A foot bone from the early human relative Australopithecus afarensis suggests that these hominids had stiff, arched feet, like we do. 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.
This research appears in the 11 February issue of the journal Science, which is published by AAAS, the nonprofit science society.
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 have long debated over the actual extent to which A. afarensis was bipedal, however, and their understanding has been hampered by a sparse fossil record lacking key bones from A. afarensis' midfoot.
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 a complete 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, as opposed to those of other apes. For example, its two ends are twisted in relation to each other, and it slopes at a relatively sharp angle from the foot base to the toe.
This foot, with its well-formed arch, should have been stiff enough to push off against the ground but also flexible enough to absorb shock. This fossil thus suggests that A. afarensis' feet had fully transformed from grasping structures to ones facilitating human like walking and running on two feet, the researchers say.
This research was supported by the National Science Foundation, the University of Missouri Research Board, the University of Missouri Research Council and the Institute of Human Origins at Arizona State University.
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