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''Orrorin tugenensis'' is a postulated early species of Homininae, estimated at and discovered in 2000. It is not confirmed how ''Orrorin'' is related to modern humans. Its discovery was an argument against the hypothesis that australopithecines are human ancestors, as much as it still remains the most prevalent hypothesis of human evolution as of 2012. The name of genus ''Orrorin'' (plural ''Orroriek'') means "original man" in Tugen, and the name of the only classified species, ''O. tugenensis'', derives from Tugen Hills in Kenya, where the first fossil was found in 2000.〔 As of 2007, 20 fossils of the species have been found. ==Fossils== The 20 specimens found as of 2007 include: the posterior part of a mandible in two pieces; a symphysis and several isolated teeth; three fragments of femora; a partial humerus; a proximal phalanx; and a distal thumb phalanx. 〔 ''Orrorin'' had small teeth relative to its body size. Its dentition differs from that found in ''Australopithecus'' in that its cheek teeth are smaller and less elongated mesiodistally and from ''Ardipithecus'' in that its enamel is thicker. The dentition differs from both these species in the presence of mesial groove on the upper canines. The canines are ape-like but reduced, like those found in Miocene apes and female chimpanzees. ''Orrorin'' had small post-canines and was microdont like modern humans, whereas robust ''Australopithecenes'' were megadont. 〔 In the femur, the head is spherical and rotated anteriorly; the neck is elongated and oval in section and the lesser trochanter protrudes medially. While this suggest that ''Orrorin'' was bipedal, the rest of the postcranium indicates it climbed trees. While the proximal phalanx is curved, the distal pollical phalanx is of human proportions and has thus been associated with toolmaking, but should probably be associated with grasping abilities useful for tree-climbing in this context.〔 After the fossils were found in 2000, they were held at the Kipsaraman village community museum, but the museum was subsequently closed. Since then, according to the Community Museums of Kenya chairman Eustace Kitonga, the fossils are stored at a secret bank vault in Nairobi. 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「Orrorin」の詳細全文を読む スポンサード リンク
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