A publication of the Archaeological Institute of America
A new study of a fossil thigh bone shows that walking upright may have already been old hat six million years ago. Researchers led by Penn State anthropologist Robert Eckhardt analyzed CAT scans of a fragment of the left femur of Orrorin tugenensis, a chimpanzee-size creature whose place on the hominid family tree has been the subject of controversy since its discovery in the hills of western Kenya nearly four years ago ("Ancient Ancestors?" July/August 2001). According to Eckhardt, the CAT scans reveal the internal structure of the bone "is considerably closer to an upright bipedal human than to a chimpanzee," suggesting that Orrorin walked on two feet.
"We don't know what Orrorin looked like," says Eckhardt. "We don't have a crystal ball. But by the time you see structural changes in the bones like this, there has been some behavioral change. This is solid evidence for bipedalism, dated to six million years ago." The new analysis bolsters the case that Orrorin is an ancestral hominid, but other researchers point to features like Orrorin's teeth, which are more apelike, as evidence that the species may be more closely related to chimpanzees.