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Perimecoceras
''Perimecoceras'' is a genus of nothoceratids, nautilitoids in the order Oncocerida, with a slowly expanding, compressed, cyrtoconic shell, known from the Upper Silurian of central Europe. ''Perimecoceras'' is similar in general form to the oncoceratid genus '' Oonoceras'' from which it may have been derived, but differs in having a longer body chamber in proportion and in having concave segments to its siphuncle. It as also the most likely ancestral nothoceratid, probably giving rise to '' Blakeoceras'' and other Nothoceratidae. ''Perimecoceras'' probably lived on the sea floor, body chamber horizontal, phragmocone behind arched upward away from the bottom, using a combination of crawling and jet-swimming as it moved about. References * Sweet, W.C. 1964; Nautiloidea -Oncocerida; 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 ... [...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] |
Blakeoceras
''Blakeoceras'' is a nautiloid cephalopod from the Oncocerida family Nothoceratidae with a curved shell that lived in shallow seas from the Silurian to the Middle Devonian in what has become Europe. The shell of ''Blakeoceras'' is moderately curved (cyrtoconic) with the ventral side on the outer curvature (exogastric) Chambers in the phragmocone are short and wide, separated by straight, close spaced septa. Body chamber short. Siphuncle ventro-marginal, with internal, radial actinosiphonate deposits and concave segments. ''Blakeocers'' is similar to ''Perimecoceras'' in general form but is more broadly expanded and has a proportionally shorter body chamber. '' Conostichoceras'' is less strongly curved and widens more laterally. '' Turnoceras'' is more strongly curved and has a much greater expansion. ''Conostichoceras'' and ''Turnoceras'' are also more breviconic (shorter). ''Blakeoceras'' is an early nothoceratid possibly derived from ''Perimecoceras'' which has its or ... [...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] |
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] |
Oonoceras
''Oonoceras'' is an extinct genus of fossil cephalopods included in the nautiloid order Oncocerida and the family Oncoceratidae from the Middle Ordovician to Middle Silurian of North America and Europe, arbitrarily included in the Slender Oncoceratidae. Shells of this genus are generally slender, gradually expanding, exograstric cyrtocones with an ovoid cross section more narrowly rounded ventrally than dorsally as in (e.g.) ''Bassleroceras''. Curvature is generally greater than that in ''Oocerina ''Oocerina'' is an extinct genus of nautiloid cephalopods that lived during the Late Silurian of Europe, Russia, and North America. ''Oocerina'', included in the oncoerid family Oncoceratidae and arbitrarily within the Slender Oncoceratidae, i ...'' but less than that of '' Richardonoceras'' or '' Dunleithoceras''. The siphuncle of ''Oonoceras'' is cyrtochoanitic. Septal necks flare outwardly and unlike ''Oocerina'', are empty. Segments are either slightly or broadly expanded i ... [...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 sam ... [...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 Common periwinkle, periwinkle). Furthermore, every so often, previously published volumes of the ''Treatise'' are revised. Evolution of the proje ... [...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] |
