Kryostega Temporal range: Triassic | |
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Holotype skull on display at the Field Museum of Natural History. | |
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Genus: | Kryostega Sidor et al., 2008 |
Species: | K. collinssoni |
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Kryostega collinssoni Sidor et al., 2008 | |
Kryostega is a large temnospondyl amphibian from the Early or Middle Triassic of Antarctica. The genus is based on a single specimen collected in 1986 by a team led by paleontologist William H. Hammer of Augustana College, and now housed in the collections of the American Museum of Natural History (AMNH 24419).
The holotype consists of an incomplete snout, including portions of both the right and left premaxilla, a partial left maxilla, both lacrimals, a small portion of the left nasal, the vomer, and a fragment of the palatine. Many partial teeth are preserved, though most have been broken away at their bases. The preserved part of the skull measures 27 cm long and 21 cm wide, from which a total skull length on about one meter has been inferred (Sidor et al., 2008; p. 657). Total body length has been estimated at 4.57 meters. The specimen suffered some damage during excavation, and the ventral surface is better preserved than the dorsal side of the fossil. Presently, only a single species is recognized, K. colllinsoni, named in honor of Antarctic scientist Jim Collinson.
Sidor et al. (2008; p. 659-660) conclude that Kryostega likely belongs to either the families Heylerosauridae or the basal Mastodonsauridae within the Stereospondyli, though they also consider an alternative phylogeny, the possibility that it may belong, instead, in the Trematosauroidea, and suggest that only additional and more complete specimens of the taxon will resolve the issue.
Kryostega was discovered in beds of the upper Fremouw Formation at Gordon Valley in the central Transantarctic Mountains. This portion of the Fremouw Formation consists largely of a 300-meter thick series of crossbedded, volcaniclastic sandstones. Kryostega was found in a thin siltstone cobble conglomerate within these strata, about 70 meters from the base of the upper member. The same bed has produced remains of Cynognathus , along with a kannemeyeriid dicynodont, a gomphodont cynodont, and a second species of large temnospondyl. Sidor et al. (2008; p. 661-662) conclude that the "...inferred high paleolatitude of Gordon Valley during deposition would have subjected it to long periods of continuous darkness during the winter months," and that the discovery of a large, semiaquatic amphibian in these beds is "...evidence for unsuspected ecological diversity with the Polar Circle during the Triassic."
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Temnospondyli or temnospondyls is a diverse ancient order of small to giant tetrapods — often considered primitive amphibians — that flourished worldwide during the Carboniferous, Permian and Triassic periods, with fossils being found on every continent. A few species continued into the Jurassic and Early Cretaceous periods, but all had gone extinct by the Late Cretaceous. During about 210 million years of evolutionary history, they adapted to a wide range of habitats, including freshwater, terrestrial, and even coastal marine environments. Their life history is well understood, with fossils known from the larval stage, metamorphosis, and maturity. Most temnospondyls were semiaquatic, although some were almost fully terrestrial, returning to the water only to breed. These temnospondyls were some of the first vertebrates fully adapted to life on land. Although temnospondyls are amphibians, many had characteristics such as scales and armour-like bony plates that distinguish them from the modern soft-bodied lissamphibians.
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Hyperokynodon is an extinct genus of trematosaurian temnospondyl within the family Trematosauridae. Fossils have been found in Germany. While most trematosaurids existed during the Early Triassic, Hyperokynodon has been found in Late Triassic deposits, making it the youngest known trematosaurid. Hyperokynodon was known since 1852, but it was not identified as a trematosaurid until 1987. The type and only species is H. keuperinus.
Rhigosaurus glacialis is a species of therocephalian therapsid. Its fossilized remains have been found in the Fremouw Formation of Antarctica. Part of a juvenile skull was found near Mount Kenyon, Antarctica. The holotype of the partial skull shows evidence of promiment upper and lower canine teeth.
Micropholis is an extinct genus of dissorophoid temnospondyl. Fossils have been found from the Lystrosaurus Assemblage Zone of the Karoo Basin in South Africa and are dated to the Induan. Fossils have also been found from the lower Fremouw of Antarctica.Micropholis is the only post-Permian dissorophoid and the only dissorophoid in what is presently the southern hemisphere and what would have been termed Gondwana during the amalgamation of Pangea.
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This list of fossil amphibians described in 2018 is a list of new taxa of fossil amphibians that were described during the year 2018, as well as other significant discoveries and events related to amphibian paleontology that occurred in 2018.
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