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Oncoceratida
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 thin and siphuncle segments are variably expanded (Flower, 1950). 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 (Sweet, 1964). Physical characteristics The shells of oncocerids are primarily somewhat compressed cyrtoconic brevicones. More advanced forms include gyrocones, serpenticones, torticones, and elongate orthocones and cyrtocones, reflective of the different families and genera (Flower, 1950; Sweet, 1964). The siphuncle in the Oncocerida is commonly located at or near the ventral margin. Connecting rings are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oncoceratidae
Oncoceratidae is a family of nauatiloid cephalopods in the order Oncocerida established by Hyatt, 1884, that range from the Middle Ordovician to the Upper Silurian. Diagnosis Oncoceratidae are characterized by generally compressed, cyrtoconic, and breviconic shells with an exogastric curvature such that the ventral profile is convex or more so than dorsal, and in which the siphuncle is generally empty and located ventral of the center. In primitive forms, the siphuncle in early growth stages is composed of tubular segments with almost straight suborthochoanitic septal necks, but becomes cyrtochoanitic with expanded segments in the later growth stages, and is expanded and cyrtochoanitic throughout in advanced forms. In a few advanced forms, the siphuncle is actinosiphonate. (Flower 1950, Sweet 1964) Evolution The Oncoceratidae first appeared early in the Middle Ordovician (Sweet 1964) simultaneously with the Graciloceratidae, Tripteroceratidae, and Valcouroceratidae, deri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 thin and siphuncle segments are variably expanded (Flower, 1950). 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 (Sweet, 1964). Physical characteristics The shells of oncocerids are primarily somewhat compressed cyrtoconic brevicones. More advanced forms include gyrocones, serpenticones, torticones, and elongate orthocones and cyrtocones, reflective of the different families and genera (Flower, 1950; Sweet, 1964). The siphuncle in the Oncocerida is commonly located at or near the ventral margin. Connecting rings are mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nautiloids
Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded species. They flourished during the early Paleozoic era, when they constituted the main predatory animals. Early in their evolution, nautiloids developed an extraordinary diversity of shell shapes, including coiled morphologies and giant straight-shelled forms ( orthocones). Only a handful of rare coiled species, the nautiluses, survive to the present day. In a broad sense, "nautiloid" refers to a major cephalopod subclass or collection of subclasses (Nautiloidea ''sensu lato''). Nautiloids are typically considered one of three main groups of cephalopods, along with the extinct ammonoids (ammonites) and living coleoids (such as squid, octopus, and kin). While ammonoids and coleoids are monophyletic clades with exclusive ancestor-descendant rela ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Graciloceratidae
The Graciloceratidae is a family of nautiloid cephalopods from the Middle and Upper Ordovician belonging to the Oncocerida, characterized by exogastric cyrtocones that expand slightly or moderately and have thin walled, orthochoanitic marginal or subventral, tubular siphuncles (Sweet 1964). The Graciloceratidae was proposed by Rousseau Flower in 1950 and at that time placed in the Basslerocerida which has since been abandoned. It is now assigned to the Oncocerida (Sweet 1964). Phylogeny The Graciloceratidae are most likely derived from the Bassleroceratidae (Flower 1950) from which they differ primarily in having thin rather than thick connecting rings. They are also the most likely source for the Oncoceratidae, Tripteroceratidae, and Valcouroceratidae (Flower 1950). Included genera The Graciloceratidae contains five known genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Poterioceratidae
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 (curved upwardly so as the lower side, the venter, is convex viewed from the side) 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. The origin of the Poterioceratidae is undetermined but may have their origin in some Silurian member of the Acleistoceratidae or perhaps even in some Ordovician oncoceratid through an unknown Siluri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Brevicoceratidae
The Brevicoceratidae is a family of oncocerids that contains genera characterized by exogastric (or rarely endogastric) 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 The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ... to the Upper Devonian. Brevicoceratidae is named for the Middle Devonian genus, '' Brevicoceras'', from North America. All told there are some 17 named genera. The family begins with '' Oxygonioceras'' in the Middle Silurian, sole recognized representative of that time, and reaches its greatest diversity with 12 genera in the Middle Devonian. The Brevicoceratidae are reduced to fou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acleistoceratidae
The Acleistoceratidae is a family of oncocerids that contains genera characterized by depressed (or rarely compressed) exogastric brevicones and cyrtocones (Sweet, 1964 K398) that range from the Middle Silurian to the Middle Devonian. The siphuncle is broadly expanded, and in some actinosiphonate. The Acleistoceratidae are derived from '' Oncoceras'' (Oncoceratidae) through '' Amphycertoceras'', independently of the ''Oonoceras'' stock. The family is named for the genus ''Acleistoceras ''Acleistoceras'' is a genus of the oncocerid, nautiloid Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and '' Allonautilus''. Fossil nautiloi ...''. All told some 22 genera have been described. References * Flower,R.H. 1950; Flower & Kümmel; A Classification of the Nautiloidea; Journal of Paleontology, Vol 24, no 5, pp604–610, Sept 1950 * Sweet, W.C. 1964; Nautiloidea-Oncocerida, in the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hemiphragmoceratidae
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. (Sweet 1964, Flower 1950). Shells are compressed with the apical portion curved and the anterior straight. Siphucles are nummuloideal with expanded spheroidal segments and continuously actinosiphonate interiors. The Hemiphragmoceratidae are probably descended from the Oncoceratidae and are known from the middle and upper Silurian but may range into the middle 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 ... (Sweet 1964). They are similar with regards to their constricted and ornate apertures to the middle Silurian exogastric Trime ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nothoceratidae
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. Genera *'' Blakeoceras'' *'' Bolloceras'' *'' Conostichoceras'' *'' Cyrthoceratites'' *'' Lorieroceras'' *'' Metaphragmoceras'' *'' Mutoblakeoceras'' *'' Nothoceras'' *'' Paraconradoceras'' *'' Perimecoceras'' *'' Tafilaltoceras'' *'' Turnoceras'' References * Sweet, W. C. 1964; Nautiloidea -Oncocerida; Treatise on Invertebrate Paleontology The ''Treatise ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tripteroceratidae
The Tripteroceratidae is a family of depressed, straight to slightly curved nautiloid cephalopods from the middle and upper Ordovician with generally flattened venters and empty siphuncles with straight to inflated segments included in the Oncocerida (Sweet, 1964). The Tripteroceratidae appeared almost simultaneously with the Oncoceratidae and Valcouroceratidae early in the Middle Ordovician, and are most likely derived from the Graciloceratidae The Graciloceratidae is a family of nautiloid cephalopods from the Middle and Upper Ordovician belonging to the Oncocerida, characterized by exogastric cyrtocones that expand slightly or moderately and have thin walled, orthochoanitic marginal .... Genera The Tripteroceratdae includes five known genera, as briefly described. ''Tripteroceras'', the type genus, named by Hyatt (1884) is characterized by a small, straight or slightly exogastric shell with a broad, depressed triangular cross section. The venter, underneath, is flat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ordovician
The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The Ordovician, named after the Celtic Britons, Welsh tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same Rock (geology), rock beds in North Wales in the Cambrian and Silurian systems, respectively. Lapworth recognized that the fossil fauna in the disputed Stratum, strata were different from those of either the Cambrian or the Silurian systems, and placed them in a system of their own. The Ordovician received international approval in 1960 (forty years after Lapworth's death), when it was adopted as an official period of the Paleozoic Era by the International Union of Geological Sciences, Intern ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
