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Astraspis
''Astraspis'' ('star shield') is an extinct genus of primitive jawless fish from the Ordovician of Central North America including the Harding Sandstone of Colorado and Bighorn Mountains of Wyoming. It is also known from Bolivia.Sacabambaspis janvieri. PY Gagnier - Vertébré ordovicien de Bolivie, 1993 It is related to other Ordovician fishes, such as the South American ''Sacabambaspis'', and the Australian ''Arandaspis''. Description Nearly complete fossils suggest the living animals were about in length. The body had a mobile tail covered with small protective plate-like scales of less than and a forebody covered with plate-like scales larger than . The specimen from North America (described by Sansom et al., 1997) is to have had relatively large, laterally-positioned eyes and a series of eight gill openings on each side. The specimen was generally oval in cross-section. The protective bony plates covering the animal were composed of aspidin (chemically similar to mod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astraspis Desiderata
''Astraspis'' ('star shield') is an extinct genus of primitive jawless fish from the Ordovician of Central North America including the Harding Sandstone of Colorado and Bighorn Mountains of Wyoming. It is also known from Bolivia.Sacabambaspis janvieri. PY Gagnier - Vertébré ordovicien de Bolivie, 1993 It is related to other Ordovician fishes, such as the South American ''Sacabambaspis'', and the Australian ''Arandaspis''. Description Nearly complete fossils suggest the living animals were about in length. The body had a mobile tail covered with small protective plate-like scales of less than and a forebody covered with plate-like scales larger than . The specimen from North America (described by Sansom et al., 1997) is to have had relatively large, laterally-positioned eyes and a series of eight gill openings on each side. The specimen was generally oval in cross-section. The protective bony plates covering the animal were composed of aspidin (chemically similar to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arandaspis
''Arandaspis prionotolepis'' is an extinct species of jawless fish that lived in the Ordovician period, about 480 to 470 million years ago. Its remains were found in the Stairway Sandstone near Alice Springs, Australia in 1959, but it was not determined that they were the oldest known vertebrates until the late 1960s. ''Arandaspis'' is named after a local Aboriginal tribe, the Aranda (now currently called Arrernte). Description ''Arandaspis'' was about long, with a streamlined body covered in rows of knobbly armoured scutes. The front of the body and the head were protected by hard plates with openings for the eyes, nostrils and gills. It probably was a filter-feeder. It had no fins; its only method of propulsion was the use of its vertically flattened tail. As a result, it probably swam in a fashion similar to a modern tadpole. See also * ''Astraspis'' * ''Sacabambaspis ''Sacabambaspis'' is an extinct genus of jawless fish that lived in the Ordovician period. ''S ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Field Museum Of Natural History
The Field Museum of Natural History (FMNH), also known as The Field Museum, is a natural history museum in Chicago, Illinois, and is one of the largest such museums in the world. The museum is popular for the size and quality of its educational and scientific programs, and its extensive scientific-specimen and artifact collections. The permanent exhibitions, which attract up to two million visitors annually, include fossils, current cultures from around the world, and interactive programming demonstrating today's urgent conservation needs. The museum is named in honor of its first major benefactor, Marshall Field, the department-store magnate. The museum and its collections originated from the 1893 World's Columbian Exposition and the artifacts displayed at the fair. The museum maintains a temporary exhibition program of traveling shows as well as in-house produced topical exhibitions. The professional staff maintains collections of over 24 million specimens and objects tha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ordovician Jawless Fish
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 Cambrian Perio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pteraspidomorphi Genera
Pteraspidomorphi is an extinct class of early jawless fish. They have long been regarded as closely related or even ancestral to jawed vertebrates, but the few characteristics they share with the latter are now considered as basal traits for all vertebrates. Characteristics Pteraspidomorphs are characterized by their massive dermal head armour having large, median, ventral and dorsal plates or shields. Janvier, Philippe (1997Pteraspidomorphi''The Tree of Life Web Project''. The fossils show extensive shielding of the head. Many had hypocercal tails in order to generate lift to increase ease of movement through the water for their armoured bodies, which were covered in dermal bone. They also had sucking mouth parts and some species may have lived in fresh water. Most pteraspidomorphs were marine, but lived very near to the shore, in lagoons and deltas. Some groups are thought to have been fresh water-dwelling. They were certainly bottom-dwellers, as shown by traces of abrasio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Palaeos
Palaeos.com is a web site on biology, paleontology, phylogeny and geology and which covers the history of Earth. The site is well respected and has been used as a reference by professional paleontologists such as Michael J. Benton, the professor of vertebrate palaeontology in the Department of Earth Sciences at the University of Bristol.Benton, ''Vertebrate Paleontology''Third Edition. Blackwell Publishing. It is frequently cited in ''Science'' Online. Palaeos.com was started by Toby White and Alan Kazlev;Mitch Leslie (ed.) (2006): Recalled to Life, ''Science Magazine'', vol.31PDFp.2 (also iFossil Footnotes) the pair were later joined by Chris Taylor, Mikko Haaramo of the Department of Geology at the University of Helsinki, and Chris Clowes. It features professional-level, yet readable articles about: * Palaeontology, evolution and systematics * Geochronology, earth systems and time scale * Diversity of life and ecology The site's developers have started a wiki''Palaeos.org'' which ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dentine
Dentin () (American English) or dentine ( or ) (British English) ( la, substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by enamel on the crown and cementum on the root and surrounds the entire pulp. By volume, 45% of dentin consists of the mineral hydroxyapatite, 33% is organic material, and 22% is water. Yellow in appearance, it greatly affects the color of a tooth due to the translucency of enamel. Dentin, which is less mineralized and less brittle than enamel, is necessary for the support of enamel. Dentin rates approximately 3 on the Mohs scale of mineral hardness. There are two main characteristics which distinguish dentin from enamel: firstly, dentin forms throughout life; secondly, dentin is sensitive and can become hypersensitive to changes in temperature due to the sensory function of odontoblasts, especially when enamel recedes and dentin channels become ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tubercles
In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projection, but it has slightly different meaning depending on which family of plants or animals it is used to refer to. In the case of certain orchids and cacti, it denotes a round nodule, small eminence, or warty outgrowth found on the lip. They are also known as podaria (singular ''podarium''). When referring to some members of the pea family, it is used to refer to the wart-like excrescences that are found on the roots. In fungi In mycology, a tubercle is used to refer to a mass of hyphae from which a mushroom is made. In animals When it is used in relation to certain dorid nudibranchs such as '' Peltodoris nobilis'', it means the nodules on the dorsum of the animal. The tubercles in nudibranchs can present themselves in different ways: ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Teeth
A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tearing food, for defensive purposes, to intimidate other animals often including their own, or to carry prey or their young. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from the embryonic germ layer, the ectoderm. The general structure of teeth is similar across the vertebrates, although there is considerable variation in their form and position. The teeth of mammals have deep roots, and this pattern is also found in some fish, and in crocodilians. In most teleost fish, however, the teeth are attached to the outer surface of the bone, while in lizards they are attached to the inner surface of the jaw by one side. In cartilaginous fish, s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shark
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii) and are the sister group to the rays. However, the term "shark" has also been used to refer to all extinct members of Chondrichthyes with a shark-like morphology, such as hybodonts and xenacanths. The oldest modern sharks are known from the Early Jurassic. They range in size from the small dwarf lanternshark (''Etmopterus perryi''), a deep sea species that is only in length, to the whale shark (''Rhincodon typus''), the largest fish in the world, which reaches approximately in length. Sharks are found in all seas and are common to depths up to . They generally do not live in freshwater, although there are a few known exceptions, such as the bull shark and the river shark, which can be found in both seawater and fresh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
