Two fossils from Ethiopia offer new evidence for upright walking in early human ancestors. The findings may give further clues to how bipedalism evolved.
Ever since the 3.1-million-year-old skeleton of Lucy was unearthed in Ethiopia 30 years ago, paleoanthropologists have wondered when and how her ancestors began walking upright. Lucy was the first to establish that hominids began walking upright well before their brains expanded, prompting new questions about what caused human ancestors to become bipedal.
New clues are sure to come from a specimen that predates Lucy and lived 3.8 million to 4 million years ago. This well-preserved partial skeleton was discovered in February near the village of Mille in the badlands of Ethiopia by Ethiopian paleoanthropologist Yohannes Haile-Selassie of the Cleveland Museum of Natural History (Science, 11 March 2005, p. 1545). The shape of the pelvis and the top of the shinbone show that this early ancestor was definitely walking upright, the researchers say.
Another team, led by Horst Seidler of the University of Vienna (UV), announced the discovery of a second fossil this winter: a 3.8-million- to 4.5-million-year-old partial thighbone found by UV graduate student Bence Viola about 100 kilometers south of Mille at a site called Galili. The thighbone likewise reveals an individual who walked upright. But a preliminary assessment indicates that muscles and ligaments would have attached to the bone differently from in Lucy's species, Australopithecus afarensis, suggesting another type of walk, says anthropologist Gerhard Weber of the University of Vienna. But as the thighbone is reconstructed from 26 fragments, its gait may be tough to reconstruct, comments Owen Lovejoy, an anatomist at Kent State University in Kent, Ohio.
These new fossils should provide hard evidence to a scanty fossil record for the lower limbs of hominids that walked upright more than 4 million years ago. Only two other legbones and one toebone have been published to show that fossils older than these new discoveries walked upright as early as 6 million years ago. A mysterious 4.4-million-year-old partial skeleton was discovered in 1996 in Ethiopia and is expected to be the Rosetta stone for understanding the evolution of upright walking, but it is unpublished and remains under study. Still, Weber notes that the gap in the fossil record is beginning to fill--and may finally give paleoanthropologists a leg to stand on as they explain the evolution of bipedalism.