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Simardoceras
''Simardoceras'' is a genus in the discosorid (nautiloid cephalopod) family Westonoceratidae from the Middle Ordovician of Quebec. The shell of ''Simardoceras'' is a moderately expanding exogastric cyrtocone, said to resemble a rather large ''Oncoceras'', but with a siphuncle that is definitely discosorid. The venter is almost uniformly convex in longitudinal profile. The dorsal profile changes from concave in the apical portion to straight, then slightly convex at the front of the phragmocone and back of the body chamber, the concave again near the aperture. The siphuncle is ventral. Segments are subquadrate in outline and are longer than broad. Connecting rings are thick. Although ''Simardoceras'' somewhat resembles ''Winnipegoceras'' is the form of its siphuncle, it differs in its very broad cross section. The slender siphuncle segments also distinguish it from the apparently more closely related ''Sinclairoceras'' and from its apparent derivative ''Reedsoceras ''Reedsocera ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sinclairoceras
''Sinclairoceras'' is a nautiloid cephalopod in the discosorid family Westonoceratidae from the Middle Ordovician Simard Limestone of Quebec Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirtee .... The shell is laterally compressed, upwardly curved, and short; an exogastric brevicone with the venter narrowly and dorsum broadly rounded. The dorsum, at the upper surface, is only slightly concave longitudinally. The venter, at the lower surface, is more strongly convex longitudinally, drawing away from the dorsum and forming a hump at the anterior end of the phragmocone where ''Sinclairoceras'' reaches its greatest width. The upper and lower sides of the body chamber are essentially straight and virtually parallel, flaring slightly at the aperture. The sides however converge on the ape ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Westonoceratidae
Westonoceratidae are exogastric, mostly compressed, Discosorida of moderate size from the Middle Ordovician to the Lower Silurian. The siphuncle is typically close to the convexly curved outer margin of the phragmocone – the chambered part of the shell – taken to be ventral but may be more central in some genera. Connecting rings are thin to moderately thick with inflated bullettes grasping the previous septal foremina. Parietal deposits within the siphuncle from endocones in advanced genera and cameral deposits are found in some. The Westonoceratidae are derived from the Cyrtogomphoceratidae through the cyrtogomphoceratid, '' Ulrichoceras''. In turn, the Westonoceratidae gave rise to a small group of discosorids, the Lowoceratidae, which form an intermediary step before the Discosoridae. Two principal lineages have been identified, both stemming from the genus '' Teichertoceras'', a derivative of ''Ulrichoceras''. One goes simply from '' Westonoceras'' to '' Winnipeg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reedsoceras
''Reedsoceras'' is a genus of large discosorids (Nautiloidea) in the family Westonoceratidae from the middle and upper Ordovician of North America. ''Reedsoceras'' was named as a genus characterized by rapidly expanding exogastric cyrtocones with unconstricted apertures and straight sutures. The siphuncle is close to the venter, which is the externally convex side of the shell, and is composed of very short, broadly rounded segments. Structure of the siphuncle wall is unknown. ''Reedsoceras'' seems to be derived from '' Simardoceras'' and to be more closely related to a group that also includes ''Sinclairoceras'' than to other westonoceratids, especially those with long narrowing body chambers and bent back exogastric phragmocones like ''Winnipegoceras ''Winnipegoceras'' is an extinct nautiloid genus from the Ordovician belonging to the Order Discosorida. Phylogeny ''Winnipegoceras'' is included in the discosorid family Westonoceratidae and is derived from '' Westonoceras ... [...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] |
Discosorida
Discosorida are an order of cephalopods that lived from the beginning of the Middle Ordovician, through the Silurian, and into the Devonian. Discosorids are unique in the structure and formation of the siphuncle, the tube that runs through and connects the camerae (chambers) in cephalopods, which unlike those in other orders is zoned longitudinally along the segments rather than laterally. Siphuncle structure indicated that the Discosorida evolved directly from the Plectronoceratida rather than through the more developed Ellesmerocerida, as did the other orders. Finally and most diagnostic, discosorids developed a reinforcing, grommet-like structure in the septal opening of the siphuncle known as the bullette, formed by a thickening of the connecting ring as it draped around the folded back septal neck. Evolution The origin of the Discosorida is unknown, thought at one timeRousseau H. Flower. 1964. The Nautiloid Order Ellesmerocerida (Cephalopods); relevant pages. Memoir 12 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oncoceras
''Oncoceras'' is a genus of oncocerids, family Oncoceratidae from the middle and upper Ordovician of North America and Europe. The shell, or conch, of ''Oncoceras'' is relatively short, a curved, compressed brevicone with a maximum width in the phragmocone just behind the body chamber, narrowing toward the aperture. 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 ... is small, necks recurved. References * Waltre C. Sweet, 1964. Nautiloidea-Oncocerida. Treatise on Invertebrate Paleontology, Part K. Geological Society of America. Prehistoric nautiloid genera Ordovician cephalopods Middle Ordovician first appearances Late Ordovician extinctions Paleozoic life of the Northwest Territories Paleozoic life of Quebec {{paleo-nautiloidea-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Winnipegoceras
''Winnipegoceras'' is an extinct nautiloid genus from the Ordovician belonging to the Order Discosorida. Phylogeny ''Winnipegoceras'' is included in the discosorid family Westonoceratidae and is derived from '' Westonoceras''. Westonoceratidae have mostly medium to large, compressed, exogastric shells with moderately sized siphuncles composed of short folded back septal necks and generally thin connecting rings with swollen bullettes and which contain internal linings. (Flower & Teichert 1957; Teichert 1964) Description ''Winnipegoceras'', named by Foerste (1922) for fossils found near Winnipeg in Manitoba, Canada, is known by it large, slender, compressed, strongly curved exogastric shells; long slender body chamber and siphuncle that is slightly removed from the venter which is the outer, longitudinally convex margin. Siphuncle segments are strongly narrowed at the septal foremina, bullettes swollen, parietal and other internal deposits rarely preserved. (ibid) See also * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ordovician Cephalopods Of North America
The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic 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 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 beds in North Wales in the Cambrian and Silurian systems, respectively. Lapworth recognized that the fossil fauna in the disputed 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 Geological Congress. Life continued to flourish during the Ordovician as it did in the earlier Cambri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prehistoric Nautiloid Genera
Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use of symbols, marks, and images appears very early among humans, but the earliest known writing systems appeared 5000 years ago. It took thousands of years for writing systems to be widely adopted, with writing spreading to almost all cultures by the 19th century. The end of prehistory therefore came at very different times in different places, and the term is less often used in discussing societies where prehistory ended relatively recently. In the early Bronze Age, Sumer in Mesopotamia, the Indus Valley Civilisation, and ancient Egypt were the first civilizations to develop their own scripts and to keep historical records, with their neighbors following. Most other civilizations reached the end of prehistory during the following Iron Age. T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
