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Our first steps? Fossil may boost case for oldest ancestor

NEW YORK (AP) — Twenty years ago, scientists discovered a 7-million-year-old skull they concluded belonged to an upright-walking creature that was our oldest known ancestor. Not everyone was convinced. Now, investigators are back with more evidence that they say strengthens their case.

Their new study published Wednesday analyzed arm and leg fossils found near the skull in Africa, looking for signs of walking on two feet rather than four legs. When the first humans began to walk upright, it marked a key moment in our separation from the apes.

In the Nature journal article, the researchers again place the creature right on the human side of that evolutionary gap. The fossil species, named Sahelanthropus tchadensis, walked upright while still able to climb trees, they reported.

The species dates to about 7 million years ago, making it the oldest known human ancestor by far. That’s about a million years older than other known early hominins.

But it has been a source of fierce debate ever since the fossils were first unearthed in Chad in 2001.

The researchers, also led by scientists from the University of Poitiers in France, initially looked at the fossil creature’s skull, teeth and jaw. They argued that the creature must have walked on two feet and held its head up, 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 preliminary evidence.

The latest work includes a femur that was initially unrelated to S. tchadensis and was not studied for years. Other researchers from the French university found the bone in the laboratory collection and realized that it probably belonged to the fossil species.

Compared to bones from other species, the femur was a better fit for upright-walking humans than for knuckle-walking apes, according to the study.

“There is no feature. There’s just a whole pattern of features,” co-author Franck Guy said of his analysis at a news conference.

Still, the debate over the species is likely to 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 completely convinced,” Hammond said. “This could also be an ape fossil.”

Another French university researcher, Roberto Macchiarelli, had previously examined the femur and determined that the species was probably ape. 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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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.

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