Fossil discovery could unravel mystery of how humans learned to walk (+video)

The fossils include eight bones from the front half of a right foot. Such hominin fossils are rare, since they are fragile and subject to decay or carnivores.

While the big toe of Lucy's species was lined up with the other four toes to make humanlike walking more efficient, the Burtele foot has an opposable big toe like a gorilla's. This probably made the species more adept than Lucy's at grasping branches and climbing trees.

The Burtele foot, however, does bear hints that it could have been used for upright walking. For instance, several bones have large, spherical features that suggest the hominin could hyperextend its toes to help the body push forward and upward. Still, unlike in Australopithecus and humans, the foot lacked an arch, an energy-absorbing feature of feet that helps protect bones.

"It wasn't walking great distances on the ground," Latimer said. "It would've had a quite awkward gait."

Project leader Yohannes Haile-Selassie, curator and head of physical anthropology at the Cleveland Museum of Natural History, said the researchers hope to uncover more fossil specimens of this unknown hominin, including its head and teeth, to help pinpoint what species it might be.

"This new discovery will definitely raise new questions and controversies as to how we understand the evolution of bipedality in the human lineage," Haile-Selassie told LiveScience.

The Burtele foot resembles that of another hominin, "Ardi," which lived 4.4 million years ago. It could be that Ardi – short for Ardipithecus ramidus – is the forerunner of both the Burtele hominin and Australopithecus, Haile-Selassie said.

The scientists detail their findings in the March 29 issue of the journal Nature.

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