|
Plectronoceratidae
Plectronocerida is a primitive order from which subsequent Cephalopoda, cephalopod orders are ultimately derived.Curt Teichert, 1988. Main Features of Cephalopod Evolution. The Mollusca Vol. 12 Paleontology and Neontology of Cephalopds; Academic Pres Inc. Occurrence Plectronoceratids are known from the Upper Cambrian (upper Franconian (stage), Franconian – middle Trempealeauan) of China and North America (Minnesota, Wisconsin). Two families are recognized (Flower, 1964),Flower, Rousseau H. 1964. The Nautiloid Order Ellesmeroceratida (Cephalopoda); Memoir 12, New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico the generally straight to endogastric Plectronoceratidae and the slightly exogastric Balkoceratidae. Diagnostic characters Members of the Plectronocerida are characterized as follows. Shells are generally small, some even tiny, laterally compressed, curved (cyrtoconic) or straight (orthoconic). Most cyrtoconic forms are endogastric, with the ventral side ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plectronoceras
''Plectronoceras'' is the earliest known shelled cephalopod, dating to the Late Cambrian.''Plectronoceras'' at Fossilworks.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 Septum (marine biology), septa separated by about half a millimetre, with a siphuncle on its concave side. Its morphology matches closely to that hypothesised for the last common ancestor of all cephalopods. ''Plectronoceras'' is the type genus of the family Plectronoceratidae. Fossils of ''Plectronoceras'' have been found in the San Saba Limestone of Texas. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jiagouceras
''Jiagouceras'' is a genus of early primitive cephalopods from the Upper Cambrian of China, assigned to the Plectronoceratidae. The shell is small, nearly straight with a slight endogastric curvature and compressed cross section. The siphuncle is close to the ventral margin, with segments expanded into the chambers. ''Jiagouceras'' is found in the Wanwankou member of the Fengshan formation (Early, Middle and Upper Trempealeauan) in northern Anhui Anhui is an inland Provinces of China, province located in East China. Its provincial capital and largest city is Hefei. The province is located across the basins of the Yangtze and Huai rivers, bordering Jiangsu and Zhejiang to the east, Jiang ..., China. It is similar to '' Paraplectronoceras'' except for having more strongly expanded siphuncular segments and less concave septa. References * Chen Jun-yuan et al., 197Late Cambrian Cephalopods of North China -- Plectronocerida, Protactinocerida (Ord Nov) and Yanhecerida (Ord No ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Late Cambrian
The Furongian is the fourth and final Epoch (geology), epoch and Series (stratigraphy), series of the Cambrian. It lasted from to million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocian Stage. It is subdivided into three stages: the Paibian, Jiangshanian and the unnamed Cambrian Stage 10, 10th stage of the Cambrian. History and naming The Furongian was also known as the Cambrian Series 4, and the name replaced the older term Upper Cambrian and equivalent to the local term Hunanian. The present name was ratified by the International Commission on Stratigraphy in 2003. () means 'lotus (genus), lotus' in Mandarin and refers to Hunan which is known as the "lotus state". Definition The lower boundary is defined in the same way as the GSSP of the Paibian Stage. Both begin with the First appearance datum, first appearance of the trilobite ''Glyptagnostus reticulatus'' around million years ago. The upper boundary is the lowe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cambrian First Appearances
The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovician Period 486.85 Ma. Most of the continents lay in the southern hemisphere surrounded by the vast Panthalassa Ocean. The assembly of Gondwana during the Ediacaran and early Cambrian led to the development of new convergent plate boundaries and continental-margin arc magmatism along its margins that helped drive up global temperatures. Laurentia lay across the equator, separated from Gondwana by the opening Iapetus Ocean. The Cambrian marked a profound change in life on Earth; prior to the Period, the majority of living organisms were small, unicellular and poorly preserved. Complex, multicellular organisms gradually became more common during the Ediacaran, but it was not until the Cambrian that fossil diversity seems to rapidly increa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prehistoric Nautiloids
Prehistory, also called pre-literary history, is the period of human history between the first known use of stone tools by hominins 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 years ago. It took thousands of years for writing systems to be widely adopted, with writing having spread to almost all cultures by the 19th century. The end of prehistory therefore came at different times in different places, and the term is less often used in discussing societies where prehistory ended relatively recently. It is based on an old conception of history that without written records there could be no history. The most common conception today is that history is based on evidence, however the concept of prehistory hasn't been completely discarded. In the early Bronze Age, Sumer in Mesopotamia, the Indus Valley Civilis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". Organisms living in this zone are called benthos and include microorganisms (e.g., bacteria and fungi) as well as larger invertebrates, such as crustaceans and polychaetes. Organisms here, known as bottom dwellers, generally live in close relationship with the substrate and many are permanently attached to the bottom. The benthic boundary layer, which includes the bottom layer of water and the uppermost layer of sediment directly influenced by the overlying water, is an integral part of the benthic zone, as it greatly influences the biological activity that takes place there. Examples of contact soil layers include sand bottoms, rocky outcrops, coral, and bay mud. Description Oceans The benthic region of the ocean begins at the ... [...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, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years from the end of the Cambrian Period Megaannum, Ma (million years ago) to the start of the Silurian Period Ma. 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 per ... [...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, New ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
