''Trigonoceras'' is an extinct genus of prehistoric

nautiloid Nautiloids are a group of cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and species rich, with over 2,500 recorded species. Th ...

s from the nautilid family Trigonoceratidae that lived during the Early

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

in what is now western Europe. ''Trigonoceras'' has a very loosely coiled gyroconic or cyrtoconic shell with a subtriangular cross section, as indicated by fragmentary specimens. The venter on the outer rim or convex side is broad and transversely concave with angular shoulders; the sides which converge on a narrow dorsum are broadly convex. The

siphuncle The siphuncle is a strand of biological tissue, tissue passing longitudinally through the mollusc shell, shell of a cephalopod mollusc. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the li ...

is slightly dorsal of the center and is orthochoanitic.(,B.1964.) A member of the Trigonoceratidae, ''Trigonoceras'' is also a component of the superfamily Trigonocerataceae

References

* ,B.1964. Nautiloidea-Nautilida ''in the''

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology,'' published from 1953–2007 by the Geological Society of America and the University of Kansas, then 2009–present by the University of Kansas Paleontological Institute, is a definitive multi-authore ...

Part K; Geological Society of America and University of Kansas Press
(Cephalopda)
-Sepkoski's Online Genus Database Prehistoric nautiloid genera {{paleo-Nautiloidea-stub