The fourth metatarsal of the Burtele partial foot right after discovery in Stephanie Melillo's hand.Yohannes Haile-Selassie / The Cleveland Museum of Natural History
A laboratory photo shows the Burtele partial foot (BRT-VP-2/73) in its anatomically articulated form after cleaning and preparation.Yohannes Haile-Selassie / The Cleveland Museum of Natural History
The first element of the Burtele partial foot, fourth metatarsal, as it was found on the ground in the Woranso-Mille area of the Afar region of Ethiopia.Yohannes Haile-Selassie / The Cleveland Museum of Natural History
Lead author Dr. Yohannes Haile-Selassie, curator of physical anthropology at The Cleveland Museum of Natural History, in the field investigating a fossil fragment.Yohannes Haile-Selassie / The Cleveland Museum of Natural History
The Burtele partial foot embedded in an outline of a gorilla foot.Yohannes Haile-Selassie / The Cleveland Museum of Natural History
CLEVELAND – 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.
'One group became long-distance ground walkers, while another group stayed in the trees. It is now apparent which group succeeded.'
- coauthor Bruce Latimer of Case Western Reserve University
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.