''Acanthonautilus'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus in the nautilid family Solenochildae (Aipocerataceae) from the Upper Mississippian of North America and equivalent (uL Carb) strata in Europe, first described by Foord in 1896. ''Acanthonautilus'', like ''

Solenochilus ''Solenochilus'', type genus of the Solenochilidae is an extinct cosmopotilian nautilid from the Lower Pennsylvanian to the Lower Permian with a rapidly expanding, coiled globular shell with few whorls, from which prominent spines extend latera ...

'', has an involute, globular shell of few volutions that enlargens with fair rapidity, with prominent lateral spines extending from the umbilical area at maturity. The

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 ...

in ''Acanthonautilus'' is narrower than in ''Solenochilu''s and not as sinuous. As with ''Solenochilus'', septal necks on the outer, or ventral, side are straight, but those on the inner, or dosal, side rather than being recumbent are simply curved, cyrtochoanitic. Most of the siphuncle is thin connecting ring which from the outside is slightly ventrally concave and slightly dorsally convex between septa. ''Acanthonautilus'' may have been derived from ''Aipoceras'', or possibly ''Asymptoceras'' and give rise, principally through modification of the siphuncle, to ''

''.

References

* Kummel 1964; Nautiloidea-Nautilida,

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology'' (or ''TIP'') published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and co ...

, Part K Nautiliodea, Geological Society of America and University of Kansas press. * 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)
Prehistoric nautiloid genera {{paleo-nautiloid-stub