“They are unable to walk with a gait similar to that of the Site A footprints, as their hip musculature and knee shape does not permit that kind of motion and balance.” Bear heels taper and their toes and feet are fan-like, while early human feet are squared off and have a prominent big toe, according to the researchers. 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.Īs bears walk, they take very wide steps, wobbling back and forth,” says senior author Jeremy DeSilva, an associate professor of anthropology at Dartmouth. Over 50 hours of video on wild black bears was also obtained. 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. They identified four semi-wild juvenile black bears at the Center, with feet similar in size to that of the Site A footprints. 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. On right: Left footprint from one of the juvenile male black bears. On left: Ellison McNutt collects data from a juvenile female black bear (Ursus americanus), who walks bipedally, unassisted through the mud trackway at Kilham Bear Center in Lyme, New Hampshire. The researchers compared the Laetoli Site A tracks to the footprints of black bears ( Ursus americanus), chimpanzees ( Pan troglodytes), and humans (Homo sapiens). The footprints were measured, photographed and 3D-scanned. They identified evidence that the fossil footprints were made by a hominin-including a large impression for the heel and the big toe. 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. 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. McNutt was fascinated by the bipedal (upright walking) footprints at Laetoli Site A. Credit: Image on left by Jeremy DeSilva and on right by Eli Burakian/Dartmouth Analysis shows similarities in length of Laetoli A3 and G footprints but differences in forefoot width with the former being wider. Image of Laetoli A3 footprint (on left) and image of a cast of Laetoli G1 footprint (on right). 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”).
“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. 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. Another set of mysterious footprints was partially excavated at nearby Site A in 1976 but dismissed as possibly being made by a bear. The bipedal trackways date to 3.7 million 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. Images (d) and (e) by Stephen Gaughan and James Adamsįindings provide conclusive evidence that multiple species of hominins co-existed on the landscape.
Image (c): Illustration using GoogleMaps by Ellison McNutt. Model of Laetoli Site A using photogrammetry showing five hominin footprints (a) and corresponding contour map of the site at Laetoli, Tanzania, generated from a 3D surface scan (b) map showing Laetoli, which is located within the Ngorongoro Conservation Area in northern Tanzania, south of Olduvai Gorge (c) topographical maps of A2 footprint (d) and A3 footprint (e).
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