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These mysterious footprints are not of a bear, but of an unknown human ancestor.

Footprints discovered in 1978 in Tanzania and dated to 3.66 million years ago have been widely regarded as the oldest undisputed evidence of upright walking in the human family tree.

Discoveries at a site known as the Laetoli G site are commonly accepted as belonging to Australopithecus afarensis – the species of the famous “Lucy” skeleton, possibly the best known fossil in the world.

However, the footprints of the Laetoli G site weren’t the only ancient tracks that researchers found at that time. A set of footprints a mile away at a site called Site A of Laetoli was attributed to a young bear walking upright on its hind legs because they were very different from the tracks left by Australopithecus afarensis.

Now, researchers believe the Laetoli site A footprints may belong to a different human ancestor, who also walked on both legs, a revelation that could rewrite this chapter of human history.

“These footprints demonstrate that the evolution of upright walking was more complicated and more interesting than we previously thought,” said Jeremy DeSilva, associate professor in the department of anthropology at Dartmouth College and co-author of the research published in the journal Nature, on Wednesday .

“At this time in our evolutionary history, there were at least two hominids, walking in different ways, with different shaped feet, showing that the acquisition of walking as a human was less linear than many imagine.”

The human version of walking on two legs, known as bipedalism, is unique among mammals, and conventional thinking was that it had a unique evolutionary origin.

old sediments

Laetoli is a beautiful arid grassland environment northwest of Ngorongoro Crater in northern Tanzania, with acacia trees scattered across a landscape inhabited by zebras and giraffes. Seasonal rains cut through ancient sediments, exposing a layer of hardened volcanic ash 3.66 million years old, which DeSilva said preserves the footprints of thousands of ancient antelopes, elephants, large cats, birds and insects – and our hominid ancestors .

Site A was never fully excavated and was covered shortly after the footprints were discovered by pioneering paleontologist Mary Leakey in 1977 or 1978, said DeSilva. It is unclear whether the cover was deliberately done to protect the footprints or whether the rains washed away sediment from the adjacent slope above them.

Unlike the famous G-site footprints, these marks were unusually shaped and suggested an upright walking movement that had a peculiar cross-step shape, in which each foot moved over the midline of the body to touch in front of the other foot. , said Stephanie Melillo, a paleoanthropologist and postdoctoral researcher in the department of human evolution at the Max Plank Institute for Evolutionary Anthropology in Leipzig, Germany. She was not involved in the research.

One explanation given at the time for the enigmatic footprints was that they had been made by a bear walking on two feet, although Leakey wondered if they were left by a hominid with an irregular gait.

“Scientists were not convinced by any of the explanations. In the end, the marks left at site A were more easily forgotten than explained,” Melillo said in a commentary on the research published in Nature.

DeSilva said he decided to re-dig the site after he and his colleagues collected footprint data from humans, chimpanzees and bears and that cast doubt on the bear hypothesis. However, it was a challenge to re-examine the five consecutive footprints.

“Mary Leakey made exquisitely detailed maps of footprint locations. With her map, we were able to estimate where the marks should be. We started digging, hoping for the best, but fearing that forty years of seasonal rains had washed them away,” DeSilva said via email.

“The soil was hard as cement and it took a hammer and chisel to reach the footprint layer, which we needed to gently dig out with a stiff bristle brush and tongue depressor. Fortunately, the footprints have been beautifully preserved.”

After cataloging the original marks, they compared them to the footprints of black bears (Ursus americanus), chimpanzees (Pan troglodytes) and modern humans (Homo sapiens).

They also obtained over 50 hours of wild black bear video. The bears walked on two feet less than 1% of the time. That makes it unlikely that a bear left footprints on Laetoli, especially since no footprints were found of that individual walking on all fours, the researchers said.

on the scale

DeSilva said that when non-human animals walk on two legs, they cannot balance on one leg. This means that they sway back and forth as they walk, producing spaced footprints.

But early in human evolution, changes in the position of our ancestors’ hip and knee muscles allowed upright hominids to balance on one leg and walk in a straight line with no sideways movement.

Melillo agrees that the new excavation revealed “a combination of diagnostic features of hominids.”

“The big toe and the second finger are similar in length; the impression made on the floor by the thumb is much larger than that recorded by the second finger; impressions made by the fingers and the rest of the foot are continuous; and the heel is wide,” she said.

“Still, site A footprints are unlike any other hominid. The footprints are unusually long and short, and the feet responsible for their creations may have had a toe capable of gripping, similar to the toe of gorillas.”

DeSilva said we would need to find fossils to learn more about what this hominid looks like. But he said the foot size suggests the individual would be three feet tall.

(Translated text. Read the original here).

Reference: CNN Brasil

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