A basic visual examination suggested it belonged to Homo sapiens, Groucutt said.
Two things make it unusually significant. Although it's a desert zone now, 90,000 years ago, the site was on the bank of a freshwater lake.
The study feeds into a long-running argument over the route humans took out of Africa. Previously discovered human fossils show an earlier human presence in Israel and possibly China. These ratios revealed that the fossil was 88,000 years old. In the Luna Cave, more teeth were uncovered among material that is believed to be between 130,000 and 70,000 years old. Hundreds of animal fossils were found at the site, including those belonging to hippopotamus, as well as plenty of stone tools made by humans.
The team of global researchers led by the Max Planck Institute for the Science of Human History was conducting archaeological fieldwork in the Nefud Desert of Saudi Arabia when they came across the striking fossil.
"They're coming up against animals that they've never seen before; environments they've never seen before", he said.
General view of the excavations at the Al Wusta site, Saudi Arabia.
Study co-researcher Iyad Zalmout, a paleontologist with the Saudi Geological Survey, found the remarkable 1.3-inch-long (3.2 centimeters) fossil finger in the Nefud Desert in 2016, said study lead researcher Huw Groucutt, an archaeologist at the University of Oxford in England.
The bone was checked in three measurements and its shape contrasted with different other finger bones, both of late Homo sapiens people and bones from different types of primates and different types of early people, for example, Neanderthals.
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Using a technique called uranium series dating, Grün was able to pinpoint how long the fossil had been buried.
However, even though the finger bone is much younger than the jawbone, it's still a momentous find, Groucutt said.
It was an intermediate phalanx, the bone between a fingertip and finger knuckle. While the Levant was then a wooded area with winter rainfall, Al Wusta, about 400 miles (650 kilometers) away, was a grassland that received summer rain.
"The Arabian Peninsula has always been considered to be far from the main stage of human evolution".
The findings demonstrate that climate change aided the spread of our species earlier than previously thought.
While it is not clear whether the finger bone is from a man or woman, how old they were when they died or which hand it is from, the team say a careful comparison showed the bone was from our own species and is probably the second bone from the end of the middle finger.
Today, this is where the Red Sea meets the Gulf of Aden.
"Tracing the evolution and geographic dispersal of the human lineage is rather like connecting pitifully few dots on a vast three-dimensional grid of time and space", Donald O. Henry, an anthropologist from the University of Tulsa, wrote in an article published alongside the new study.
Although tiny and seemingly insignificant, this finger fossil might be an important piece of the complex jigsaw puzzle that is the story of human dispersal out of Africa.