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Cyrtogomphoceratidae
The Cyrtogomphoceratidae are a family in the cephalopod order Discosorida that comprises genera commonly with compressed, endogastrically curved shells. Siphuncles lie close to the ventral side, segments are broadly inflated, connecting rings thick and apically expanded thick bullettes. Chambers are short, separated by shallow, dish shaped septa. Apertures are generally simple. The Cyrtogomphoceratidae are derived from the discosorid family Reudemannoceratidae, probably from '' Reudemannoceras'', through the ancestral genus '' Ulrichoceras'', and have a range from the Middle Ordovician to the Lower Silurian. The familyTeicher, C. 1964. Nautiloidea-Discosorida. Treatise on Invertebrate Paleontology, Part K. Teichert and Moore, eds. includes: :*'' Cyrtogomphoceras'' :*'' Kiaeroceras'' :*'' Konglungenoceras'' :*'' Landeroceras'' :*'' Parryoceras'' :*'' Strandoceras'' :*'' Ulrichoceras'' ''Ulrichoceras'' is also considered the source for the exogastric Westonoceratidae. T ... [...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, Ne ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ulrichoceras
''Ulrichoceras'' is recognised as the basal cyrtogomphoceratid genus, which is the source for the rest of the Cyrtogomphoceratidae as well as for the Westonoceratidae. The Cyrtogomphoceratidae are endogastric, the Westonoceratidae, exogastric. ''Ulrichoceras'' has a cyrtoconic, endogastric shell that expands fairly rapidly to the middle of the body chamber, then contracts toward the aperture. The cross section is slightly depressed, atypical for cyrtogomphoceratids but not so for Reudemannoceratids; dorsal and ventro lateral sides are broadly rounded, the venter moderately flattened. Sutures have broad ventral lobes. The siphuncle is between the center and the venter; segments are short and not strongly contracted at the septal foremina, connecting rings are thickened and have enlarged bullettes. ''Ulrichoceras'', named by Foerste, 1925, type ''U. beloitense'', comes from the Middle Ordovician of Wisconsin, U.S.A. It is intermediary in form between '' Reudemanoceras'' and the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Konglungenoceras
''Konglungenoceras'' is a discorid from the lower Silurian of Europe (Norway) included in the Cyrtogomphoceratidae that lacks the septal foramina grasping bullettes at the adapical end of the connecting rings. shells are endogastric and strongly compressed, such that the ventral or siphuncle side is curved inward and the dorso-ventral height is greater than the width. Endosiphuncular deposits in the apical portion of the siphuncle consist of thick overlapping parietal laminae that form endocones, similar to those is ''Discosorus'' and '' Alpenoceras''. Although included in the Cyrtogomphoceratidae, derivation undetermined, siphuncle characters as well as stratigraphic position are suggestive of the Discosoridae Discosoridae comprise a family of endogastric discosorids, (Cephalopoda, Nautiloidea), with endocones in the siphuncle, ranging from the Middle Silurian to Middle Devonian. Shell morphology The shell in the Discosoridae is conical, expanding va .... References *Curt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strandoceras
''Strandoceras'' is a strongly curved cyrtogomphoceratid with a laterally compressed cross section from the middle and upper Ordovician of Northern Europe; Estonia, Norway, the U.K. The body chamber of ''Stradoceras'' is straighter and more slender than the chambered phragmocone; the venter narrowly rounded with a shallow hyponomic sinus; the aperture open, sutures with shallow lateral lobes. The siphuncle is close to the venter which is on the inside, endogastric curvature. Segments are large and broadly rounded; connecting rings thick, bullettes large. ''Strandoceras'' gave rise to the Phragmoceratidae and very likely to '' Kiaeroceras'' and '' Cyrtogomphoceras'', which in turn gave rise to '' Landeroceras'', within the Cyrtogomphoceratidae The Cyrtogomphoceratidae are a family in the cephalopod order Discosorida that comprises genera commonly with compressed, endogastrically curved shells. Siphuncles lie close to the ventral side, segments are broadly inflated, connecti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reudemannoceratidae
The Reudemannoceratidae are the ancestral and most primitive of the Discosorida, an order of cephalopods from the early Paleozoic. The Reudemannoceratidae produced generally medium-sized endogastric and almost straight shells with the siphuncle slightly ventral from the center. Derivation The Reudemannoceratidae first appeared at the beginning of the Middle Ordovician, North American Whiterock stage, (since replaced by the ICS Dapingian), and are restricted to the lower part of that series. (the middle Ordovician). Their origin is unknown. The siphuncles in early members contain features in the early growth stages reminiscent of the siphuncular bulbs found the archaic Plectronoceratae of the Late Cambrian. (Flower and Teichert 1957) but so far no unambiguous Lower Ordovician intermediaries have been found. Characters Reudemannoceratids are characterized by having short septal necks in the juvenile portion of the siphuncle, toward the apex of the shell, which later in life grow ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kiaeroceras
''Kiaeroceras'' is a slender, nearly stright shelled, cyrogomphoceratid ( Nautiloidea-Discosorida) from the Upper Ordovician of northern Europe (e.g. Norway). The cross section of the shell is compressed, height greater than width. The body chamber is slightly contracted so as to narrow toward the aperture, which in some is slightly flared. The venter, narrowly rounded. The siphuncle is close to the venter, septal necks short, connecting rings thick, bullettes prominent. ''Kiaeroceras'' is thought to be derived from ''Strandoceras ''Strandoceras'' is a strongly curved cyrtogomphoceratid with a laterally compressed cross section from the middle and upper Ordovician of Northern Europe; Estonia, Norway, the U.K. The body chamber of ''Stradoceras'' is straighter and more sle ...'' although derivation is possibly from '' Cyrtogomphoceras'', which is intermediary in form. References *Flower, Rousseau H. and Curt Teichert, 1957; The Cephalopod Order Discosorida, in University of K ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Landeroceras
''Landeroceras'' is a genus of straight shelled cyrtogomphoceratid from the Middle Ordovician Big Horn dolomite of Wyoming. The shell of ''Landeroceras'' is a subcylindrical brevicone with the siphuncle on one side, determined as ventral. Siphuncle segments are short and well expanded into the chambers. Connecting rings are thick, septal necks cyrochoanitic to recumbent, bullettes markedly swollen. ''Landeroceras'' is at the end of a small offshoot within the discosorid family Cyrtogomphoceratidae that also includes ''Cyrtogomphoceras'', and not in the line which gave rise to the Phragmoceratidae The Phragmoceratidae is a family of extinct nautiloid cephalopods from the Order Discosorida that lived during the latter part of the Silurian. Diagnosis Phragmoceratids are characterized by generally compressed, upwardly curved endogastric sh .... References * Flower, R H and Teichert, C., 1957. The Cephalopod Order Discosorida. University of Kansas Paleontological Contributio ... [...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 ''Winnipegocera ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phragmoceratidae
The Phragmoceratidae is a family of extinct nautiloid cephalopods from the Order Discosorida that lived during the latter part of the Silurian. Diagnosis Phragmoceratids are characterized by generally compressed, upwardly curved endogastric shells with slit-like apertures for egress and ventral siphuncles with broadly expanded segments, thick connecting rings, and small to vestigial bullettes. Phragmoceratids are morphologically similar in regards to their constricted apertures to the more cylindrical and orthoconic Mandaloceratidae, also discosorids, and to the oncocerid 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. (S ... (Sweet 1964); both which also come from the Silurian. Derivation The Phragmoceratidae are derived from the Ordovician Cyrtogomphocerat ... [...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] |
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 Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out. One important event in this period was the initial establishment of terrestrial life in what is known as the Silurian-Devonian Terrestrial Revolution: vascular plants emerged from more primitive land plants, dikaryan fungi started expanding and diversifying along with glomeromycotan fungi, and three groups of arthropods (myriapods, arachnids and hexapods) became fully terrestrialized. A significant evolutionary milestone during ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyrtogomphoceras
''Cyrtogomphoceras'' is a genus of nautiloid cephalopods, recognized by its large breviconic shell with a notable endogastric curvature. The shell is fusiform in profile, reaching maximum width at or near the base of body chamber, which narrows toward the aperture. The siphuncle is large and slightly removed from the ventral side, that with the concave longitudinal profile. Siphuncle segments are short, as are chambers; septal necks recurved, connecting rings thick, bullettes at the apical end of the rings swollen. Cameral deposits are lacking. ''Cyrtogomphoceras'' seems to be derived from ''Strandoceras'' by a reduction in the degree of endogastric curvature and may have given rise to '' Landeroceras'' by a further evolutionary straightening of the shell. ''Cyrtogomphoceras'', named by Foeste, 1924, has been found in middle and upper Ordovician beds in North America and Greenland. Fossils identified as such have also been found in the Silurian of Estonia. The type species is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
