A tiny 3.2-million-year-old fossil found in East Africa gives Lucy’s kind an unprecedented toehold on humanlike walking.
Australopithecus afarensis, an ancient hominid species best known for a partial female skeleton called Lucy, had stiff foot arches like those of people today, say anthropologist Carol Ward of the University of Missouri in Columbia and her colleagues. A bone from the fourth toe — the first such A. afarensis fossil unearthed — provides crucial evidence that bends in this species’ feet supported and cushioned a two-legged stride, the scientists report in the Feb. 11 Science.
“We now have the evidence we’ve been lacking that A. afarensis had fully developed, permanent arches in its feet,” Ward says. Survival for Lucy and her comrades must have hinged on abandoning trees for a ground-based lifestyle, she proposes.
The new fossil confirms that members of Lucy’s species could have made 3.6-million-year-old footprints previously found in hardened volcanic ash at Laetoli, Tanzania (SN Online: 3/22/10), she says. A. afarensis lived from about 4 million to 3 million years ago.
Scientists have argued for more than 30 years about whether Lucy and her kin mainly strode across the landscape or split time between walking and tree climbing.
News of arched feet in these hominids comes on the heels of a report that a recently discovered A. afarensis skeleton, dubbed Big Man, displays long legs, a relatively narrow chest and an inwardly curving back, signs of a nearly humanlike gait (SN: 7/17/10, p. 5).
“There were far too many highly detailed adaptations in every part of the A. afarensis skeleton for upright walking and exclusive ground travel not to have emerged,” remarks anthropologist Owen Lovejoy of Kent State University in Ohio, who studied Big Man’s remains.
A foot much like that attributed to Lucy’s kind by Ward’s group had already evolved by 4.4 million years ago in the early hominid Ardipithecus (SN: 1/16/10, p. 22), Lovejoy says. Although Ardipithecus had an opposable big toe incapable of propelling a two-legged gait, this creature walked effectively using its other toes, in his view.
Based on the new find, A. afarensis does appear to have had arched feet, remarks anthropologist William Jungers of Stony Brook University School of Medicine in New York. But other foot features, including long, curved fifth toes, indicate that a skeletal system for upright walking had not fully evolved in Lucy’s kind, Jungers asserts.
Considerable differences in foot anatomy may have existed among members of A. afarensis, Jungers says. An analysis of fossil ankle bones published in 2010 by other researchers concluded that Lucy had flat feet while many of her comrades had an arch at the back of the foot.
“Even if Lucy had lower arches than other individuals, she still would have had the stiff, humanlike foot structure that we see in people but not in apes,” Ward says.
Excavations at one of several sites at Hadar, Ethiopia, yielded the ancient toe bone in 2000. Since 1975, this location has produced more than 250 fossils representing at least 17 A. afarensis individuals.
Shape and design features of the fossil toe closely match those of corresponding toes on people but not chimpanzees or gorillas, Ward’s team says.