Related Research Articles
The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian, in which the connecting rings are thin and siphuncle segments are variably expanded. At present the order consists of some 16 families, a few of which, such as the Oncoceratidae, Brevicoceratidae, and Acleistoceratidae contain a fair number of genera each while others like the Trimeroceratidae and Archiacoceratidae are represented by only two or three.
The Brevicoceratidae is a family of oncocerids that contains genera characterized by exogastric gyrocones, brevicones, and torticones. that tend to develop vestigial actinosiphonate deposits and subtriangular transverse sections. The Brevicoceratidae are derived from Oonoceras (Oncoceratidae) and range from the mid-Silurian to the Upper Devonian.
Turnoceras is a genus of Devonian cephalopods belonging to the oncocerid family Nothoceratidae. Its shell is broadly expanding and exogastrically curved such that the flattened dorsum is on longitudinally concave side. Aperture unconstricted with no hyponomic sinus for the water jet funnel. siphuncle along the outer, ventral, side, with radial, plate-like actinosiphonate deposits occupying the interior.
Octamerella is an extinct genus of prehistoric nautiloids from the oncocerid family Hemiphragmoceratidae that lived in what is now Europe and North America during the Middle Silurian.
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.
Brevicoceras is an extinct nautiloid genus from the order Oncocerida with wide distribution in the Middle Devonian in Eastern North America, Russia and Morocco. Nautiloids form a broad group of shelled cephalopods that were once diverse and numerous but are now represented by only a handful of species in two genera.
Streptoceras is a genus in the extinct oncocerid family Acleistoceratidae that plied the shallow sea floor from the Middle Silurian to the Middle Devonian. Streptoceras is characterized by a shell that is large but short in proportion (breviconic) with the ventral profile convex and dorsal profile concave in the posterior part, convex over the body chamber, then concave toward the front, like Amphycertoceras, but with a triangular shaped aperture. Streptoceras is found in the Middle Silurian of North America, in Ontario.
Acleistoceras is a genus of the oncocerid, nautiloid family Acleistoceratidae that lived in the shallow seas that covered much of North America during the Devonian; living from 409—383.7 mya, existing for approximately 25.3 million years.
Hemiphragmoceratidae is a family of endogastrically brevconic oncocerids characterized by elaborately visored apertures in which the hyponomic sinus in mature specimens is on a spout-like process and there may be lateral and dorsal salients.. Shells are compressed with the apical portion curved and the anterior straight. Siphucles are nummuloideal with expanded spheroidal segments and continuously actinosiphonate interiors.
The Phragmoceratidae is a family of extinct nautiloid cephalopods from the Order Discosorida that lived during the latter part of the Silurian.
Conostichoceras is a genus of exogastric, breviconic oncocerids included in the family Nothoceratidae, known from the Middle Devonian of central Europe and Upper Devonian of Australia. It probably lived on and swum above the sea floor.
Stereotoceras is a Middle and Upper Devonian genus in the oncocerid family Brevicoceratidae that formed a smooth, depressed, gyroconic shell with the dorsum much flatter that the venter. Sutures are straight ventrally but have dorsal lobes. Growth lines outline a ventral hyponomic sinus but are otherwise transverse. The siphuncle in ventral, nummuloidal, with discrete, irregular, actinosiphonate deposits at the septal foramina.
Pentameroceras is a straight to slightly exogastric breviconic oncocerid from the middle Silurian of North America and Europe belonging to the Trimeroceratidae.
Nothoceratidae is a family of nautiloid cephalopods in the orthoceratoid order Oncocerida in which shells are exogastrically or endogastrically breviconic, planospiral, or torticonic; often with a constricted or visored aperture; and a siphuncle commonly composed of concave segments and occupied by actinosiphonate deposits. Some ten genera have been described which lived during the time between the Early Silurian and Late Devonian. The ancestral form is probably Perimecoceras which is known from the Upper Silurian of central Europe and which is similar in external form the Oonoceras from the Oncoceratidae.
Poterioceratidae is a family of nautiloid cephalopods included in the Oncocerida that lived during the period from the Early Devonian to the Early Carboniferous (Mississippian). Members of the Poterioceratidae are distinguished by a subcircular to compressed exogastric shell that has no hyponomic sinus and a central to subcentral siphuncle composed of subquadrate to nummuloidal segments in which the septal necks are more strongly curved on the upper, or dorsal side. This is opposite from the Karoceratidae in which siphuncle segments are inflated ventrally but straight dorsally. Some poterioceratid genera have actinosiphonate structures or annular deposits within the siphuncle. In others it is empty.
Grimsbyoceras is a nautiloid genus included in the Oncocerida order of the family Acleistoceratidae that lived during the Middle Devonian. They have been found in North America (Illinois) and central Europe.
Gomphoceras is a questionable nautiloid cephalopod genus assigned to the Oncocerida. The family to which it might belong is undetermined.
Tetrameroceras is a genus of short, essentially straight, breviconic, nautiloid cephalopods from the middle and Upper Silurian of Europe and North America included in the oncocerid family Hemiphragmoceraidae.
Hexameroceras is a genus of nautiloid cephalopods belonging to the order Oncocerida that lived during the middle and late Silurian. Its fossils have been found in North America in Indiana, New York, Ohio, and Wisconsin, and in Europe in the Czech Republic.
Hipparionoceras is a genus of oncocerids from the middle Devonian of Europe, North America, and China that lived around 395 million years ago.
References
 | This article includes a list of references, related reading, or external links, but its sources remain unclear because it lacks inline citations .(January 2015) |
- W.C. Sweet 1964. Nautiloidea - Oncocerida, Treatise on Invertebrate Paleontology, Part C. University of Kansas Press, Lawrence, Ka.
- Aletoceras in Fossilworks, 1/5/15
 | This prehistoric nautiloid-related article is a stub. You can help Wikipedia by expanding it. |