Washington, Apr 10 (IANS): The first fossil of an ancient human found in the Arabian Peninsula could challenge a widely accepted theory of how modern humans migrated out of Africa, a study has shown.

A fossil finger bone found in the heart of Saudi Arabia -- in the middle of what is now called the Nefud Desert -- dates to at least 85,000 years ago, seemingly belonging to a member of the Homo sapiens species, CNN reported on Monday.

This fossilised bone, measuring just 3.2 cm in length, is the oldest directly dated Homo sapiens fossil discovered outside of Africa, according to the study published in Monday the journal Nature Ecology and Evolution.

"What our discovery shows is that the early spread of Homo sapiens was much more spatially widespread than we thought," said lead study author Huw Groucutt of the University of Oxford.

"These people were extending far into grasslands in the Arabian Peninsula."

This finding challenges the existing consensus view of modern human migration -- known as "Out of Africa" -- that indicates modern humans originated in Africa and migrated to the rest of the world in a single wave about 60,000 years ago.

This find suggests that instead of one rapid dispersal out of Africa, Homo sapiens were moving out of Africa multiple times, 20,000 to 25,000 years earlier than expected.

Today, the site, known as Al Wusta,is a hyper-arid desert, but environmental analyses revealed that it would have once been a perennial fresh-water lake in a semi-arid grassland setting, CNN reported.

Enhanced monsoonal rainfall transformed the Arabian Peninsula into an area covered with lakes and rivers when humans lived there 85,000 years ago.

Groucutt speculates that animals from sub-Saharan Africa would have migrated into the Sahara and out of Africa into Arabia, too.

"Naturally, hunter-gatherers would have followed," he said.

Over 800 animal fossils including gazelle, hippopotamus and wild cattle were excavated at the site.