|
Thelodont
Thelodonti (from Greek: "nipple teeth")Maisey, John G., Craig Chesek, and David Miller. Discovering fossil fishes. New York: Holt, 1996. is a class of extinct Palaeozoic jawless fishes with distinctive scales instead of large plates of armor. There is much debate over whether the group represents a monophyletic grouping, or disparate stem groups to the major lines of jawless and jawed fish. Thelodonts are united in possession of "thelodont scales". This defining character is not necessarily a result of shared ancestry, as it may have been evolved independently by different groups. Thus the thelodonts are generally thought to represent a polyphyletic group, although there is no firm agreement on this point. On the basis that they are monophyletic, they are reconstructed as being ancestrally marine and invading freshwater on multiple occasions. "Thelodonts" were morphologically very similar, and probably closely related, to fish of the classes Heterostraci and Anaspida, diff ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fish Scale
A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as well as possible hydrodynamic advantages. The term ''scale'' derives from the Old French , meaning a shell pod or husk. Scales vary enormously in size, shape, structure, and extent, ranging from strong and rigid armour plates in fishes such as shrimpfishes and boxfishes, to microscopic or absent in fishes such as eels and anglerfishes. The morphology (biology), morphology of a scale can be used to identify the species of fish it came from. Scales originated within the jawless ostracoderms, ancestors to all jawed fishes today. Most bony fishes are covered with the cycloid scales of salmon and carp, or the ctenoid scales of perch, or the ganoid scales of sturgeons and gars. Cartilaginous fishes (sharks and rays) are covered with placoi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Furcacauda
''Furcacauda'' is a genus of thelodontid agnathan from the Lower Devonian of Canada, and is the type genus of the order Furcacaudiformes Furcacaudiformes is an extinct order of jawless fish in the class Thelodonti. Because the paucity of intact fossils, especially since some families are known entirely from scale fossils, taxonomy of thelodonts is based primarily on scale morphol .... Furcacaudiform thelodontids were deep water jawless vertebrates with symmetrical fork and lobed-finned tails and scales smaller than typical loganellid and nikoliviid thelodonti scales. Furcacaudiform thelodonts are noted as having a laterally compressed body, large anterior eyes, slightly posterior, lateral, and vertical to a small mouth, and a condensed curved row of branchial openings (gills) directly posterior to the eyes. Many but not all had laterally paired fins. Wilson and Caldwell also note the presence of a caudal peduncle and a long caudal fin made of two large lobes, one dorsal and on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Agnatha
Agnatha (; ) or jawless fish is a paraphyletic infraphylum of animals in the subphylum Vertebrata of the phylum Chordata, characterized by the lack of jaws. The group consists of both extant taxon, living (Cyclostomi, cyclostomes such as hagfishes and lampreys) and Extinction, extinct clades (e.g. conodonts and Cephalaspidomorphi, cephalaspidomorphs, among others). They are sister taxon, sister to vertebrates with jaws known as gnathostomes, who evolution, evolved from jawless ancestors during the early Silurian by developing folding joint, articulations in the first pairs of gill arches. Sequencing, Molecular data, both from rRNA and from mtDNA as well as Embryology, embryological data, strongly supports the hypothesis that both groups of living agnathans, hagfishes and lampreys, are more closely related to each other than to Gnathostomata, jawed fish, forming the Class (biology), superclass Cyclostomi. The oldest fossil agnathans appeared in the Cambrian. Living jawless fish c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Furcacaudiformes
Furcacaudiformes is an extinct order of jawless fish in the class Thelodonti. Because the paucity of intact fossils, especially since some families are known entirely from scale fossils, taxonomy of thelodonts is based primarily on scale morphology. A 2009 assessment of thelodont taxonomy by Wilson and Märss merges the orders Loganelliiformes, Katoporiida and Shieliiformes into Thelodontiformes, places families Lanarkiidae and Nikoliviidae into Furcacaudiformes (because of scale morphology) and establishes Archipelepidiformes Archipelepidiformes is an order of extinct jawless fishes in the class Thelodonti. Archipelepidiforms are regarded as the basalmost thelodonts primarily because the histology and morphology of archipelepidiforms have many similarities with the h ... as the basal-most order. References External links * Thelodonti Devonian jawless fish Prehistoric jawless fish orders {{Devonian-jawless-fish-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Archipelepidiformes
Archipelepidiformes is an order of extinct jawless fishes in the class Thelodonti. Archipelepidiforms are regarded as the basalmost thelodonts primarily because the histology and morphology of archipelepidiforms have many similarities with the histology and morphology of pteraspidomorphi, pteraspidomorphs, hinting that the two groups share a common ancestor, and hinting that archipelepidiforms retain many primitive features from this common ancestor.Soehn, K. L., Märss, T., Caldwell, M. W. & Wilson, M. V. H., 2001: New and biostratigraphically useful thelodonts from the Silurian of the Mackenzie Mountains, Northwest Territories, Canada. Journal of Vertebrate Paleontology, 21: 651-65/ref> Wilson, Mark VH, and Tiiu Märss. "Thelodont phylogeny revisited, with inclusion of key scale-based taxa." Estonian Journal of Earth Sciences 58.4 (2009): 297œ310/ref> Currently, only whole body fossils of ''Archipelepis'' are known: these fossils show that archipelepids were tadpole-like anima ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thelodontiformes
Thelodontiformes is an extinct order of jawless fish of the Silurian.Kiaer, J., 1932: New coelolepids from the Upper Silurian on Oesel (Esthonia). Eesti Loodusteaduse Arhiiv, Seeria 1, 10: 167-176. Because the paucity of intact fossils, especially since some families are known entirely from scale fossils, taxonomy of thelodonts is based primarily on scale morphology. A recent assessment of thelodont taxonomy by Wilson and Märss in 2009 merges the order (biology), orders Loganelliiformes, Katoporiida and Shieliiformes into Thelodontiformes, places family (biology), families Lanarkiidae and Nikoliviidae into Furcacaudiformes (because of scale morphology) and establishes Archipelepidiformes as the basal-most order.Wilson, Mark VH, and Tiiu Märss. "Thelodont phylogeny revisited, with inclusion of key scale-based taxa." Estonian Journal of Earth Sciences 58.4 (2009): 297œ310/ref> References External links * Thelodonti Silurian jawless fish Prehistoric jawless fish ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Late Devonian Extinction
The Late Devonian mass extinction, also known as the Kellwasser event, was a mass extinction event which occurred around 372 million years ago, at the boundary between the Frasnian and Famennian ages of the Late Devonian period.Racki, 2005McGhee, George R. Jr, 1996. The Late Devonian Mass Extinction: the Frasnian/Famennian Crisis (Columbia University Press) It is placed as one of the "Big Five" most severe mass extinction events in Earth's history, with likely around 40% of marine species going extinct, though the degree of severity is contested. A second mass extinction called the Hangenberg event, also known as the end-Devonian extinction, occurred 13 million years later around 359 million years ago, bringing an end to the Famennian and Devonian, as the world transitioned into the Carboniferous Period. The effects of the two extinction events have historically been conflated, and both events collectively profoundly reshaped marine ecosystems. Although it is well established ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lanarkia
''Lanarkia'' is a genus of extinct thelodont agnathan which existed in what is now Scotland and Canada during the upper Silurian period.''Lanarkia horrida'' at www.fossilmuseum.net. Description Lanarkia were very small fish specifically 30-45 cm in length that would have been possible prey toeurypterids
Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 million years ago. The ... .
References [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gnathostome
Gnathostomata (; from Ancient Greek: (') 'jaw' + (') 'mouth') are jawed vertebrates. Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all extant vertebrates, including all living bony fishes (both ray-finned and lobe-finned, including their terrestrial tetrapod relatives) and cartilaginous fishes, as well as extinct prehistoric fish such as placoderms and acanthodians. Most gnathostomes have retained ancestral traits like true teeth, a stomach, and paired appendages ( pectoral and pelvic fins, limbs, wings, etc.). Other traits are elastin, horizontal semicircular canal of the inner ear, myelinated neurons, and an adaptive immune system which has discrete secondary lymphoid organs (spleen and thymus) and uses V(D)J recombination to create antigen recognition sites, rather than using genetic recombination in the variable lymphocyte receptor gene. It is now assumed that Gnathostomata evolved from ancestors that already possessed two pairs ... [...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] |
