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''Thrinaxodon'' is an extinct genus of cynodont, most commonly regarded by its species ''T. liorhinus'' which lived in what are now South Africa and Antarctica. ''Thrinaxodon'' has been dated between the Permian and mid-Triassic periods, indicating that it was one of the few species to survive the Permian mass extinction. Its survival may have been due to its burrowing habits. Similar to other synapsids, ''Thrinaxodon'' adopted a semi-sprawling posture, an intermediary form between the sprawling position of pelycosaurs (not unlike current Crocodylia) and the more upright posture present in current mammals.〔Blob R. 2001. Evolution of hindlimb posture in non-mammalian therapsids: biomechanical tests of paleontological hypotheses. 27(1): 14-38.〕 ''Thrinaxodon'' is prevalent in the fossil record due in part to that fact that it was one of the few carnivores of its time, and was of a larger size than similar cynodont carnivores.〔''Thrinaxodon''. (n.d.). Retrieved March 5, 2015, from http://www.prehistoric-wildlife.com/species/t/thrinaxodon.html〕 It was a small synapsid ranging in size between 30 cm and 50 cm. ==Description== ''Thrinaxodon'' was a small synapsid roughly the size of a fox〔 with hair presumably growing between its scales. The dentition suggests that it was a carnivore, focusing its diet mostly on insects, small herbivores and invertebrates. Their unique secondary palate successfully separated the nasal passages from the rest of the mouth, allowing the ''Thrinaxodon'' to continue mastication without interrupting to breathe, an adaptation important for digestion.〔 The bone histology of ''Thrinaxodon'' indicates that it most likely had very rapid bone growth during juvenile development, and much slower development throughout adulthood, giving rise to the idea that ''Thrinaxodon'' reached peak size very early in its life.〔Botha J. Chinsamy A. 2005. Growth patterns of ''Thrinaxodon'' ''liorhinus'', a non-mammalian cynodont from the lower Triassic of South Africa. Paleontology. 48(2): 385-394.〕 ''Thrinaxodon'' has been identified as a burrowing cynodont by numerous discoveries in preserved burrow hollows. There is evidence that the burrows are in fact built by the ''Thrinaxodon'' to live in them, and they do not simply inhabit leftover burrows by other creatures. Pitted foramina on the snout of ''Thrinaxodon'' indicate the likely presence of the sensory organ, whiskers, an adaptation likely used to assist navigation and sensation within burrows. Due to the evolution of a segmented vertebral column into thoracic, lumbar and sacral vertebrae, ''Thrinaxodon'' was able to achieve flexibilities that permitted it to comfortably rest within smaller burrows, which may have led to habits such as aestivation or torpor. This evolution of a segmented rib cage suggests that this may have been the first instance of a diaphragm in the synapsid fossil record; however, without the proper soft tissue impressions this is nothing more than an assumption.〔〔Brink A. Note on a new skeleton of ''Thrinaxodon'' ''liorhinus''. Abstract. 15-22.〕〔Damiani R. Modesto S. Yates A. Neveling J. Earliest evidence of cynodont burrowing. 2003. The Royal Society. 1747-1751.〕 Current fossil evidence restricts the geographic location of ''T. liorhinus'' to South Africa and Antarctica. The discovery of ''T. liorhinus'' in these incredibly separated land masses has been used as evidentiary support that Africa and Antarctica were linked land masses during the late Permian and early Triassic.〔Colbert E. Kitching J. 1977. Triassic Cynodont Reptiles from Antarctica. American Museum Novitates. 2611. 1-30.〕 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「Thrinaxodon」の詳細全文を読む スポンサード リンク
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