An international team of Ethiopian and American scientists conducting paleontological field research in the Woranso-Mille area of the Afar region of Ethiopia has discovered a partial foot skeleton, which is the first fossil evidence to show the presence of more than one pre-human species in eastern Africa at the beginning of the Late Pliocene epoch.
The 3.4-million-year-old partial foot was found in February 2009 in an area locally known as Burtele.
In the study, published today in the journal Nature, the team says that the fossil did not belong to a member of “Lucy’s” species, Australopithecus afarensis, the famous early human ancestor found in this location and from the same period.
While the big toe of the foot in Lucy’s species was aligned with the other four toes for human-like bipedal walking, the Burtele foot has an opposable big toe like the earlier Ardipithecus ramidus.
“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,” said Dr. Yohannes Haile-Selassie, a lead author and a curator of physical anthropology at the Cleveland Museum of Natural History. ”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.”
The scientists suggest that the new partial foot specimen is the first evidence for the presence of at least two pre-human species with different modes of locomotion contemporaneously living in eastern Africa about 3.4 million years ago.
“This discovery was quite shocking,” said Dr. Bruce Latimer of Case Western Reserve University, a co-author on the study. “These fossil elements represent bones we’ve never seen before. 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. This individual would have likely had a somewhat awkward gait when on the ground.”
The specimen has not yet been assigned to a species due to the lack of associated skull or dental elements.
“The fossils were found below a sandstone layer,” said study co-author Dr. Beverly Saylor of Case Western Reserve University. “Using the argon-argon radioactive dating method, their age was determined to be younger than 3.46 million years.”
“Nearby fossils of fish, crocodiles and turtles, and physical and chemical characteristics of sediments show the environment was a mosaic of river and delta channels adjacent to an open woodland of trees and bushes. This fits with the fossil, which strongly indicates a hominin adapted to living in trees, at the same time ‘Lucy’ was living on land.”