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( Orrorin tugenensis)
Orrorin tugenensis is considered to be the oldest known hominin ancestor related to modern humans and is the only species classified in genus Orrorin. The name was given by the discoverers who found Orrorin fossils in the Tugen Hills of Kenya. By using radiometric dating techniques, the volcanic tuffs and lavas, faunal correlation and magneto-stratigraphy, the strata in which the fossils were found were estimated to date between 6.1 and 5.8 million years ago, during the Miocene. This find is significant because it represents the earliest hominid species with evidence of bipedal locomotion. The fossils found so far come from at least five individuals. They include a femur, suggesting that Orrorin walked upright; a right humerus shaft, suggestive of tree-climbing skills but not brachiation; and teeth that suggest a diet much like that of modern humans. The fact that the fossil Orrorin tugenensis possesses the obturator externus groove on the posterior aspect of the neck of the femur suggests that it moved bipedally. The bunodont, microdont molars and small canines suggest that Orrorin ate mostly fruit and vegetables, with occasional meat. Orrorin was about the size of a modern chimpanzee. The team that found these fossils in 2000 was led by Martin Pickford and Brigitte Senut. The discovers conclude that Orrorin is a hominin on the basis of its bipedal locomotion and dental anatomy; based on this, they date the split between hominins and African great apes to at least 7 million years ago. This date is markedly different from those derived using the molecular clock approach, but has found general acceptance among paleoanthropologists. If Orrorin proves to be a direct human ancestor, then australopithecines such as Australopithecus afarensis ("Lucy") may be considered a side branch of the hominid family tree Orrorin is both earlier, by almost 3 million years, and more similar to us than is A. afarensis. The main similarity is that the Orrorin femur is morphologically closer to that of H. sapiens than is Lucy's; there is, however, some discussion over this point.
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