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Discosorus
''Discosorus'', a genus of the Discosorida and member of the family Discosoridae. Not to be confused with ''Discoceras''. ''Discosorus'' consists of rapidly expanding endogastric brevicones, mostly known from isolated siphuncles composed of broadly expanded segments that increase rapidly in size. Septal necks are recumbent, connecting rings thin, bullettes small. The siphuncle interior is occupied by endocones produced by layered annular deposits expanded back toward the apex, leaving a central tube running down the middle. The short phragmocone is poorly known. ''Discosorus'' is found in the Middle Silurian of eastern and arctic North America and as part of the Discosoratidae is derived from the Lowoceratidae which forms a link in the Early Silurian from the Late Ordovician exogastric ''Faberoceras'' of the Westonoceratidae. See also *List of nautiloids References *Discosorus, pK336 in Vol K of the Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 variably with respect to genus. Curvature tends to be slight with the ventral or siphuncular side slightly concave in profile (the endogastric condition), and the opposite dorsal side arched or convex in profile (another endogastric condition). The siphuncle is composed of broadly rounded segments the increase rapidly in size toward the aperture, with growth. Expansion is commonly greater than that of the shell itself, and lies ventral of the center. Septal necks are short, brims long and recumbent. Connecting rings are thin and poorly known. Bullettes at the apical end of the connecting rings, which grasp the periphery of the previous septal foramina and connect to the inside of the previous septal necks, are never swollen. Endocones ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Discoceras
''Discoceras'' is an extinct marine cephalopod mollusk, a member of the Trocholitidae in the Tarphycerida. It is distinct from ''Discosorus'', It is characterized by closely coiled, gradually expanding shells with a subquadrate cross section, that may be ribbed or smooth. The sides are broadly rounded; the venter is wide and slightly rounded. The maximum width is slightly dorsal of the middle. The dorsum has a slight to moderate impression. The siphuncle starts off central for the first half whorl then becomes marginodorsal in the succeeding two whorls, then subdorsal at maturity. As with ''Trocholites'', the dorsal siphuncle in ''Discoceras'' probably indicates an orientation during life that places the back of the living chamber high in the shell.''Discoceras'', p K360 in Vol K of the ''Treatise on Invertebrate Paleontology'' in the section on the Trocholitidae, pp K359-K362, in the Chapter on the Tarphycerida by Furnish and Glenister starting with page K343. ''Discoceras' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lowoceratidae
The Lowoceratidae is a small family of discosorids, early nautiloid cephalopods, from the Middle Silurian in which the characteristic bullette is found only in early growth stages. Lowoceratids were first found in Southampton Island in the Canadian arctic. The Lowoceratidae consists so far of only two genera, ''Lowoceras'' and ''Tuylocras'', named by Foerste and Savage in 1927 and combined by Flower in 1940 as the Lowoceratidae. Both are strongly compressed, exogastric brevicones with the ventral side more narrowly rounded than the dorsal. Shells enlarge moderately to the middle of the mature body chamber, then contract gently toward the aperture. The siphuncle in each is slightly removed from the ventral margin. The siphuncle of ''Tuyloceras'', genotype ''T. percurvatum'', starts off with slender, subquadrate segments with thick rings and swollen bullettes, but later in life the segments become expanded, rings thinner, and bullettes simple and unswollen. ''Lowoceras'', genot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Nautiloids
This list of nautiloids is a comprehensive listing of all genera that have ever been included in the subclass Nautiloidea, excluding purely vernacular terms. The list includes all commonly accepted genera, but also genera that are now considered invalid, doubtful (''nomina dubia''), or were not formally published (''nomina nuda''), as well as junior synonyms of more established names, and genera that are no longer considered nautiloids. Most of the listed genera are found in Part K of the ''Treatise on Invertebrate Paleontology''. Some, added since the year of publication (1964) are found simply in various scientific journals and special publications. The named genera are based on type specimens which are housed in various museums and other academic institutions worldwide, available to interested researchers. Note that ''Allonautilus'' and ''Nautilus'' are the only extant genera. A *†'' Acanthonautilus'' *†'' Acaroceras'' *†''Acleistoceras'' *†'' Acrosphaerorthoceras'' ... [...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 d ... [...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] |
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 ''Spirula''. In the case of the cuttlefish, the siphuncle is indistinct and connects all the small chambers of that animal's highly modified shell; in the other cephalopods it is thread-like and passes through small openings in the septa (walls) dividing the camerae (chambers). Some older studies have used the term siphon for the siphuncle, though this naming convention is uncommon in modern studies to prevent confusion with a mollusc organ of the same name. Function The siphuncle is used primarily in emptying water from new chambers as the shell grows. To perform this task, the cephalopod increases the saltiness of the blood in the siphuncle, and the water moves from the more dilute chamber into the blood through osmosis. At the sa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ordovician
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 C ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Faberoceras
''Faberoceras'' is an extinct genus of prehistoric nautiloid. The nautiloids are a subclass of shelled cephalopods A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, an ... that were once diverse and numerous but are now represented by only a handful of species. See also * List of prehistoric nautiloid genera 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's Online Genus Database (CEPHALOPODA) Prehistoric nautiloid genera Discosorida {{paleo-Nautiloidea-stub ... [...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 ''Winnipegoceras ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Treatise On Invertebrate Paleontology
The ''Treatise on Invertebrate Paleontology'' (or ''TIP'') published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and covering every phylum, class, order, family, and genus of fossil and extant (still living) invertebrate animals. The prehistoric invertebrates are described as to their taxonomy, morphology, paleoecology, stratigraphic and paleogeographic range. However, taxa with no fossil record whatsoever have just a very brief listing. Publication of the decades-long ''Treatise on Invertebrate Paleontology'' is a work-in-progress; and therefore it is not yet complete: For example, there is no volume yet published regarding the post-Paleozoic era caenogastropods (a molluscan group including the whelk and periwinkle). Furthermore, every so often, previously published volumes of the ''Treatise'' are revised. Evolution of the project Raymond C. Moor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
