The fossil foot found in the Afar region of Ethiopia did not belong to a member of "Lucy's" species, Australopithecus afarensis, the most famous early human ancestor, researchers with the Cleveland Museum of Natural History said Wednesday.
The discovery suggests more than one species of early human ancestor existed between 3 and 4 million years ago with different methods of locomotion, a museum release reported.
The fossil foot was found in February 2009 in an area known as Burtele.
"The Burtele partial foot clearly shows that at 3.4 million years ago, Lucy's species, which walked upright on two legs, was not the only hominin species living in this region of Ethiopia," Yohannes Haile-Selassie, the museum's curator of physical anthropology, said.
"Her species co-existed with close relatives who were more adept at climbing trees, like 'Ardi's' species, Ardipithecus ramidus, which lived 4.4 million years ago."
While the big toe of the foot in Lucy's species was aligned with the other four toes for human-like bipedal walking, Haile-Selassie said, the Burtele foot has an opposable big toe like the earlier Ardi.
"These fossil elements represent bones we've never seen before," study co-author Bruce Latimer of Case Western Reserve University said.
"While the grasping big toe could move from side to side, there was no expansion on top of the joint that would allow for expanded range of movement required for pushing off the ground for upright walking," he said.
"This individual would have likely had a somewhat awkward gait when on the ground."
The new partial foot specimen has not yet been assigned to a species due to the lack of associated skull or dental elements, the researchers said.