''Brevicoceras'' is an extinct

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 ...

genus from the order

Oncocerida The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian (early Carboniferous; one possible member is known from the Early Permian), in which the connecting rings are t ...

Flower, R.H & Kummel, B 1950, A Classification of the Nautiloidea, Journal of Paleontology 24(3) Sept 1950 with wide distribution in the Middle

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

in Eastern North America, Russia and Morocco.Kroger, B. 2008. Nautiloids Before and During the Origin of Ammonoids. Special Papers in Palaeontology 79, The Palaeontological Association, London. Nautiloids form a broad group of shelled

cephalopods A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

that were once diverse and numerous but are now represented by only a handful of species in two

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

Taxonomy

Brevicoceras was named by Flower in 1938.Sweet, W. C. 1964. Nautiloidea -Oncocerida.

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, Teichert & Moore (eds) and is the

type genus In biological taxonomy, the type genus (''genus typica'') is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearin ...

for the Brevicoceratidae.

Morphology

''Brevicoceras'' produced short, breviconic, shells in which the ventral side of the

phragmocone The phragmocone is the chambered portion of the shell of a cephalopod. It is divided by septa into camerae. In most nautiloids and ammonoids, the phragmocone is a long, straight, curved, or coiled structure, in which the camerae are linked by ...

, or chambered part, is longitudinally convex in profile and the opposite dorsal side concave, resulting in their being exograstric - i.e. upwardly curved. The shell reaches its maximum width near the front of the phragmocone or rear of the living chamber. From there it narrows somewhat toward the transverse and slightly contracted

aperture In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...

In section the shell is slightly broader that high. The dorsal side is also somewhat flattened while the ventral or siphuncular side is more narrowly rounded. Septa are shallow and evenly curved; sutures are with broad shallow dorsal and ventral lobes that diverge to the rear and lateral saddles that diverge forward. 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 ...

located close to the ventral margin is slender with short expanded segments that give it a nummuloidal or beaded appearance, and contains irregular blade-like actinosiphonate deposits. The aperture has a pair a ventro-lateral salients, or projections, and a narrow mid ventral hyponomic sinus confirming the siphuncle is ventral.

References

* 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 -CEPHALOPODA
{{Taxonbar, from=Q16975295 Oncocerida Paleozoic life of Ontario