A newly discovered set of footprints in Kenya provides the first evidence that two different species of ancient human relatives walked on the same ground at the same time 1.5 million years ago.

Researchers involved in the discovery say the footprints belong to the species Homo erectus and Paranthropus boisei, and were left within hours to days of each other, meaning that when the two crossed paths, reveals new mysteries about what happened.

According to research on this discovery, Published in Science on Thursdaythe footprints were buried in dry mud near a lake in northern Kenya, and were buried in deposits of prominent fossil sites. By analyzing the print shapes and strike patterns, the researchers found that the two sets were different. They concluded that the best explanation was that two different species left the footprints.

This research advances anthropologists and paleontologists’ understanding that ancient human relatives likely interacted and coexisted. This also raises the question of what kind of relationship these species had.

“We think these individuals, the two species that were there, were probably aware that there were members of another species nearby. They saw each other and thought each other was a member of another species. “This raises the question of what that interaction was,” said Kevin Hatala, an associate professor of biology at Chatham University and lead author of the study. “Were they competitors? Were they totally okay with each other there?”

Previously discovered fossil skeletons of Homo erectus and Paranthropus boisei indicated that both species lived in the area at some point, but the new discovery provides evidence of a direct duplication.

It also shows that the two species walked on two legs in very different ways.

Although both Homo erectus and Paranthropus boisei are related to humans, they have very different characteristics and their fates in the human evolutionary tree took very different paths.

Homo erectus had an anatomy similar to humans from the neck down. This species may have used stone tools and cooked over fire. Its members probably had a varied diet that included meat.
The species eventually spread to Asia, Indonesia, and other regions, and survived for more than a million years after the newly discovered footprints were made.It last appeared in the fossil record just over 100,000 years ago..

“Many have considered themselves to be as good candidates as our direct ancestors,” Hatala said. “They seem to be a very successful species.”

Paranthropus boisei, on the other hand, featured a smaller brain, huge masticatory muscles, and large molar teeth. William Harcourt Smith, an associate professor of anthropology at Lehman College who was not involved in the study, said the species eats difficult-to-eat foods like hard nuts or grinds hard, poor-quality foods like shrubs. It is highly likely that they evolved in this way.

This species did not persist on Earth as long as Homo erectus.

“They probably went extinct not very long after that, within the next few hundred thousand years,” Hatala said, referring to the time of the footprints. He added that no one knows exactly what happened, but it’s possible that environmental changes may have restricted the animal’s specialized diet.

The footprints were first discovered in 2021 at a site called Koobi Fora while researchers were excavating other fossils. This location has become a fossil hotspot. The uplifted rocks expose older sedimentary layers on the surface, giving researchers access to the bones of ancient humans and other animals.

The following year, researchers unearthed about a dozen footprints that appeared to be walking in a line, and later discovered other footprints running at right angles.

“We think these footprints were created in the mud of this lakeshore environment. Something happened that brought sediment on top of it. It could have been deposited by a small flood or by rising water levels. “It’s possible that something was brought in and the footprints were formed and quickly buried,” Hatala said.

The muddy footprints were not trampled by other animals and showed no signs of cracking before being buried in the sand. Researchers said that means they were separated from each other within hours or days.

“The sediment protected them, prevented them from cracking, and allowed them to remain in the geological record,” Hatala said.

He and his co-authors believe that the two species may have been able to coexist in this region because their diets were very different. It is possible that they competed for resources and were in a hostile relationship. This species appears to have lived in the same area for hundreds of thousands of years.

Harcourt Smith, a research paleontologist at the American Museum of Natural History, said the researchers’ analysis was sound and the site was unique.

“I want to emphasize how unusual it is that a site like this exists, how special it is, and the great opportunity we have to find out more,” he said.

Broadly speaking, over the past seven million years of evolution, it has become increasingly clear that different ancient human species interacted in different habitats, Harcourt-Smith added. The evolutionary path to modern humans is full of side branches and species, such as Paranthropus boisei, which represent evolutionary dead ends.

“Human evolution is complex and messy, and there are many experiments being done. It’s not a straight line,” he said.

Over the past few decades, scientists have developed genetic and archaeological evidence showing that: Humans, Denisovans, and Neanderthals overlapped and sometimes interbred. Although the new study does not mention interbreeding, it does provide a clearer picture that even older species overlapped and had more interactions than previously understood.

The researchers completed their work at the Koobi Fora site, photographing and recording the footprints in a variety of ways before concealing them for future generations, said Craig, another author of the research paper.・Mr. Feibel said.

“The footprints need to be carefully refilled with non-damaging sediment to prevent erosion,” he says.