A fossilised finger bone of an early modern human was discovered in the Nefud desert of Saudi Arabia, dating to approximately 85,000 years ago. The uncovered finger bone is the oldest directly dated Homo sapiens fossil outside of Africa and the Levant and indicates that early dispersals into Eurasia were more expansive than previously known.
Before this discovery, it was believed that early dispersals into Eurasia were unsuccessful and remained restricted to the Mediterranean forests of the Levant, on the doorstep of Africa. According to a new study, the finding from the Al Wusta site shows that there were multiple dispersals out of Africa, and these spread farther than previously thought.
Findings of the study were published in the journal Nature Ecology and Evolution this week. The study is part of a project led by the Max Planck Institute for the Science of Human History, aiming at conducting archaeological fieldwork in the Nefud desert of Saudi Arabia.
At the time the finger was buried, the climate of the Arabian Peninsula was humid and monsoonal. The desert was a lush grassland that humans were able to colonise.
This early incursion into a green Arabia indicates that human dispersal out of Africa might have been aided by this enhanced summer rainfall, leading migrating humans to colonise not only the woodlands of the Levant that were sustained by winter rainfall, but also such semi-arid grasslands in the Arabian interior as Al Wusta.
The site of the discovery, Al Wusta, is an ancient freshwater lake located in what is now the hyper-arid Nefud desert. Numerous animal fossils, including those of hippopotami and tiny freshwater snails were found at Al Wusta, as well as abundant stone tools made by humans.
To reach to their findings, the researchers used radiometric dating on the bone to determine its date.
One of the findings of the study was a well preserved and small fossil, just 3.2 cm long, which was immediately recognised as a human finger bone.
The researchers scanned the found bone in three dimensions and compared its shape to various other finger bones, both of recent Homo sapiens individuals, bones from other species of primates, and those of other forms of early humans such as Neanderthals. The results conclusively showed that the finger bone, the first ancient human fossil found in Arabia, belonged to our own species.
Using a technique called uranium series dating, a laser was used to make microscopic holes in the fossil and measure the ratio between tiny traces of radioactive elements. These ratios revealed that the fossil was 85,000 years old, according to a statement from the Max Planck Institute. Other dates obtained from associated animal fossils and sediments converged to a date of approximately 90,000 years ago.
Further environmental analyses also revealed the site to have been a freshwater lake in an ancient grassland environment far removed from today’s deserts.
Lead author of the paper Huw Groucutt, from the University of Oxford and the Max Planck Institute for the Science of Human History, said, “this discovery for the first time conclusively shows that early members of our species colonised an expansive region of southwest Asia and were not just restricted to the Levant. The ability of these early people to widely colonise this region casts doubt on long held views that early dispersals out of Africa were localised and unsuccessful.”
Project leader Michael Petraglia from the Max Planck Institute explained, “the Arabian Peninsula has long been considered to be far from the main stage of human evolution. This discovery firmly puts Arabia on the map as a key region for understanding our origins and expansion to the rest of the world. As fieldwork carries on, we continue to make remarkable discoveries in Saudi Arabia.”