The discovery of fossilized footprints reveals the moment two ancient human species crossed paths

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More than 1.5 million years ago, two different species of ancient humans crossed paths on a lakeshore, perhaps looking into each other’s eyes. These early precursors of Homo sapiens migrated across a landscape teeming with wildlife, including giant maribou storks that stood up to 2 meters (6.5 feet) tall.

A stunning discovery of fossilized footprints pressed into soft mud preserved the unexpected and extraordinary moment and suggests that the two distinct species of hominins were able to live as neighbors sharing a habitat, rather than competitors , who retained their own territory.

“It’s surprising that there are two species of similarly sized, large-bodied hominins in the same landscape,” said Kevin Hatala, lead author of a study on the footprints published Thursday in the journal Science.

“We see them in the same lakeshore environment, passing within that area within hours to a few days. They probably would have been aware of each other’s existence. They saw each other and may have interacted with each other,” added Hatala, who is an associate professor of biology at Chatham University in Pittsburgh.

The first part of the find occurred in July 2021 during an excavation at Koobi Fora on the eastern shore of Lake Turkana in Kenya, where the skeletal remains of several early human relatives were found. A hominin footprint as well as several other tracks of large birds were discovered during this excavation. The team decided to rebury the tracks with fine sand until a detailed excavation was possible.

The excavation took place in 2022, when Hatala and his colleagues uncovered 23 square meters (248 square feet) of sediment and uncovered eleven additional hominin tracks similar to the first in a lineage that suggested they came from the same person, as well as three isolated footprints which were aligned in a vertical direction.

The researchers also found 94 non-human tracks from birds and cow- and horse-like animals. The largest bird track was 27 centimeters (10.6 inches) in diameter and probably belonged to a species of giant stork called Leptoptilos.

“There is a long track with 12 (hominin) footprints in it. It was done at a decent walking pace…especially since they were walking through mud. In the end there is no clear goal,” said Hatala.

“It’s hard to say what exactly they were doing, but they were walking in this perfect mud zone,” he said. “If you think about the shoreline of a lake or a modern beach, you have kind of a narrow area where the mud is perfect for footprints. If you move too far in this direction it will be too dry, if you move too far in the other direction it will be too wet. And they almost walk in a straight line through the perfect area for their footprints, which is very lucky for us,” he said.

The three other footprints perpendicular to the track were scattered across the site. Hatala believes they come from three different individuals and that their other tracks may have been covered up by other animals walking on the surface at the same time.

Preserved untouched

Hatala and his colleagues were unable to date the footprints directly. But Hatala said the fossils were found under a layer of volcanic ash in the same site called the Elomaling’a Tuff – and were therefore “slightly older” than this – which the study said was dated to 1.52 million years ago.

However, the researchers said they were confident that the tracks were imprinted within hours to a few days of each other because there were no cracks on the surface of the footprints, which would be the case if they were exposed to air and dried in the sun a longer period of time.

Instead, the scientists said the prints were all similarly preserved pristinely beneath the accumulating layers of sediment, thanks to the fine and muddy sand that gently covered the tracks shortly after they were formed.

“This was probably a delta system with a lot of shallow, low-energy water in that area and a lot of nice muds,” Hatala said.

The term hominin refers to all species in the human family tree that emerged after splitting from the ancestors of great apes 6 to 7 million years ago. This group includes recently extinct species such as the Neanderthal, which disappeared 40,000 years ago, and the Australopithecus afarensis, represented by the famous Lucy skeleton in Ethiopia, which was 3.2 million years old.

Homo sapiens, our own species, is the only living species of hominin, making the idea of ​​encountering another species from the same lineage particularly enticing. The researchers found some clues about which groups of ancient people intersected in this encounter.

Who did the footprints belong to?

The team concluded that hominins of the species Homo erectus and the small-brained Paranthropus boisei left the footprints. P. bosei made the long footprint, while Homo erectus made the other three footprints, the study found. Skeletal remains of both species were found at the site.

However, it was not immediately clear that the footprints came from two different species. Hatala, an expert in foot anatomy, only realized after detailed 3D imaging and analysis that they reflected different gait, posture and movement patterns.

Through field and laboratory experiments, he compared the footprints with those of living humans, including 59 of the Daasanach people of Ethiopia, who do not normally wear shoes, as well as other fossilized hominin prints and chimpanzee tracks.

Hatala found that the trail of 12 footprints was left by an individual whose footprints did not fall within the range of variation of Homo sapiens, in contrast to the three scattered footprints that were more similar to those of living humans.

“Homo erectus looks very similar to modern humans from the neck down and is the best candidate to be a direct ancestor of ours during this time period.” “We assume that these more human-like footprints are more likely Homo erectus “Just because the rest of their anatomy is so human,” Hatala said.

“Paranthropus boisei, they look completely different. Most of the fossils that are confidently attributed to them are skulls or teeth. They have very large jaws, very large teeth and large attachments for the chewing muscles. It looks like they adapted to a very different diet than Homo erectus,” he said. Hatala explained that Bosei probably had a plant-based diet, while Homo erectus was more of an omnivore.

Hatala and his colleagues reviewed ancient fossil data from the site and found evidence that the two species overlapped at the site over a significant period of time – perhaps 100,000 years, he said.

“That’s exciting to see and for us it implies that the direct competition between the two must have been relatively low and that they must have been comfortable with living in the same environment. They didn’t drive each other away,” he said.

“It would have been a risk area where hippos, crocodiles and other dangerous animals would also have lived,” Hatala added. “So there must have been an attraction for both of them to visit these areas again and again over such a long period of time.”

According to the study, the footprints are the first physical evidence that different hominin species overlapped in exactly the same time and space to avoid predators and find food in the ancient landscape. Homo erectus continued to thrive for a million years. However, Paranthropus boisei became extinct within the next hundred thousand years. Scientists don’t know why.

Briana Pobiner, a researcher and museum educator at the Smithsonian National Museum of Natural History’s Human Origins Program, said it was “mind-blowing” to find footprints of not just one, but two species that roamed the same area.

“Perhaps they were actively competing for the same food; Maybe they were just eyeing each other suspiciously from across a meadow. Maybe they completely ignored each other,” said Pobiner, who was not involved in the new research.

While it is the first time that footprints indicate that hominins of two species met directly, genetic evidence has shown that Neanderthals interbred with Homo sapiens and Denisovans, a poorly understood hominin known from only a few fossils . Denisova Cave in Siberia was home to a girl who had a Neanderthal mother and a Denisovan father.

Perhaps, says Pobiner, P. boisei and H. erectus “were so similar that they even occasionally mated with each other.”

“This finding shows us that they lived in the same place at the same time and were practically walking next to each other,” she said.

“It’s impossible to go back in time to actually observe these species 1.5 million years ago – but to have both of their footprints on the same surface? This is the next best thing.”

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