Important steps on the Arabian Peninsula

Around 120,000 years ago, someone trudged across the Arabian Peninsula, with horses, camels and even elephants. We don’t know who it was, but their footprints remain at the gateway between Africa and Eurasia, according to researchers who have spent time exploring and investigating the fossilised imprints.

In a paper in the journal Science Advances, an international team led by Mathew Stewart from Germany’s Max Planck Institute for the Science of Human History describe fossilised footprints found in an ancient lake deposit in Saudi Arabia’s Nefud Desert.

They say they are the earliest dated evidence for human movements into that part of the world, contemporary with well-known human dispersals from Africa to the Levant. And it may be an indicator of the route humans took from Africa to Asia.

While the earliest fossils of Homo sapiens found outside of Africa date back to about 210,000 years ago in southern Greece and 180,000 years ago in the Levant region of Western Asia, the routes that humans used to spread beyond Africa have largely remained unknown.

Squeezed between Africa and Asia, the Arabian Peninsula seems like a logical place to look, but remained understudied, say the researchers.

While humans repeatedly dispersed into the peninsula’s interior at times when its harsh deserts were transformed into lush grasslands, when, who, what they took with them and what they found when they got there, has remained elusive.

The researchers found a total of 376 tracks, including seven hominin, 44 elephant and 107 camel footprints, in an exposed section of sediment which they estimated to be between about 112,000 and 121,000 years old. They worked out the age of the imprints by dating sediments found directly below and above the footprints.

“We immediately realised the potential of these findings,” says Stewart. “Footprints are a unique form of fossil evidence in that they provide snapshots in time, typically representing a few hours or days, a resolution we tend not get from other records.”

From the size and orientation of the human footprints, there were likely two or three individuals travelling together.

Previous research by other groups has found that, during this time period, Homo sapiens were spreading through the Levant, but there is no evidence Homo neanderthalensis were in the area.

Comparing the hominin tracks with modern humans and neanderthal also suggests those that left the footprints were taller, had longer feet, and smaller mass. Together, Stewart and colleagues say that these tracks must have belonged to Homo sapiens.

That particular point in time is of interest to researchers. Falling in an interglacial period, the conditions of the time were far different to what we see now. Humidity across the region would have been much higher, say the researchers, with the deserts becoming grasslands with permanent lakes and rivers.

This climate upheaval provided an opportunity for Homo sapiens to move across the area which would have otherwise been a desert barrier, say the researchers.

The fact there is such a high density and diversity of footprints in the sediment also suggests that animals may have been congregating around the lake in response to dry conditions and diminishing water supplies, say the researchers.

Humans would also have been visiting the lake for water, and possibly foraging the local area for food. Probably hunting as well. But it’s most likely they were only passing through, and not settling permanently.

“We know people visited the lake, but the lack of stone tools or evidence of the use of animal carcasses suggests that their visit to the lake was only brief,” says Stewart.

“The presence of large animals such as elephants and hippos, together with open grasslands and large water resources, may have made northern Arabia a particularly attractive place to humans moving between Africa and Eurasia,” says Michael Petraglia, also from the Max Planck Institute, who oversaw the research.