Unearthed fossil foot could belong to new human ancestor, scientists say

Ancient foot bones discovered in Ethiopia point to the existence of a previously-unknown human ancestor whose feet were specially adapted to tree climbing.

U.S. and Ethiopian scientists said that a 3.4 million-year-old partial foot found in Burtele, in the remote Afar region of Ethiopia, belonged to a prehuman who coexisted with the famous "Lucy" species, Australopithecus afarensis.

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Scientists have long argued that there was only one prehuman species between three and four million years ago, but the fossilized foot bones provide the first indisputable evidence that at least two prehuman species with different modes of movement lived at the same time in East Africa.

The discovery, detailed Thursday in the journal Nature, suggests that while the newly-discovered species could walk upright like members of the "Lucy" species, its opposable big toe meant it was more adept at climbing and swinging from trees.

Researchers hope the fossils will provide scientists with a clearer picture of how primitive feet evolved and humans became separated from apes.

"It is now clear that the adaptation to terrestrial bipedality was not a single, isolated event," coauthor Bruce Latimer of Case Western Reserve University in Cleveland said.

He added, "Rather, one group [Lucy's species] totally relinquished the arboreal habitat and became functionally-committed, long-distance ground walkers -- while another group, represented by the Burtele foot, maintained a climbing foot and stayed, at least part of the time, in the trees. It is now apparent which group succeeded."

The new Burtele species cannot be named until a skull and teeth are found, the scientists said.