A 3D computerised model of the surface of the area near Lake Turkana in Kenya shows fossil footprints of Paranthropus boisei (vertical footprints) with separate footprints of Homo erectus forming a perpendicular path. Credit: Kevin Hatala/ Chatham University.

In a fossil first, scientists have found 1.5-million-year-old footprints of two different species of human ancestors at same spot.

The discovery by an international team of researchers, proves the theory that some ancient hominins were neighbours.

More than a million years ago, on a hot savannah teeming with wildlife near the shore of what would someday become Lake Turkana in Kenya, two completely different species of hominins may have passed each other as they scavenged for food.

Scientists know this because they have examined 1.5-million-year-old fossils they unearthed and have concluded they represent the first example of two sets of hominin footprints made about the same time on an ancient lake shore.

The discovery will provide more insight into human evolution and how species cooperated and competed with one another, the scientists said.

‘Hominin’ is a newer term that describes a subdivision of the larger category known as hominids.

Hominins includes all organisms, extinct and alive, considered to be within the human lineage that emerged after the split from the ancestors of the great apes.

This is believed to have occurred about six to seven million years ago.

The discovery,offers hard proof that different hominin species lived contemporaneously in time and space, overlapping as they evaded predators and weathered the challenges of safely securing food in the ancient African landscape.

Hominins belonging to the species Homo erectus and Paranthropus boisei, the two most common living human species of the Pleistocene Epoch, made the tracks, the researchers said.

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: “Their presence on the same surface, made closely together in time, places the two species at the lake margin, using the same habitat.”

A footprint hypothesised to have been created by a Homo erectus individual. Credit: Kevin Hatala/ Chatham University.

‘Within hours’

Feibel, who has conducted research since 1981 in that area of northern Kenya, a rich fossil site, applied his expertise in stratigraphy and dating to demonstrate the geological antiquity of the fossils at 1.5 million years ago. 

He also interpreted the depositional setting of the footprint surface, narrowing down the passage of the track makers to a few hours, and showing they were formed at the very spot of soft sediments where they were found.

If the hominins didn’t cross paths, they traversed the shore within hours of each other, Feibel said.

While skeletal fossils have long provided the primary evidence for studying human evolution, new data from fossil footprints are revealing fascinating details about the evolution of human anatomy and locomotion, and giving further clues about ancient human behaviours and environments, according to Kevin Hatala, the study’s first author, and an associate professor of biology at Chatham University in Pittsburgh.

Hatala, who has been investigating hominin footprints since 2012, said: “Fossil footprints are exciting because they provide vivid snapshots that bring our fossil relatives to life.

“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.

“That’s something that we can’t really get from bones or stone tools.”

A footprint hypothesised to have been created by a Paranthropus boisei individual. Credit: Kevin Hatala/ Chatham University.

3D analysis

Hatala, an expert in foot anatomy, found the species’ footprints reflected different patterns of anatomy and locomotion.

He and several co-authors distinguished one set of footprints from another using new methods they recently developed to enable them to conduct a 3D analysis.

Rebecca Ferrell, a programme director at the National Science Foundation who helped fund this portion of the research, said: “In biological anthropology, we’re always interested in finding new ways to extract behaviour from the fossil record, and this is a great example.

“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 co-operation and competition in shaping our evolutionary journey.”

Feibel described the discovery as “a bit of serendipity” and noted it has long been hypothesised that these fossil human species co-existed.

According to fossil records, Homo erectus, a direct ancestor of humans, persisted for one million years more, but Paranthropus boisei went extinct within the next few hundred thousand years. Scientists don’t know why.

Both species possessed upright postures, bipedalism and were highly agile, yet little is known about how these coexisting species interacted, both culturally and reproductively.

Trace fossils

The footprints are significant, Feibel said, because they fall into the category of ‘trace fossils’ – which can include footprints, nests and burrows.

Trace fossils are not part of an organism but offer evidence of behaviour. Body fossils, such as bones and teeth, are evidence of past life, but are easily moved by water or a predator.

Trace fossils cannot be moved, Feibel said.

He added: “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.

“The idea that they lived contemporaneously may not be a surprise. But this is the first time demonstrating it.

“I think that’s really huge.”

The research is published in Science.