One of the unknown ancestors of man walked on his hind legs like a bear

A new study shows that the mysterious footprints discovered in Tanzania show an abnormal cross-walking pattern in which one foot crosses the other while walking.

The earliest evidence of upright walking among anthropomorphs (a group that includes humans, our ancestors, and our closest evolutionary relatives) is the footprints discovered in 1978 in Laotoli, northern Tanzania. The footprints date back to about 66.3 million years ago, and previous research has shown that they were copied from the south (Australopithecus afarensis) Have been created.

Southern is a species that is considered to be one of the main candidates for the direct ancestor of human descent, and the famous 2.3 million-year-old Lucy belongs to the same species. Other footprints discovered in nearby Area A in 1976 were more obscure.

One possibility was that these unusual footprints (five in a row) were left by an unknown human being. Another possibility was that the footprints were created by a bear walking on its hind legs. Laetoli A’s strange footprints were never fully explored. Recently, scientists have thoroughly studied these footprints and compared them to human, bear and chimpanzee footprints to solve the mystery.

“Ellison McNaughton, lead author and bioanthropologist at Ohio State University, says:

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One of the first major obstacles at the beginning of this research was to be able to find the main Laetoli A footprints of the initial discovery. We feared that exposure to the sun and decades of seasonal rain would destroy the early fossilized footprints. Fortunately, when the researchers returned to Laotoli to re-explore, they found that the rain had washed away the sediments near the original footprints, but the footprints had been preserved.

Scientists cleaned, measured, photographed and scanned the footprints three-dimensionally. “Looking at the fully explored footprints of A, we immediately realized that they were really interesting and different from the other two-footed footprints found in Laotoli,” Maknat said.

Maknat and his colleagues then collaborated with the Black Bear Rescue and Rehabilitation Center in Lyme, New Hampshire. They found four semi-wild juvenile black bears in the center whose feet were about the size of those seen in Laetoli A footprints. The researchers used maple syrup or apple puree to tempt bears to stand and walk on their hind legs on a muddy path to keep track of their feet.

The researchers found that Laetoli A’s footprints were more like human footprints than bears. Jeremy Disilova, lead author of the study, said:

As the bears walk, they take wide steps and stumble back and forth. They can not walk like what is seen in the footprints of Area A because their pelvic floor muscles and knee shape do not allow them to move and balance.

Footprints found in Laotoli / footprints

Laotian A3 footprint (left) and Laotian G1 footprint (right)

In addition, the legs that left the observed traces were more like the feet of a raven than a bear. Bears’ toes and feet are like a fan, and they have narrow toe heels, while Laetoli A footprints, like human footprints, are square with large, distinctive toes and wide heels.

The researchers also collected more than 50 hours of video of wild black bears. The bears walked on their hind legs for less than one percent of the total time observed, so it is unlikely that the bear’s footprint found in Laotoli A; Especially considering that no traces were found there to indicate that the creature walked on all fours. In addition, the scientists noted that although thousands of animal fossils were found in Laotoli, none were related to bears.

Of course, the Laetoli A footprints are not like the footprints of any known anthropomorphs. These footprints are unusually wide and short, and the feet that created them may have had a big toe that resembles the thumb of copies capable of grasping objects.

  Topographic map of ancient Tanzania / topographic map of footprint

Topographic map of the footprints found in Laitoli Area A in Tanzania

Overall, Maknat et al.A. afarensis) has been created. Maknat says:

Laotian A traces are one of the oldest clear evidence in the fossil record of anthropogenesis, showing that several anthropogenic species were present in the same area at the same time. It is inconceivable that the person who created footprint A could look across the landscape and people A. afarensis To see.

The strange thing is that this humble man had an unusual and cross-walking style, in which each foot crossed the midline of the body to be in front of the other foot. Makunat explains:

This person’s ability to walk cross-legged is another piece of evidence that the Laetoli A footprint was created by a human being. Primates, such as chimpanzees, which walk mainly on their four limbs, lack the necessary anatomical adaptations in the thighs and knees to allow them to maintain balance when they cross the midline of the body and stand in front of the other leg. Although humans do not usually cross paths, they sometimes do. This walking method can be used as a strategy to help walk on uneven or slippery surfaces.

However, cross-walking may not have been due to the human-to-balance effort. According to Maknat:

A possible option is for this unique human being to walk in an unusual way. It is also possible that this unknown species was adapted to walk this way. By discovering more clues we can answer these questions more clearly.

Researchers plan to continue exploring Laetoli A. “Other footprints of this person or other people of the same kind may give us more insight into how they walked the earth and how they belonged,” Maknat said.

The findings are published in the journal Nature.

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