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Species that stood on hind limbs

As early as six million years ago, apparently close to the beginning of the human lineage, an ancestral species had already developed the transforming ability for upright walking, scientists reported on Thursday.

A new, more detailed analysis of a fossil thigh bone found eight years ago in Kenya yielded strong evidence that the species Orrorin tugensis stood and walked on its hind limbs.

The scientists said this was the earliest known example of pre-human bipedal locomotion.

The findings are described in a report in the journal Science by Brian G. Richmond and William L. Jungers, paleoanthropologists at George Washington University and the State University of New York at Stony Brook, respectively.

The research included an examination of the original fossils and a comparison with skeletons of modern humans and protohumans and also chimpanzees.

Professor Richmond said in a telephone interview that he was given access to the bones, deposited in a bank vault in Nairobi, and made his independent tests under the watchful eyes of a guard.

The size of the specimen’s hip joint, the shape and strength of the wide thigh bone, and other characteristics, he said, provided “convincing evidence to confirm Orrorin’s bipedal adaptations.”

The scientists said their analysis of hand and arm bones showed the species “most probably also climbed trees, presumably to forage, build nests and seek refuge.”

The fossils were first thought to be related more closely to the genus Homo than to Australopithecus, an intermediate genus that first emerged nearly four million years ago and included species living as recently as two million years ago.

This seemed to make Orrorins a more direct human ancestor, possibly relegating “Lucy” and other australopithecines to a side branch of the family tree. — AP

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