Our first steps? The fossil may strengthen the case for its first ancestor

NEW YORK (AP) — Twenty years ago, scientists discovered a 7-million-year-old skull that they concluded belonged to a creature that walked upright and was our earliest known ancestor. Not everyone was convinced. Now, the researchers are back with more evidence they say bolsters their case.

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

In the article in the journal Nature, the researchers again place the creature squarely on the human side of this evolutionary divide. The fossil species, called Sahelanthropus tchadensis, walked upright while still being able to climb trees, they said.

The species has been dated to around 7 million years ago, making it the oldest known human ancestor, by a long shot. This is about a million years older than other early known hominids.

But it has been a source of heated debate since the fossils were first discovered in Chad in 2001.

The researchers – also led by scientists at the University of Poitiers in France – first examined the fossil creature’s skull, teeth and jaw. They argued that the creature must have walked on two legs 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 latter work includes a femur that was not initially associated with S. tchadensis and remained neglected for years. Other researchers at the French university found the bone in the lab’s collection and realized it probably belonged to the fossilized species.

Compared to bones from other species, the femur was a better match for humans who walked upright than apes who walked on joints, the study found.

“There isn’t one feature. There’s just an overall pattern of features,” co-author Franck Guy said of their analysis in a press briefing.

However, the genre debate 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 not fully convinced yet,” Hammond said. “That might as well be a fossilized ape.”

Another researcher at the French university, Roberto Macchiarelli, had previously examined the femur and determined that the species was likely an ape. Reviewing the new study, Macchiarelli said he still doesn’t think the species was 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 “on a better footing” 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 Section is supported by the Howard Hughes Medical Institute Science Education Division. AP is solely responsible for all content.

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