An international team of archaeologists and paleoanthropologists has found ancient human and animal footprints on the surface of an ancient lakebed in the Nefud Desert, Saudi Arabia. The footprints, dated to roughly 120,000 years ago, are contemporaneous with an early Homo sapiens out-of-Africa migration and represent the earliest evidence of our species in the Arabian Peninsula.
“At certain times in the past, the deserts that dominate the interior of the Arabian Peninsula transformed into expansive grasslands with permanent freshwater lakes and rivers,” said co-lead author Richard Clark-Wilson, a Ph.D. student at Royal Holloway at the University of London.
“It was during these periods of climatic upturn that human and animal populations dispersed into the interior, as shown by the archaeological and fossil record.”
The researchers recorded a total of 376 fossilized footprints at the Alathar freshwater paleolake site in the western Nefud Desert.
“We immediately realized the potential of these findings,” said first author Dr. Mathew Stewart, a scientist in the Max Planck Institutes for Chemical Ecology, the Science of Human History, and Biogeochemistry.
“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.”
“Seven hominin footprints were confidently identified, and given the fossil and archeological evidence for the spread of Homo sapiens into the Levant and Arabia between 130,000 and 80,000 years ago and absence of Homo neanderthalensis from the Levant at that time, we argue that Homo sapiens was responsible for the tracks at Alathar,” the scientists said.
“In addition, the size of the Alathar footprints is more consistent with those of early Homo sapiens than Homo neanderthalensis.”
“Four of the human prints were found adjacent to one another along the south-western edge of the ancient lake,” the researchers said.
“Given their similar orientation, distances from one another, and differences in size, they are interpreted as two, or up to three, individuals traveling in concert.”
“It appears that the Alathar lake was only briefly visited by humans,” they said.
“It may have served as a stopping point and place to drink and forage during long-distance travel, perhaps initiated by the arrival of dry conditions and dwindling water resources.”
The authors identified elephant, horse, camel and bovid footprints at the Alathar site.
They also recovered 233 fossils, including the remains of oryx antelopes and elephants.
The dense concentration of footprints and fossils as well as evidence from the lake sediments suggest that the animals may have been congregating around the lake in response to dry conditions and diminishing water supplies.
“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,” said co-lead author Dr. Michael Petraglia, a researcher at the Max Planck Institute for the Science of Human History, the National Museum of Natural History and the University of Queensland.
To find the age of the fossil footprints, the team dated sand grains buried within the ancient lake deposits.
“Sand grains act as natural clocks as they record the time elapsed since they were last exposed to sunlight,” said co-author Professor Simon Armitage, a researcher in Royal Holloway at the University of London and the University of Bergen.
“Once the sands are buried in the lake sediments, they are protected from sunlight and the natural clock begins ticking.”
“We believe that the ancient lake and associated footprints to be about 120,000 years old.”
“The age of the footprints is of interest as they date to a period known as the last interglacial, a time of relatively humid conditions across the region and an important moment in human prehistory,” added co-author Professor Ian Candy, also from Royal Holloway at the University of London.
“Environmental changes during the last interglacial would have allowed humans and animals to disperse across otherwise desert regions, which normally act as major barriers during the less humid periods, such as today.”
“These findings suggest human movements beyond Africa during the last interglacial extended into Northern Arabia, highlighting the importance of this region for the study of human prehistory.”
The findings were published in the journal Science Advances.
Mathew Stewart et al. 2020. Human footprints provide snapshot of last interglacial ecology in the Arabian interior. Science Advances 6 (38): eaba8940; doi: 10.1126/sciadv.aba8940