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Tanzania Footprints Hint at Origin of Humans Walking Upright
By Thomas Kissel
A replica of the footprints found in Tanzania. Credit: James St. John, CC BY 2.0
A recent study shows that prehistoric footprints found in Tanzania may hold the key to understanding how early humans began walking upright.
The footprints, which were fossilized in volcanic ash 3.66 million years ago, are shedding new light on the evolution of human beings into walking creatures, with researchers noting that the tracks have a unique stride.
The tracks were first discovered nearly fifty years ago in 1976 at a site known as Laetoli in northern Tanzania. They were initially believed to have been left by bears, but this new study has determined that they were actually from two hominin species.
The trackway discovery was on the heels of the discovery of another set of footprints in 1978, which were immediately attributed to the Australopithecus afarensis species. Experts were wary about recognizing the tracks from Laetoli as human because they were so different than the ones found in 1978.
Paleoanthropologist Ellie McNutt of Ohio University's Heritage College of Osteopathic Medicine, who led the study, said that the re-excavated Laetoli trackway is the earliest evidence of humans walking upright.
"There were at least two hominins walking in different ways on differently shaped feet at this time in our evolutionary history, showing that the acquisition of human-like walking was less linear than many imagine," said Jeremy DeSilva, a paleoanthropologist who co-authored the study with McNutt.
"In other words, throughout our history, there were different evolutionary experiments in how to be a biped," DeSilva said.
The Laetoli footprints had markedly different characteristics than the ones found in 1978, particularly their pattern of movement, known as cross-stepping.
"The trackway consists of five consecutive bipedal footprints," DeSilva said. "But the left foot is crossing over the right, and vice versa. We aren't sure what this means yet."
"Cross-stepping sometimes occurs in humans when we are walking on uneven ground," DeSilva explained. "Perhaps that explains this odd gait. Or perhaps just this individual hominin walked in a peculiar manner. Or maybe an unknown species of hominin was adapted to walk in this way," DeSilva added.
6.5 million-year-old footprints found on Crete
In 2002, researchers who had discovered hominid footprints on the Greek island of Crete discovered they were made an incredible 5.7 million years ago. Now, they say, they are pushing back the date even further, making it almost certain that they are much older.
Back in 2017, Dr. Per Ahlberg from Uppsala University and his colleagues determined that the footprints that had become fossilized in a rock on Crete were 5.7 million years old and made by a human ancestor.
This was a revolutionary finding, indicating it was possible that humans evolved in Europe —launching a curveball into African-origin evolutionary theory. But the newest research, just announced this week, shows that the fifty footprints are more than three hundred thousand years older than previously thought, according to a scientific paper published in Scientific Reports.
The hominid, who had earlier been thought to belong to the group of proto-humans called Graecopithecus freybergi, had been classified as such in 1944. Remains from this individual, affectionately named "El Graeco," were found outside Athens.
Study co-author Uwe Kirscher, an expert on paleogeography at the University of Tübingen, said in a statement "The tracks are almost 2.5 million years older than the tracks attributed to Australopithecus afarensis (Lucy) from Laetoli in Tanzania."
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