New research suggests that the footprints that were found in the 1970s may have been left by an early human.
Two years after the discovery of the footprints near the site at Laetoli, Mary Leakey and her team found another set of prints that are believed to have been made by the same species that left behind theLucy skeleton.
The prints were overshadowed. The prints had largely been forgotten by archaeologists until now, after a paleoanthropologist suggested they could have been bear tracks.
A new analysis of those prints, published in the journal Nature on Wednesday, indicates that they were made by an early human. The findings show that Lucy's species was not the only hominin that existed 3.6 million years ago.
Jeremy De Silva, an associate professor of anthropology at Dartmouth and a senior author of the study, said that right walking is a defining characteristic of our lineage. It is a hallmark of being a human. Our understanding of the origins and evolution of bipedal locomotion is something we are still trying to figure out.
The lead author of the study was an assistant professor at the Heritage College of Osteopathic Medicine at Ohio University. She came across a set of five footprints that had been partially excavated in 1976, and thought they could help untangle the mystery of what led humans to walk on two legs.
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Two years later, a print that is believed to have been made by the same species that left behind the famousLucy skeleton, was found.
The A trail was an unusual shape, like a shorter and more stout version of a modern human's footprint. They showed a cross-step walking movement in which each foot crosses the body's midline to touch down in front of the other.
The researchers said that the prints were made by a different species than Lucy's, one that did not share an evolutionary trajectory with Chimpanzees. The researchers said that the foot is wider than a typical early human and that the cross-walk pattern that the prints show can only happen if a species walks on two legs.
The researchers recorded over 60 hours of video. They said that supported bipedal posture and movement occurred less than 0.10 percent of the time. The study shows that a bear only took four unassisted steps. The archaeologists concluded that it was unlikely that the prints belonged to a bear.
Having more than one hominin species living during the same time period, walking a little differently with different foot sizes, tells us that there wasn't a one-track way to our evolution. The kind of way that we do is the only one that is still alive today.
The study comes as more research is challenging and changing the understanding of how many early human species occupied the earth three million to 3.7 million years ago. Dr. Melillo summarized the findings for Nature.
Both sets of footprints could have been made within days of each other, according to William Harcourt-Smith, an associate professor of anthropology at Lehman College and a resident research associate at the American Museum of Natural History.
Dr. Harcourt-Smith said that the footprints were made in almost exactly the same time.
He said this is the real deal. It is the smoking gun of two different fossil hominins at the same time in the same landscape, if they are indeed both hominins.
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The lead author of the new study was Ellison McNutt. A footprint from a black bear.
Tim D. White, a paleoanthropologist and a professor at the University of California, Berkeley, was not convinced that a new hominin species had been identified.
The differences between the footprints in Laetoli were not enough to prove the existence of another bipedal species, according to Dr. White. When footprints are made in volcanic ash, the prints at their deeper layers can change in size and shape.
The experts agreed that the new research proves that the A trail prints were not made by bears. There are no bears in the fossil record.
The researchers said they would continue to dig in order to find more footprints.
