LOS ANGELES — With long arms, high shoulder blades and powerful fingers, the ancient creatures were built for climbing trees. But they also had long lower limbs, flat feet and a flexible lumbar spine that gave them a distinct evolutionary edge: They could cover long distances by walking upright on two legs.
After four years of intense analysis, a team of paleoanthropologists makes a detailed case that a pair of ancient skeletons discovered in a grassy South African valley could represent the direct evolutionary link between modern humans and the family of human ancestors that includes the Australopithecus known as Lucy.
In a series of six papers published in today's edition of the journal Science, the researchers argue that the "mosaic nature" of the Australopithecus sediba specimens makes them a strong candidate to be the "missing link" — the branch of Australopithecus that gave rise to the genus Homo, which includes Homo sapiens.
The skeleton fossils have so many human-like features "across the whole of the body that it must be considered, at the very least, a possible ancestor," said Lee R. Berger, a paleoanthropologist at the University of Witwatersrand in Johannesburg, South Africa, who discovered the fossils in 2008. Berger was senior author of all the new studies.
But not everyone accepts this view. Critics say the skeletons are not old enough to be the precursors to Homo. Others say the similarities can be chalked up to the diversity of early hominids, but that certain aspects of A. sediba's anatomy make it an unlikely candidate for being our forebear.