Once Believed to Have Came from Bears, Footprints in Archeological Site Found to Have Belonged to Early Humans

Footprints discovered by paleontologist Mary Leakey and her colleagues in Laetoli, Tanzania, in 1978 are the oldest unambiguous evidence of upright walking in the human lineage. The bipedal trackways may be traced back 3.7 million years. In 1976, another pair of strange footprints was partially unearthed at adjacent Site A, but they were disregarded as bear tracks. According to a new study published in Nature, a recent re-excavation of the Site A footprints at Laetoli and a rigorous comparative analysis suggest that the footprints were created by an early human - a bipedal hominid.

Discovering Footprints in the 70s

The bipedal (upright walking) footprints at Laetoli Site A piqued McNutt's interest. Laetoli is known 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 the footprints at Site A were so different that some researchers thought they were made by a young bear walking upright on its hind

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Revisiting the Discovery

In June 2019, an international research team led by co-author Charles Musiba, an associate professor of anthropology at the University of Colorado Denver, traveled to Laetoli to re-excavated and thoroughly cleaned the five successive footprints to discover who made them. They found indications that the fossil footprints were formed by a hominin, including a massive heel and enormous toe imprint. The prints were scanned in 3D, photographed, and measured.

The Laetoli Site A footprints were compared to those of black bears (Ursus americanus), chimps (Pan troglodytes), and humans (Homo sapiens).

They collaborated with co-authors Ben and Phoebe Kilham, who manage the Kilham Bear Center in Lyme, New Hampshire, specializing in black bear rescue and rehabilitation. At the Center, they found four semi-wild adolescent black bears with feet identical in size to the Site A footprints. Each bear was enticed to rise and walk on its hind legs through a mud-filled trackway to record its footprints with maple syrup or apple sauce.

Comparing Footprints

"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," says senior author Jeremy DeSilva, an associate professor of anthropology at Dartmouth. "Their hip musculature and knee shape do 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

"Although humans don't generally cross-step, this action can occur when one is trying to regain their equilibrium," McNutt adds. "The Site A footprints could have been the consequence of a hominin traveling across an unlevel surface."

The study discovered that chimps have relatively thin heels than their forefoot, a characteristic shared with bears, based on footprints gathered from semi-wild chimps at Ngamba Island Chimpanzee Sanctuary in Uganda and two captive adolescents at Stony Brook University. However, Laetoli footprints, including those found at Site A, have broad heels compared to their forefoot.

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