On the left, a nearly 3.7-million-year-old fossil footprint is now thought to be man-made. To the right, the rear footprint of a young black bear.
Left: J. DeSilva / Right: E. McNutt
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Left: J. DeSilva / Right: E. McNutt
On the left, a nearly 3.7-million-year-old fossil footprint is now thought to be man-made. To the right, the rear footprint of a young black bear.
Left: J. DeSilva / Right: E. McNutt
The first humans to walk the earth nearly 3.7 million years ago did not have to walk alone. Fossil footprints in Tanzania show that two species of humans lived in the same place at the same time.
Scientists have long thought that an unusual set of tracks there were left by a bear walking on hind legs, but one analysis published in the journal Nature shows that is not the case. Instead, it seems that the tracks were left by some unknown early human species walking around the location at the same time as Australopithecus afarensis – species of the famous partial skeleton “Lucy. ”
Australopithecus afarensis has long been thought to be the only human species that lived that way back then, and scientists have considered it to be ancestor of modern man. But recent discoveries of other remains, such as the jaw, skull and metatarsal bones, have suggested that an unexpected diversity of hominins may have lived during this period.
These ancient footsteps were trapped by a volcano
At this particular prehistoric site, at Laetoli in northern Tanzania, all the footprints were made in the same mud. That means that individuals from these two early human species must have outgrown each other within hours or days, say. Ellison McNutt, a biological anthropologist at Ohio University Heritage College of Osteopathic Medicine.
It is possible that the unknown species that made the strange footprints may have “looked up at the landscape and seen a Australopithecus afarensis “It’s great that we can have two species of hominin living in the same place,” she said.
McNutt studies bipedalism because bipedal walking is a unique and distinctive human trait. “It’s a very strange way of moving around in the world and it’s very different from other animals,” she noted, adding that how and why humans evolved to do this remains to be seen. remains a mystery. “This seems to be one of the things that makes hominins and our lineage so different from other living primates.”
And vertical walking seems to make a comeback in human evolution. Millions of years ago, a volcano erupted and covered Laetoli in ash. That ash turned to mud, and all kinds of creatures left traces; When the volcano erupted again, another layer of ash preserved them. In the 1970s, paleontologists discovered traces of animals including ostriches, giraffes, hyenas, and of course, what was later identified as Australopithecus afarensis.
Human, or bear?
At the same time, workers discovered another set of rails that also appeared to show bipedal ability, but they didn’t look too human. In the end, the scientists decided that they must have been left behind by a young bear, since bears lived in Africa at the time. Bears’ hind paws can look like humans, bears can walk on two legs, and they don’t always leave distinctive claw marks.
“It makes sense,” said McNutt, who added that the more recognizable human footprints are so interesting that these other footprints have been ignored for decades.
However, she came across these forgotten footprints by chance while studying bear bipedalism while a graduate student at Dartmouth College. She realized that she and her colleagues could test the bear hypothesis with the help of a nearby black bear rehabilitation center in New Hampshire. It has young bears with paws about the same size as the footprints.
She explains: “We ended up with four little juvenile bears that we stood up and walked through the mud for apple sauce or maple syrup, which were so cute, as their reward. when it ends.
Walking on two legs may have happened more than once
By examining the footprints left by bears, and comparing them with mysterious fossil footprints as well as human and chimpanzee footprints, the team determined that the fossil’s features resembled humans. than. It looks like the right foot has a relatively large “big toe”.
Furthermore, the walking pattern preserved in the tracks shows a cross-stepping pattern, with the feet crossing in front of the midline of the body. Sometimes, people step sideways when walking over uneven surfaces or regaining their balance.
“It’s really another piece of proof that it’s not a bear, because bears don’t have the anatomical structure in their hips and knees to allow them to stand up and balance as they step over,” McNutt said. ”
The researchers also watched more than 50 hours of video footage of wild black bears and found that they almost never walked on their hind legs. “When a bear stands up, it usually clings to a tree,” says McNutt. “Or maybe he’ll take a step or two, but he usually doesn’t take four or more, which is what you really need to get to the five steps we’ve preserved at this site.”
All these evidences are convincing Stephanie Melillo, an anthropologist at the Max Planck Institute for Evolutionary Anthropology in Germany, who was not part of the research team. “They did a very convincing job demonstrating that the prints were not made by a bear,” she said, adding that the shape of the prints suggests that they were made by a bear. early humans are unknown.
“If it is the case that this is the second species, then this discovery shows Australopithecus afarensis and something else that was actually at the same time, at the same place,” said Melillo, who noted that this kind of association is difficult to make with such precision when fossilized bones are found in locations is different.
And that means that bipedalism need not have developed at once and progressed in a straight and progressive line the way modern humans walk today, but rather that different versions may exist. at the same time in different branches of the family tree.
The footprints, unlike bones, record actual early human behavior and allow scientists to imagine these distant but familiar species roaming the land at Laetoli.
“This site is unique,” Melillo said. “It’s not just two hominins. We see these hominins with birds, and with antelopes and hyenas, an entire faunal ecosystem of Africa. It really gives you a really good picture of the species. environment that the hominins occupy.”
