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Cephalopod Evolution
The cephalopods have a long geological history, with the first nautiloids found in late Cambrian strata, and purported stem-group representatives present in the earliest Cambrian lagerstätten. The class developed during the middle Cambrian, and underwent pulses of diversification during the Ordovician period to become diverse and dominant in the Paleozoic and Mesozoic seas. Small shelly fossils such as '' Tommotia'' were once interpreted as early cephalopods, but today these tiny fossils are recognized as sclerites of larger animals, and the earliest accepted cephalopods date to the Middle Cambrian Period. During the Cambrian, cephalopods are most common in shallow near-shore environments, but they have been found in deeper waters too. Cephalopods were thought to have "undoubtedly" arisen from within the tryblidiid monoplacophoran clade. However genetic studies suggest that they are more basal, forming a sister group to the Scaphopoda but otherwise basal to all other major moll ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cephalopod
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 ident ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plectronoceras
''Plectronoceras'' is the earliest known shelled cephalopod, dating to the Late Cambrian.''Plectronoceras'' at .org None of the fossils are complete, and none show the apex or aperture of the shell. Approximately half of its shell was filled with septa; 7 were recorded in a shell. Its shell contains transverse separated by about half a millimetre, with a |
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] |
Septum (marine Biology)
Septa (singular septum) are thin walls or partitions between the internal chambers (camerae) of the shell of a cephalopod, namely nautiloids or ammonoids. As the creature grows, its body moves forward in the shell to a new living chamber, secreting septa behind it. This adds new chambers to the shell, which can be clearly seen in cross-sections of the shell of the living nautilus, or in ammonoid and nautiloid fossils. The septa are attached to the inside wall of the shell, thus dividing the phragmocone into camerae. Where the septum meets the shell a suture line forms; in some ammonoids these lines became extremely complex and elaborate, providing strength without the necessity of added weight. Elaborate sutures allowed for thinner shells, and hence less time needed for shell growth and less time spent in the vulnerable juvenile stage. The nature and structure of the septa, as with the camerae, and siphuncle, and the presence or absence of deposits, are important in classific ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fengshan Formation
Fengshan may refer to: *Feng Shan, Chinese religious ritual Geographic names People's Republic of China *Fengshan County, Guangxi () ;Subdistricts () *Fengshan Subdistrict, Shanwei, in Cheng District, Shanwei, Guangdong *Fengshan Subdistrict, Fengcheng, Liaoning * Fengshan Subdistrict, Lüliang, in Lishi District, Lüliang, Shanxi * Fengshan Subdistrict, Yuyao, Zhejiang ;Towns Written as "": * Fengshan, Hua'an County, Fujian * Fengshan, Xiaochang County, Hubei Written as "": * Fengshan, Luoyuan County, Fujian * Fengshan, Bobai County, Guangxi * Fengshan, Liucheng County, Guangxi * Fengshan, Guizhou, in Fuquan * Fengshan, Fengning County, Hebei * Fengshan, Shijiazhuang, in Jingxing Mining District, Shijiazhuang, Hebei * Fengshan, Tonghe County, Heilongjiang * Fengshan, Luotian County, Hubei *Fengshan, Jinggu County, Jinggu Dai and Yi Autonomous County, Yunnan * Fengshan, Fengqing County, Fengqing County, Yunnan ;Townships Written as "": *Fengshan Township, Heilongjiang, in H ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tannuella
''Tannuella'' is a genus of helcionellids known from Lower Cambrian strata. It has a high, septate shell similar to that of hypseloconids such as ''Knightoconus ''Knightoconus antarcticus'' is an extinct species of fossil monoplacophoran from the Cambrian Minaret Formation of Antarctica. It is thought to represent an ancestor to the cephalopods. It had a chambered conical shell, but lacked a siphuncl ...'' . These genera were once considered ancestral cephalopods, but are more broadly assigned to the helconellids (or putatively the tergomyans); i.e. "Cambrian monoplacophora". References Helcionellidae Prehistoric cephalopod genera Cambrian molluscs Paleozoic invertebrates of Oceania Paleozoic animals of Asia {{paleo-cephalopod-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eoclarkoceras
''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-winchell ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ectenolites
''Ectenolites'' is a genus of small, slender, cylindrical Ellesmeroceratids that resemble '' Ellesmeroceras'' but are smaller and proportionally narrower. Septa, as typical for ellesmerocerids, are close spaced with shallow lobes on either flank. The body chamber is proportionally long, the shell itself slightly compressed. The dorsal side at the beginning of the shell, opposite the aperture and body chamber, is strongly convex so to produce a sense of endogastric curvature with the apex and 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 ... aligned.Flower R.H.1964, The Nautiloid Order Ellesmeroceratida (Cephalopoda). Memoir 12, New Mexico Bureau of Mines and Mineral Resources, Socorro, NM The siphuncle in ''Ectenolites'' lies along the ventral side; is tubular, composed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arthropod cuticle, cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages. Arthropods are bilaterally symmetrical and their body possesses an exoskeleton, external skeleton. In order to keep growing, they must go through stages of moulting, a process by which they shed their exoskeleton to reveal a new one. Some species have wings. They are an extremely diverse group, with up to 10 million species. The haemocoel, an arthropod's internal cavity, through which its haemolymph – analogue of blood – circulates, accommodates its interior Organ (anatomy), organs; it has an open circulatory system. Like their exteriors, the internal or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nectocaris
''Nectocaris'' is a genus of squid-like animal of controversial affinities known from the Cambrian period. The initial fossils were described from the Burgess Shale of Canada. Other similar remains possibly referrable to the genus are known from the Emu Bay Shale of Australia and Chengjiang Biota of China. ''Nectocaris'' was a free-swimming, predatory or scavenging organism. This lifestyle is reflected in its binomial name: ''Nectocaris'' means "swimming shrimp" (from the Ancient Greek , ', meaning "swimmer" and , ', "shrimp"; , ', means "wing"). Two morphs are known: a small morph, about an inch long, and a large morph, anatomically identical but around four times longer. Nectocaridids have controversial affinities. Some authors have suggested that they represent the earliest known cephalopods. However, their morphology is strongly dissimilar to confirmed early cephalopods, and thus their affinities to cephalopods and even to molluscs more broadly are rejected by most authors. T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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