Orthocerida, Actinocerida Brevicones: Ascocerida, Oncocerida Earliest coiled cephalopods: Tarphycerida Spirulid?: Shimanskya Octopus Pohlsepia
Cambrian	Earliest unambiguous cephalopods: Plectronocerida Plectronoceras Monoplacophoran-like ancestral forms: Knightoconus Possible, nude, "stem-group cephalopods": Nectocarididae