Have fossil footprints been left by extinct bear species or human ancestors?

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Through Christina Larson, Associated Press

Updated: 2 hours ago Posted: 2 hours ago

WASHINGTON – The prehistoric footprints that have puzzled scientists since the 1970s are getting a second look: were they left by extinct animals or by human ancestors?

When famous paleontologist Mary Leakey first discovered the footprints in Tanzania 40 years ago, the evidence was ambiguous.

Instead, Leakey focused his attention on other fossil footprints that could be more clearly linked to early humans. These footprints, found at a site called Laetoli G, are the first clear evidence of the first humans walking upright.

Decades later, a new team re-searched the puzzling footprints, found at a site called Laetoli A, and made photos and 3D scans available to other researchers to continue the debate.

The research was published Wednesday in the journal Nature.

“These prints have been in the mystery category for 40 years,” said Rick Potts, who heads the Smithsonian Institution’s Human Origins Project.

“It’s a really exciting idea to rehumidify them and study them again,” added Potts, who was not involved in the research.

What has long puzzled scientists is that these traces – large footprints with enlarged fifth toes and estimated to be around 3.7 million years old – do not closely match anything scientists have identified elsewhere. .

“They did not have the proper weight and foot movement to be easily identified as humans, so other explanations were sought,” including the fact that they could be from an extinct species of bear, said Dartmouth co-author and paleoanthropologist Jeremy DeSilva.

He and other researchers returned to the site in 2019 and used Leakey’s original maps to locate the enigmatic footprints, preserved in a layer of volcanic ash that had cooled and hardened.

Ohio University co-author Ellison McNutt studied the foot mechanics of black bear cubs at a New Hampshire wildlife rescue center to see if a small bear walking on its hind legs could leave similar footprints .

She was holding a tray of applesauce to entice the cubs to walk towards her. Each step was recorded in a trail of mud, to be analyzed.

Bears walking upright first put weight on the heels of their feet, like humans, she said. “But the proportions of the feet are not the same.” She concluded that the fossil footprints were not left by bears.

Other factors, such as the spacing of the footprints, led the study authors to conclude that the footprints were left by a previously unknown species of a very ancient human ancestor.

Not everyone is convinced.

Smithsonian’s Potts said it was a mix between an ancient bear or an ancient human, adding that an ancient bear may have walked differently from a modern black bear.

William Harcourt-Smith, a paleoanthropologist at the American Museum of Natural History who was not involved in the research, said he was convinced it was not a bear, but was not sure whether it is a primitive human being.

“These footprints could still be from some form of a non-human ape,” he said.

If two different species were walking upright in the landscape at the same time, it suggests different simultaneous experiences of bipedalism, complicating the conventional view of human evolution as strictly linear.

“It’s really cool to think about it,” said Harcourt-Smith.

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