Fossil footprints place two early human species in the same area at the same time

(CN) — More than a million years ago, two ancient human species may have crossed paths on a lake shore, leaving behind footprints that provide evidence for long-hypothesized ideas about human evolution and early species interaction.

Scientists have evidence that two early human species may have crossed paths while searching for food in the area we now call Lake Turkana in Kenya over one million years ago, according to a new study published Thursday in the journal Science.

While studying 1.5-million-year-old fossils unearthed from the region, a team of scientists discovered ancient footprints left by both species at around the same time on an ancient lake shore.

“Fossil footprints are exciting because they provide vivid snapshots that bring our fossil relatives to life,” Kevin Hatala, the study’s first author and an associate professor of biology at Chatham University, said in a statement.

The discovery offers new insight into human evolution, particularly between the two early human species, known as hominins — a term for a subdivision of hominids. Hominins are all organisms within the human lineage once they split from the ancestors of the great apes, around six to seven million years ago.

The footprints were identified as hominins belonging to two species: Homo erectus and Paranthropus boisei. The species are two of the most common living human species of the geological period known as the Ice Age or the Pleistocene Epoch.

“Their presence on the same surface, made closely together in time, places the two species at the lake margin, using the same habitat,” Craig Feibel, an author of the study and a professor in the Department of Earth and Planetary Sciences and Department of Anthropology in the Rutgers School of Arts and Sciences, said in a statement.

Feibel has conducted research in the area since 1981 and used stratigraphy and dating to pinpoint the estimated age of the trace fossils. Stratigraphy is a branch of geology that uses the position and order of rock layers to narrow down timeframes. He also determined that the tracks were left within mere hours of each other.

“This proves beyond any question that not only one, but two different hominins were walking on the same surface, literally within hours of each other,” Feibel said.

Typically, skeletal fossils offer primary evidence of human evolution, but fossil footprints help fill in gaps about the evolution of human anatomy and movement.

“With these kinds of data, we can see how living individuals, millions of years ago, were moving around their environments and potentially interacting with each other, or even with other animals,” Hatala said. “That’s something that we can’t really get from bones or stone tools.”

Hatala has been investigating hominin footprints since 2012 and is an expert in foot anatomy. He and the other scientists used recently developed methods to conduct a 3D analysis of the prints and analyze differences between the footprints.

“In biological anthropology, we’re always interested in finding new ways to extract behavior from the fossil record, and this is a great example,” Rebecca Ferrell, a program director at the National Science Foundation, said in a statement.

“The team used cutting-edge 3D imaging technologies to create an entirely new way to look at footprints, which helps us understand human evolution and the roles of cooperation and competition in shaping our evolutionary journey,” Ferrell said.

The scientists discovered the fossil footprints in 2021 with the help of a field team of local residents in Kenya who have been highly trained to scour the area after heavy rains. The team started to excavate the area after noticing fossils on the surface and finding giant bird tracks before spotting the first hominin footprint.

After that, another team was assembled to excavate the footprint surface in 2022.

The discovery is significant because it offers evidence for the long-hypothesized notion that the early human species coexisted.

“The idea that they lived contemporaneously may not be a surprise. But this is the first time demonstrating it,” Feibel said. “I think that’s really huge.”