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''Diarthrognathus'' ("Two joint jaw") was a genus of synapsid, known from fossil evidence found in South Africa.〔(''Diarthrognathus'' ) - Encyclopædia Britannica.〕 and first described in 1958 by A.W. Crompton.〔Rieppel, Olivier. ''(Evolutionary Theory and the Creation Controversy )'', p. 190 (Springer, 2010).〕 The creature lived during the Late Triassic to Early Jurassic periods, about 200 million years ago.〔〔 It was carnivorous and small, slightly smaller than ''Thrinaxodon'' which was under long.〔Crompton, A.W. "Masticatory Function in Non-Mammalian Cynodonts and Early Mammals" in ''(Functional Morphology in Vertebrate Paleontology )'', p. 64 (J. Thomason, ed., Cambridge University Press 1997).〕 ''Diarthrognathus'' possesses a jaw structure that is similar to both mammals and more basal synapsids. Its primitive jaw joint is located between the quadrate and articular bones, and its derived, mammalian jaw joint is located between the squamosal and dentary bones.〔 Prothero, Donald. ''(Evolution: What the Fossils Say and Why It Matters )'', p. 278 (Columbia University Press, 2013).〕 The articular and quadrate bones evolved to become two of the middle-ear bones in mammals.〔''(The Mesozoic Era: Age of Dinosaurs )'', p. 183 (Britannica Educational Publishing, Rosen Publishing Group, 2010).〕 The transition exemplified by ''Diarthrognathus'' suggests that natural selection favored animals with a more powerful bite.〔"(How Animals Got Their Bite )", ''New Scientist'', p. 146 (July 18, 1963).〕 At one time, ''Diarthrognathus'' was thought to be synonymous with ''Pachygenelus''. However, in 1980, newly discovered fossils revealed sufficient differences to warrant separate genera.〔Martinelli, Agustín and Bonaparte, José. "(A new tritheledontid (Therapsida, Eucynodontia) from the Late Triassic of Rio Grande do Sul (Brazil) and its phylogenetic relationships among carnivorous non-mammalian eucynodonts )", ''Ameghiniana'', Vol. 42, p. 191 (2005).〕 The double jaw joint of ''Diarthrognathus'' neatly bridges the reptiles and mammals, and thus rebuts a claim by creationists such as Duane Gish who thought such a transition was impossible.〔Debenedictis, Albert. ''(Evolution Or Creation?: A Comparison of the Arguments )'', p. 182 (Xlibris Corporation 2011).〕〔Kitcher, Philip. ''(Abusing Science: The Case Against Creationism )'', p. 111 (MIT Press 1982).〕 This "twin-jointed jaw" can also be seen in other late cynodonts, as well as in early mammaliforms.〔Colbert, Edward and Morales, Michael. ''Evolution of the Vertebrates: A History of the Backboned Animals Through Time'', p. 228 (Wiley-Liss, 4th edition, 199) ISBN 0-471-85074-8〕 ==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「Diarthrognathus」の詳細全文を読む スポンサード リンク
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