''Ankyloceras'' is a genus of Early

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

cephalopods included in the oncocerid family Karoceratidae. The type species, ''Ankyloceras nesnayamiense'' named by Zhuravleva, 1974, comes from Nova Zemlya in Russia. Other species have been found in Japan, Morocco, and Russia.

Morphology

The shell of ''Ankyloceras'' is cyrtoconic, exogastrically curved with a compressed to slightly depressed elliptical cross section more narrowly rounded ventrally than dorsally. Sutures form broad lateral lobes. The Siphuncle is marginal to the convex (ventral) side of shell. Septal necks in the type species are loxochoanitic, (inwardly slanting to the siphuncle) on marginal side, short recumbent on side facing interior. Connecting rings are expanded ventrally at the adapical end of each segment and dorsally at the adoral end.

Similar and related genera

''Ankyloceras'' is similar in overall form to the earlier ''

Osbornoceras ''Osbornoceras'' is a genus of Lower Silurian cyrtoconic nautiloid cephalopods known from Ohio and possibly Manitoba, one of five general currently included in the oncocerid family Karoceratidae. Diagnosis -morphology ''Osbornoceras'' grew to b ...

'' from North America, except for the details of the siphuncle. Similar too are the oncoceratid '' Diagenoceras'' and '' Dunleithoceras'', among others, from the latter part of the Ordovician.

References

* Bjorn Kroger, 2008. Nautiloides before and during the Origin of Ammonoids in a Siruro-Devonian Section of the Tafo;at. Amto-atlas, Morocco. Special Paper in Palaeontology No. 79. The Palaeontological Association, London.
''Ankyloceas''
Paleobiology db * Sepkoski, J.J. Jr. 2002. A compendium of fossil marine animal genera. D.J. Jablonski & M.L. Foote (eds.). ''Bulletins of American Paleontology'' 363: 1–560
Sepkoski's Online Genus Database (Cephalopoda)
: See also

List of prehistoric nautiloid genera This list of nautiloids is a comprehensive listing of all genera that have ever been included in the subclass Nautiloidea, excluding purely vernacular terms. The list includes all commonly accepted genera, but also genera that are now considered i ...

Prehistoric nautiloid genera {{paleo-Nautiloidea-stub