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Osteostraci Genera
The class Osteostraci (meaning "bony shells") is an extinct taxon of bony-armored jawless fish, termed "ostracoderms", that lived in what is now North America, Europe and Russia from the Middle Silurian to Late Devonian. Anatomically speaking, the osteostracans, especially the Devonian species, were among the most advanced of all known agnathans. This is due to the development of paired fins, and their complicated cranial anatomy. The osteostracans were more similar to lampreys than to jawed vertebrates in possessing two pairs of semicircular canals in the inner ear, as opposed to the three pairs found in the inner ears of jawed vertebrates. They are thought to be the sister-group to pituriaspids, and together, these two taxa of jawless vertebrates are the sister-group of gnathostomes. Several synapomorphies support this hypothesis, such as the presence of: sclerotic ossicles, paired pectoral fins, a dermal skeleton with three layers (a basal layer of isopedin, a middle layer of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dorsal Fin
A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through convergent evolution they have independently evolved external superficial fish-like body plans adapted to their marine environments, including most numerously fish, but also mammals such as cetaceans (whales, dolphins, and porpoises), and even extinct ancient marine reptiles such as various known species of ichthyosaurs. Most species have only one dorsal fin, but some have two or three. Wildlife biologists often use the distinctive nicks and wear patterns which develop on the dorsal fins of large cetaceans to identify individuals in the field. The bony or cartilaginous bones that support the base of the dorsal fin in fish are called ''pterygiophores''. Functions The main purpose of the dorsal fin is to stabilize the animal against rollin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wladysagitta
''Wladysagitta'' is an extinct genus of osteostracan jawless fish that existed during the lower Devonian period of what is now Podolia, Ukraine. This taxon was named in honor of Polish paleontologist Dr. Władysław Zych (1899–1981), and from the Latin sagitta, meaning arrow, which is in reference to the arrow-like shape of its skull.Voichyshyn, Victor. (2006). New osteostracans from the Lower Devonian terrigenous deposits of Podolia, Ukraine. Acta Palaeontologica Polonica. 51. Description ''Wladysagitta'', like other osteostracans, possesses very advanced features for an agnathan; namely, an armored headshield with complicated cranial anatomy, paired fins and rows of plated scales. It is remarkable among osteostracans for possessing a rostral process, a beaklike structure unusual for this class, which usually possesses blunted, horseshoe-shaped headshields. It is also distinct for being ornamented by a number of unusually prominent, thorn-like tubercles on its headshield as pres ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hemicyclaspis
''Hemicyclaspis'' ( or 'semicircle plate') is an extinct genus of primitive jawless fish, closely related to ''Cephalaspis'', that lived in the Late Silurian ( Pridoli) to Devonian period in what is now Europe and North America. A typical cephalaspid, ''Hemicyclaspis'' had a heavily armored, shovel-shaped headshield. It is thought to have been a better swimmer than most of its relatives because of its powerful tail, stabilizing dorsal fin and the keel-shaped hydrodynamic In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) and ... edges of its head shield. ''Hemicyclaspis'' probably foraged the ocean floor for food. ''Hemicyclaspis'' grew to a length of 5 inches (13 centimeters) and would most likely have fed on particles from the muddy sea bed. References * Parker, Steve. Dinosaurus: th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ateleaspis
''Ateleaspis'' is an extinct genus of primitive ostracoderm fish that lived in the Early Silurian to Early Devonian periods. Like other ostracoderms, ''Ateleaspis'' had a head shield similar to that of ''Cephalaspis''. Species from Silurian period were found in Norway and Scotland, but now has been found also in Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of ... from Early Devonian period. Description ''Ateleaspis'' possibly is the most basal vertebrate with paired fins. ''Ateleaspis'' was a small fish (about 15 – 20 cm) and had a flat headshield and a narrow trunk covered by brick-like scales. References External links Ateleaspis at PalaeosAteleaspis species location & chronology Osteostraci genera Paleozoic jawless fish Fossils of Norway Fossils of Gr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ateleaspididae
Ateleaspididae is a prehistoric jawless fish family in the class Osteostraci The class Osteostraci (meaning "bony shells") is an extinct taxon of bony-armored jawless fish, termed "ostracoderms", that lived in what is now North America, Europe and Russia from the Middle Silurian to Late Devonian. Anatomically speaking, ....Sansom, R. S. (2009). "Phylogeny, classification and character polarity of the Osteostraci (Vertebrata)". Journal of Systematic Palaeontology 7: 95–11. References External links Osteostraci Prehistoric jawless fish families {{Paleo-jawless-fish-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
