Orrorin tugenensis

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Orrorin tugenensis is considered to be the second-oldest (after Sahelanthropus) known hominin ancestor that is possibly related to modern humans, and it is the only species classified in genus Orrorin. Orrorin is significant because it can be an early bipedal hominin.

The name[1] was given by the discoverers who found Orrorin fossils in the Tugen Hills of Kenya. [2] By analysing radiometric decay (K–Ar dating), paleomagnetism, and biochronology the age of the specimen have been estimated to 6 to 5.8 million years (Ma) (average: 6.1 Ma). At present, 20 fossils have been found at four sites in the Lukeino Formation: of these, the fossils at Cheboit and Aragai are the oldest (6.1 Ma), while those in Kapsomin and Kapcheberek are found in the upper levels of the formation (5.7 Ma). [3]

Contents

Fossils

The 20 specimen found this far include: the posterior part of mandible in two pieces; a symphysis and several isolated teeth; three fragments of femurs; a partial humerus; a proximal phalanx; and a distal thumb phalanx. [3]

Orrorin had small teeth relative 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 Australopithecus was megadont. [3]

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