Footprints From Tanzania Are Those Of Early Humans 3.7M Years Ago

The oldest unequivocal evidence of upright walking in the human lineage are footprints discovered at Laetoli, Tanzania in 1978, by paleontologist Mary Leakey and her team. The bipedal trackways date to 3.7 million years ago, ScienceDaily reported.

Photo Insert: Replica of Laetoli footprints

Another set of mysterious footprints was partially excavated at nearby Site A in 1976 but dismissed as possibly being made by a bear. A recent re-excavation of the Site A footprints at Laetoli and a detailed comparative analysis reveal that the footprints were made by an early human -- a bipedal hominin, according to a new study reported in Nature.

"Given the increasing evidence for locomotor and species diversity in the hominin fossil record over the past 30 years, these unusual prints deserved another look," says lead author Ellison McNutt, an assistant professor of instruction at the Heritage College of Osteopathic Medicine at Ohio University.

She started the work as a graduate student in Ecology, Evolution, Environment, and Society at Dartmouth College, where she focused on the biomechanics of walking in early humans and utilized comparative anatomy, including that of bears, to understand how the heel bone contacts the ground (a foot position called "plantigrady").

McNutt was fascinated by the bipedal (upright walking) footprints at Laetoli Site A. Laetoli is famous for its impressive trackway of hominin footprints at Sites G and S, which are generally accepted as Australopithecus afarensis -- the species of the famous partial skeleton "Lucy."

But because the footprints at Site A were so different, some researchers thought they were made by a young bear walking upright on its hind legs. To determine the maker of the Site A footprints, in June 2019, an international research team led by co-author Charles Musiba, an associate professor of anthropology at University of Colorado Denver, went to Laetoli, where they re-excavated and fully cleaned the five, consecutive footprints.

They identified evidence that the fossil footprints were made by a hominin -- including a large impression for the heel and the big toe. The footprints were measured, photographed, and 3D-scanned.

The researchers compared the Laetoli Site A tracks to the footprints of black bears (Ursus americanus), chimpanzees (Pan troglodytes), and humans (Homo sapiens). They teamed up with co-authors Ben and Phoebe Kilham, who run the Kilham Bear Center, a rescue and rehabilitation center for black bears in Lyme, New Hampshire.

They identified four semi-wild juvenile black bears at the Center, with feet similar in size to that of the Site A footprints. Each bear was lured with maple syrup or apple sauce, to stand up and walk on their two hind legs across a trackway filled with mud to capture their footprints.

Over 50 hours of video on wild black bears was also obtained. The bears walked on two feet less than 1% of the total observation time making it unlikely that a bear made the footprints at Laetoli, especially given that no footprints were found of this individual walking on four legs.

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