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10-Feb-2011

Contact: Science Press Package
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American Association for the Advancement of Science

Tiny foot bone tells a walking tale



AL 333-160 left fourth metatarsal in plantar, lateral, medial, dorsal, and proximal views.
[Image courtesy of Science/AAAS]

A foot bone from the early human relative Australopithecus afarensis suggests that these hominids had stiff, arched feet, like we do, scientists have discovered.

These findings support the hypothesis that A. afarensis was primarily an upright walker, as opposed to a more versatile creature that also moved through the trees.

A. afarensis lived between 3.7 and 2.9 million years ago, and its most famous specimen is "Lucy," whose partial skeleton revealed that she walked upright. Researchers still debated, though, whether upright walking was the only way A. afarensis moved around.

A key problem has been that scientists haven't had many bones from A. afarensis' foot to study. Carol Ward of the University of Missouri and colleagues now describe a new foot bone from Hadar, Ethiopia, which they say is nearly perfectly preserved.

The bone is the fourth "metatarsal," one of the long bones connecting the toe to the base of the foot. The bone has several features similar to those of the modern human foot, and not like those of other apes.

By analyzing the shape and other details of this bone, Dr. Ward and her colleagues concluded that the A. afarensis foot had a well-formed arch. This foot should have been stiff enough to push off against the ground but also flexible enough to absorb shock –things a foot needs to be for walking.

This fossil thus suggests that A. afarensis' feet had fully transformed from grasping structures to ones used for human like walking and running on two feet, the authors say.

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These findings appear in the 11 February 2011 issue of the journal Science.