Orrorin tugenensis

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iOrrorin
Fossil range: Miocene

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Primates
Family:	Hominidae
Subfamily:	Homininae
Tribe:	Hominini
Subtribe:	Hominina
Genus:	Orrorin Senut et al, 2001
Species:	O. tugenensis

Binomial name

†Orrorin tugenensis
Senut et al, 2001

Orrorin tugenensis is considered as the second oldest possible hominin ancestor related to modern humans (the oldest being Sahelanthropus tchadensis) and is the only species classified in genus Orrorin. The name was given by the discoverers who found Orrorin fossils near the village of Tugen, Kenya. By using radiometric dating techniques, the volcanic tuffs where the fossils were found date to between 6.1 and 5.8 million years ago, during the Miocene. The fossils found so far come from at least five individuals. They include a femur, suggesting that Orrorin walked upright; a thick right humerus, suggestive of tree-climbing skills but not brachiation; and teeth that suggest a diet much like that of modern humans. The full 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. Pickford claims that Orrorin is clearly a hominin; based on this, he dates the split between hominins and other African great apes to at least 7 million years ago. This date is markedly different from those derived using the molecular clock approach.

If Orrorin proves to be a direct human ancestor, the australopithecines such as Australopithecus afarensis ("Lucy") may be considered a side branch of the hominid family tree: Orrorin is both earlier, by over 1.5 million years, and more similar to us than A. afarensis. The main similarity is that the Orrorin humerus seem closer to H. sapiens in comparison to Lucy's; there is, however, significant controversy over this point, and other researchers assert that Pickford et al. gloss over a number of uncertainties. Other fossils found in these rocks show that Orrorin lived in a wooded environment, not the savanna assumed by many theories of human evolution and, in particular, the origins of bipedalism.

[edit] References

B. Senut, M. Pickford, D. Gommery, P. Mein, K. Cheboi, and Y. Coppens, "First hominid from the Miocene (Lukeino Formation, Kenya)". Comptes Rendus de l'Académie de Sciences, vol. 332, pp. 137-144, 2001.
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