Published online 21 June 2010 | Nature | doi:10.1038/news.2010.305

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Africa's next top hominid

Ancient human relative could walk upright.

Big Man"Kadanuumuu", or Big Man, walked upright some 3.58 million years ago.Haile-Selassie Y., et al./PNAS

A hominid species made famous by the 'Lucy' fossil from Ethiopia could walk down a runway just like a fashion model today, a newly reported partial skeleton shows.

Nicknamed 'Big Man', the 3.58-million-year-old male skeleton settles a long-simmering argument over the bipedality of Australopithecus afarensis, an extinct relative of modern humans, say the authors of an article appearing online today in the Proceedings of the National Academy of Sciences1.

When Lucy, the first A. afarensis skeleton ever found, strode onto the world stage in the mid-1970s, she was estimated to be a record 3.2 million years old. Her partial skeleton set off a hot debate among anthropologists about the extent of A. afarensis's ability to walk upright.

The new skeleton comes from the Rift Valley in the central Afar of Ethiopia, about 330 kilometres northeast of Addis Ababa. Found in 2005 by a team member, Alemayehu Asfaw, the bones were located near the Mille River, a long day's walk north of Hadar where Lucy was discovered. Called Kadanuumuu, or Big Man, by the research team, the skeleton is estimated to be nearly 2 metres tall. Lucy was just over 1 metre tall.

"This new skeleton shows a fully running and walking biped, with most of the adaptations we have" says team member Owen Lovejoy, a palaeoanthropologist at Kent State University in Kent, Ohio.

"What we see in the new skeleton's pelvis is what we see in modern humans," adds lead author Yohannes Haile-Selassie, from the Cleveland Museum of Natural History in Cleveland, Ohio.

Walking tall

Lucy's small frame caused some disagreement over earlier interpretations of bipedality, Lovejoy contends, but Big Man's size and adult age allow clearer comparisons with other hominids.

The new find supports conclusions drawn last year about the even earlier bipedality of another Ethiopian hominid, Ardipithecus ramidus, which at a minimum of 4.4 million years old is the oldest hominid found so far. A. ramidus wasn't fully modern, however; it retained ape-like arms and feet, which Big Man and Lucy don't have.

But the new skeleton doesn't answer all the questions about when hominids began walking upright.

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William Jungers, of Stony Brook University in New York, who was not involved in the study, says A. afarensis, like Lucy and Big Man, were "adept and committed bipeds," but he adds, they were not "identical and biomechanically equivalent to people". In 1982, Jungers wrote that he saw Lucy as "not incompatible with some form of bipedal locomotion," but that a "bipedal gait of modern humans seems highly improbable" 2.

Carol Ward of the University of Missouri at Columbia agrees that the debate over exactly how A. afarensis walked is likely to continue.

Still, Big Man does add important information about the evolution of the upper body of hominids, she notes. The shoulder blade, or scapula, is the oldest hominid scapula discovered, and an adult one, which allows for a proper comparison to other species. The scapula, which anchors the shoulder muscles, is very similar to that of a modern human, Lovejoy says, indicating that an arboreal life like that of its ape ancestors was distant history.

And Big Man's tibia (a long bone of the lower leg) is surprisingly long, Lovejoy says. He notes that this characteristic eliminates the proposal by some researchers that later hominids evolved longer legs as an adaption enabling them to hunt over longer distances efficiently.

Big Man is the third new report of hominid remains in less than a year, which together throw light on hominid development from 4.4 to 1.9 million years ago. 

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