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Thursday, October 1, 2009

4.4 million-year-old hominid skeleton 'Ardi' discovered in Ethiopia



The fossil, known as 'Ardi', is the oldest specimen on the hominid branch that led to modern humans yet unearthed
Hannah Devlin 5 Comments
Recommend? (5) The discovery of a 4.4 million-year-old skeleton in Ethiopia has allowed scientists to retrace the first evolutionary steps of our ancestors after they split away from those of modern chimpanzees.

The fossil reveals our earliest predecessor to have been a stocky, stooping creature, covered in hair, with a protruding face, long arms and a grasping big toe.

The fossil, known as “Ardi”, is the oldest specimen on the “hominid” branch that led to modern humans yet unearthed. It is more than 1 million years older than the famous “Lucy” skeleton.

Quoting Charles Darwin, Dr Tim White, the paleoanthropologist who led the original “Lucy” investigation, said: “The only way we’re really going to know what this last common ancestor looked like is to go and find it.”

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At 4.4 million years old, the Ardi fossil is the closest specimen yet to that common ancestor. It possesses a strange mosaic of human and chimpanzee traits, combined in ways that scientists say they would never have been able to guess by simply triangulating between the modern versions of the two species.

Ardi has a relatively small skull, suggesting a comparable level of intellect to modern chimps. The angle of her head relative to her spine shows that she would have been able to walk upright in a stooped posture. However, she retains the “grasping” big toe of our more primitive ancestors, as well as long arms and big hands, which point to her being an able climber. Unlike chimpanzees and orangutans, though, she would not have been able to swing through the trees.

The almost complete skeleton of Ardipithecus ramidus was scattered in hundreds of pieces in volcanic ash in Afar, which lies in the Great Rift Valley in northeastern Ethiopia.

The skeleton was excavated bone by bone by Ethiopian and American scientists between 1994 and 1996.

It has taken almost 15 years for scientists to piece together and analyse the specimen. In 11 separate articles published tomorrow in the journal Science, a team of 47 scientists describe and interpret in exquisite detail the skeleton and its implications for our understanding of where we come from.

The fossil has prompted scientists to recast their thinking on the evolution of chimpanzees. The assumption of many had been that chimpanzees had undergone much less evolution than the human line. “A lot of people predicted that when you found something at 4.4 million years ago, it would look like a chimp,” said Dr White.

However, “Ardi” suggests that our last common ancestor was as remote from chimpanzees as it was from humans.

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