NEW YORK (AP) – Twenty years ago, scientists discovered a 7-million-year-old skull that they concluded belonged to an upright-walking creature that was our oldest known ancestor. Not everyone was convinced. Now the researchers are back with more evidence that they say bolsters their case.
Their new study published on Wednesday analyzed fossils of arms and legs found near the skull in Africa, looking for signs of walking on two feet instead of four. When the first humans began to walk upright, it marked a key moment in our separation from the apes.
In the paper published in the journal Nature, the researchers again place the creature only on the human side of this evolutionary divide. The fossil species, called Sahelanthropus tchadensis, walked upright while still being able to climb trees, they reported.
The species has been dated to around 7 million years ago, making it the oldest known human ancestor by far. That’s about a million years older than other known hominids.
But it has been a source of fierce debate since the fossils were first unearthed in Chad in 2001.
The researchers – also led by scientists from the University of Poitiers in France – initially analyzed the skull, teeth and jaw of the fossil creature. They argued that the creature must have walked on two feet and held its head upright, based on the location of the hole in the skull where the spinal cord connects to the brain.
Other experts were not swayed by the early evidence.
The most recent work includes a femur that was not linked to S. tchadensis at first and has not been studied for years. Other researchers at the French university found the bone in the laboratory’s collection and realized that it likely belonged to the fossil species.
Compared to the bones of other species, the femur matches up better with humans who walk upright than with monkeys who walk with their knuckles, according to the study.
“There is no feature. There’s just one total pattern of features,” co-author Franck Guy said of his analysis at a press conference.
Still, the debate over the species will likely continue.
Ashley Hammond, a scientist at the American Museum of Natural History in New York, said more research is needed to find the creature’s place on the evolutionary tree.
“I’m still not entirely convinced,” Hammond said. “This could also be a fossil ape.”
Another researcher at the French university, Roberto Macchiarelli, had previously examined the femur and determined that the species was likely a monkey. Looking at the new study, Macchiarelli said he still doesn’t believe the species was a hominid, although it may have walked on two legs at times.
Rick Potts, director of the Smithsonian’s Human Origins Program, said the femur puts the species “in a better position” as a possible early human ancestor. But the real confirmation comes down to a common saying in the field: “Show me more fossils.”
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