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''Youngina'' is an extinct genus of diapsid reptile from the Late Permian Beaufort Group (''Tropidostoma''-''Dicynodon'' zones) of the Karoo Red Beds of South Africa.〔Smith R., Evans, S. 1996. New Material of ''Youngina'': Evidence of Juvenile Aggregation in Permian Diapsid Reptiles. ''Palaeontology'', 39(2): 289-303.〕 This, and a few related forms, make up the family Younginidae, within the Order Eosuchia (proposed by Broom in 1924). Eosuchia, having become a dustbin for many probably distantly-related primitive diapsid reptiles ranging from the Late Carboniferous to the Eocene, Romer proposed that it be replaced by Younginiformes (that included Younginidae and the Tangasauridae, ranging from the Permian to the Triassic). ''Youngina'' is known from several specimens. Many of these were attributed to as separate genera and species (such as ''Youngoides'' and ''Youngopsis''), but it was later realized that they were not distinct from ''Y. capensis''.〔〔Evans S. E. 1987. The braincase of ''Youngina capensis'' (Reptilia: Diapsida; Permian). ''N. Jahrb. Geol. Paläont. Monats.'' 1984: 193-203.〕 The holotype specimen of ''Youngina'' was described briefly in the early 20th century.〔Broom, R., 1914, A new thecodont reptile: Proceedings of the Zoological Society of London, series B, v. 84, p. 1072-1077.〕 The "''Youngoides romeri''" specimen was first attributed to ''Youngina'',〔Olson, EC (1936). Notes on the Skull of Youngina Capensis Broom. Journal of Geology 44(4): 523-533. http://www.jstor.org/stable/30068180〕 but later given its eponymous and separate designation in a later paper.〔Olson, E. C., and Broom R., 1937, New genera and species of tetrapods form the Karroo beds of South Africa: Journal of Paleontology, v. 11, p. 613-619.〕 ''Acanthotoposaurus''〔EVANS S. E.; VAN DEN HEEVER J. A., 1987. A new reptile (Reptilia: Diapsida) from the Upper Permian Daptocephalus zone of South Africa = Un nouveau reptile (Reptilia: Diapsida) provenant de la zone à Daptocephalus du Permien supérieur d'Afrique du Sud. South African journal of science, vol. 83, no. 11, pp. 724-730.〕 is also a junior synonym of ''Youngina''.〔Reisz RR.；Modesto SP.；Scott D. 2000. Acanthotoposaurus bremneri and the origin of the Triassic archosauromorphreptile fauna of South Africa. South African journal of science, vol. 96, no. 8.〕 ''Youngina'' was once thought to be closely related to ''Acerosodontosaurus'', and more distantly to tangasaurids (''Kenyasaurus'', ''Hovasaurus'', ''Thadeosaurus'', and ''Tangasaurus''), but the monophyly of younginiforms has not been demonstrated in published analyses of diapsid reptiles, and it is likely this group is paraphyletic. ''Acerosodontosaurus'' is probably closer to other former "younginiforms", rather than being closely related to ''Youngina''.〔Bickelmann, Müller, and Reisz. 2009. The enigmatic diapsid ''Acerosodontosaurus piveteaui'' (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of "younginiform" reptiles. ''Canadian Journal of Earth Sciences'', 46 (9): 651-661.〕 Below is a cladogram from the analysis of Reisz ''et al.'' (2011) showing the phylogenetic position of ''Youngina'' among early diapsids: |2= }} }} }} }} }} }} }} ''Youngina'' could have been a moderately sized early reptile (skull length < ), comparable to size to some medium-sized monitor lizards such as Gould's monitor.〔Gow CE (1975), ''Palaeontologia africana''.〕 The braincase anatomy was recently redescribed〔Gardner, Nicholas M., Holliday, Casey M., and O'Keefe, F. Robin 2010. The Braincase of Youngina capensis (Reptilia, Diapsida): New Insights from High-Resolution CT Scanning of the Holotype. Palaeontologica Electronica 13(3); 19A: 16p. http://palaeo-electronica.org/2010_3/217/〕 and ''Youngina'' shows a mosaic of features found in more primitive diapsids and more derived taxa such as archosauromorphs and lepidosauromorphs suggesting a non-orthogenetic evolution of these characters. Though the palatobasal articulation is open,〔 it was probably immobile, similar to the skull of the tuatara,〔Johnston, P 2010. The constrictor dorsalis musculature and basipterygoid articulation in Sphenodon. Journal of Morphology. 〕 contrary to some earlier claims made about the metakinetic mobility of basicranial joints in ''Youngina'' and other early diapsid reptiles.〔Evans, S.E. 1980. The skull of a new eosuchian reptile from the Lower Jurassic of South Wales, Zoological Journal of the Linnean Society, 70:203-264. 〕 ==References== 〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Youngina」の詳細全文を読む スポンサード リンク
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