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Ellesmerocerid
The Ellesmerocerida is an order of primitive cephalopods belonging to the subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician. Morphology The Ellesmerocerida are characterized by shells that are typically small, some even tiny, with close-spaced septa and relatively large ventral siphuncles. In some genera (e.g. '' Paleoceras''), the septa are uniformly spaced. Shells of ellesmerocerids are typically smooth and compressed and vary in form. They may be breviconic (short) or longiconic (elongate), straight (orthoconic) or curved (cyrtoconic). Cyrtoconic forms are usually endogastric, with longitudinally convex ventral margins. The apeces of straight forms typically have an endogastric curvature. Some may have grown to as much as 15 cm. Siphuncle segments are tubular or concave. Septal necks are short. Connecting rings which may appear layered are thick and typically wedge shaped with their maximum width at or near where th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bassleroceratidae
The Bassleroceratidae is a family of gradually expanding, smooth ellesmerocerids with a slight to moderate exogastric curvature, subcircular to strongly compressed cross section, and ventral orthochaonitc siphuncle. The ventral side is typically more sharply rounded than the dorsal side and septa are close spaced. Connecting rings are thick and slightly expanded into the siphuncle, making the segments slightly concave; characteristic of the Ellesmerocerida.Furnish and Glenister 1964a, Nautiloidea-Ellesmerocerida; Treatise on Invertebrate Paleontology, Part K Nautiloidea. Basslerocerids are limited to the Lower Ordovician and first appeared sometime in the Gasconadian, (Tremedocian) They gave rise, possibly through ''Bassleroceras'', by evolving and ever tightened curvature to the Tarphycerida and by a thinning of the connecting rings to the Graciloceratidae which are ancestral Oncocerida The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cephalopoda
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, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology. Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids. The class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses, squid, and cuttlefish; and Nautiloidea, represented by ''Nautilus'' and ''Allonautilus''. In the Coleoidea, the molluscan shell has been internalized or is absent, whereas in the Nautiloidea, the external shell remains. About 800 living species of cephalopods have been identified. Tw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bassleroceras
''Bassleroceras'' is an elongate upwardly curved, exogastric, genus with the venter on the under side more sharply rounded than the dorsum on the upper. The siphuncle is ventral, composed of thick-walled tubular segments in which connection rings thicken in towardly as in both the Ellesmerocerida and primitive Tarphycerida. ''Bassleroceras'' is the type genus of the Bassleroceratidae which Furnish and Glenister (1964) included in the Ellesmerocerida, but which Flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ... (1967) placed in the Tarphycerida. ''Bassleroceras'' gave rise to the Tarphycerida (sensu Furnish and Glenister, 1964) by evolving genera with tighter and tighter curvatures until becoming gyroconic, a character of the Estonioceratidae, a family of early tarphycerids ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clarkoceras
''Clarkoceras'' is a genus of breviconic ellesmerocerid cephalopods, one of only two genera known to have crossed from the Late Cambrian, Trempealeauan, into the Early Ordovician, Gasconadian. (Flower 1964, Teichert 1988); the other being '' Ectenolites''. Description Clarkoceras has a rapidly expanding, laterally compressed, relatively short, endogastrically cyrtoconic shell; The upper or dorsal side is more strongly convex longitudinally than the lower or ventral side is concave. Sutures are essentially straight and close spaced indicating very short camerae (chambers). The siphuncle is relatively large, 0.3 the dorsoventral dimension and is ventral, although not necessarily marginal. (Flower 1964, Furnish and Glenister 1964). Septal necks are straight, reaching about half way back to the previous septum and the connecting rings are thick and layered Taxonomy ''Clarkoceras'' was first thought by Clarke to be a pilocerid, who in 1897 give it the name ''Piloceras newton-winche ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ellesmeroceratidae
The Ellesmeroceratidae constitute a family within the cephalopod order Ellesmerocerida. They lived from the Upper Cambrian to the Lower Ordovician. They are characterized by straight and endogastric shells, often laterally compressed, so the dorso-ventral dimension is slightly greater than the lateral, with close spaced sutures having shallow lateral lobes and a generally large tubular ventro-marginal siphuncle with concave segments and irregularly spaced diaphragms. Connecting rings are thick and layered, externally straight but thickening inwardly with the maximum near the middle of the segment so as to leave concave depressions on internal siphuncle molds. Septal necks are typically orthochoanitic but vary in length from almost absent (achoanitic) to reaching halfway to the previous septum (hemichoanitic) and may even slope inwardly (loxochoanitic). Evolution and phylogeny The Ellesmeroceratidae have their derivation in the Plectronoceratidae, order Plectronocerida, in Tr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nautiloidea
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] |
Protocycloceratidae
Protcycloceratidae is an extinct family of slender, commonly annulate, members of the cephalopod order Ellesmerocerida that lived during the Early Ordovician. Protocycloceratidae, named by Kobayashi (1935), are characterized by transversely ribbed, elongate shells that may be straight or slightly curved, as to be either endogastric or exogastric.Flower 1964, Furnish & Glenister 1964 Although not universally accepted, Kröger and Mutvie (2005) revised the Protocycloceratidae to include only those ellesmerocerids that have straight transverse sutures and siphuncles with concave segments and thick connecting rings. Protocycloceratidae (''sensu'' Flower, 1964) includes the follow genera, given with brief descriptions. *'' Protocycloceras''. Strongly annulate orthocones; cross section circular; annulations and sutures transverse and essentially straight; siphuncle tubular, ventral but not marginal, about 0.3 corresponding shell diameter. Lower Ordovician, cosmopolitan. *'' Catoraphi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyclostomiceratidae
Cyclostomiceratidae is a family of Early Ordovician, (Cassinian), ellesmerocerid The Ellesmerocerida is an order of primitive cephalopods belonging to the subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician. Morphology The Ellesmerocerida are characterized by shells that ar ... cephalopods characterized by short, essentially straight shells, a fairly rapidly expanding phragmocone and a ventral siphuncle in which septal necks are almost non-existent and connecting rings are thick and layered. As typical of the Ellesmerocerida, chambers are short, septa close spaced. Genera Five genera are recognized; '' Cyclostomiceras'', '' Eocyclostomiceras'', '' Microstomiceras'', '' Paracyclostomiceras'', and '' Pictetoceras''. ''Cyclostomiceras'' and ''Paracyclostomiceras'' were described in Flower (1964). :''Cyclostomiceras'' Hyatt 1900, found in the Fort Cassin Limestone of Champlain Valley, the Smithville Formation of Arkansas, and th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acaroceratidae
Acaroceratidae is family of Upper Cambrian (Trempealeauan) nautiloid cephalopods included in the Ellesmerocerida that contains two known genera, ''Acaroceras'' and ''Weishanuceras'', both found in northern China. Acaroceratidae represent some of the earliest Ellesmeroderida, which have their origin in the Plectronoceratidae, either in ''Plectronoceras'' or some related genus. ''Acaroceras'' is known from the lower and middle Trempealeauan, upper Yenchou and overlying Wanwankou members of the Fengshan Formation. ''Weishanuceras'' is so far limited to the Wanwankou. The Acaroceratidae are characterized by small, slightly expanded, laterally compressed shells with a slight downward,(endogastric), curvature. Siphuncles are tubular, located along the ventral margin; composed of straight segments. In general conformation ''Acaroceras'' and ''Weishanuceras'' are rather similar, but differ in the details of the siphuncle. ''Acaroceras'', the earlier of the two, has a siphuncle ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyrtocerinidae
Cyrtocerinidae is a family of nautiloid cephalopods in the Order Cyrtocerinida Cyrtocerinida is an order of Ordovician nautiloid cephalopods. The order includes the families Cyrtocerinidae and Eothinoceratidae, as well as the genera '' Bathmoceras'' and '' Rummoceras''. Cyrtocerinids can be characterized by a broad si ..., previously considered ellesmerocerids. Members of the family have slightly endogastric (inwardly curved) breviconic shells with ventral siphuncles that have connecting rings thickened as lobes that project straight into the interior. Cyrtocerinidae was established by Flower 1964 for the genus '' Cyrtocerina'' Billings 1865, found at various locations across North America. The shells are generally small, laterally compressed, and dorsum more narrowly rounded than the venter. References Prehistoric nautiloid families Ordovician first appearances Ordovician extinctions Ellesmerocerida {{paleo-nautiloidea-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bathmoceratidae
''Bathmoceras'' is a primitive cephalopod genus from the Middle and Upper Ordovician. It is a member of the order Cyrtocerinida and is the only genus in the family Bathmoceratidae. Derivation At one time ''Bathmoceras'' was thought to have possibly given rise to ''Polydesmia'', once thought to have been the ancestral actinocerid. Since then revision of actinocerid phylogeny and of Ordovician stratigraphy in east Asia have cast doubts on this hypothesis. ''Bathmoceras'' is most likely derived from ''Eothinoceras'' through lengthening of the septal necks and of the inward projections of the connecting rings in a forward direction. ''Eothinoceras'' differs in that the septal necks are vestigial rather than being somewhat long as in ''Bathmoceras'' and that the inward projections of the connecting rings point straight in rather than projecting forward. Both are straight shelled or slightly exogastric. Eothinoceras is also apparently more slender. Furnish and Glenister also include ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apocrinoceratidae
Apocrinoceratidae constitutes a family of Middle Ordovician nautiloid cephalopods characterized by straight or slightly curved, transversely ribbed shells having siphuncles composed of expanded segments, short recurved septal necks, and thick connecting rings. Derivation is from the Protocycloceratidae, a family of ellesmerocerids, which differ in having straight or concave siphuncle segments, but are otherwise similar in form. Apocrinoceratidae was established by Rousseau Flower (in Flower & Teichert, 1957) repeated in Flower (1964) for the genus '' Apocrinoceras'' (Teichert & Glenister, 1954). Four additional genera are included; '' Desioceras'' and '' Glenisteroceras'' (Flower and Teichert 1957, Flower 1964),'' Bakeroceras'' (Hook and Flower 1977), and '' Paldoceras'' (Kröger ''et al'' 2009). Apocrinoceratidae was removed from the Ellesmerocerida to the Discosorida Discosorida are an order of cephalopods that lived from the beginning of the Middle Ordovician, through the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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