A 30-year-old woman who died at least 9,900 years ago in Mexico has reshaped the understanding of how humans moved to the Americas.
The woman was found in an underwater cave known as Chan Hol near the Mexican city of Tulum when she was found by two divers.
Her skull was smashed but experts are unsure if this is the cause of death.
But the shape of her skull is very different to other humans who are known to have lived in the region at this time, shortly after the end of the last ice age.
Experts believe this is proof not all ancient people in the Americas entered the region as a singular population, as the traditional theory dictates.
Instead, it points to a radical new idea that at least two two physically different groups reached the American continent from different geographical points of origin.
Analysis of the remains suggests there may have been multiple groups of early American settlers.
According to the researchers, the skeleton, named Chan Hol 3, belonged a 30-year-old Paleoindian woman.
She was buried in the cave but it only became flooded around 2,000 years after she died due to rising sea levels.
Paleoindians were the first peoples to arrive, and subsequently inhabit, the Americas.
The woman’s remains were recovered by Mexican divers Vicente Fito and Iván Hernández and is the tenth skeleton to be found in the underwater cave system.
Not all of the ten skeletons were complete, but they were well preserved and his allowed for comprehensive analysis.
The scientists published their research in the journal Plos One and it revealed Chan Hol 3 had a round head with broad cheekbones and a flat forehead.
These features are similar three other skulls also from the Tulum caves.
However, her cranial characteristics are different to the long-headed Paleoindian skeletons found elsewhere in the region.
Dr Silvia Gonzalez a professor of geology at Liverpool John Moores University, said: ‘The Tulum skeletons may indicate that either more than one group of humans originally reached the American continent from different geographical points of origin, or that there was sufficient time for a small group of early settlers living in isolation on the Yucatan Peninsula, to develop a different skull morphology.
‘In either case, the early settlement history of the Americas appears to be more complicated and may date back thousands of years earlier than commonly believed, according to the new human morphology data.’
It is believed Paleoindians —literally meaning stone-age native Americans — journeyed across an ancient land bridge connecting Asia to North America, known as Beringia, during the last Ice Age more than 12,000 years ago.
They then migrated to the Patagonian region in South America.
The researchers say the shape and structure of the Chan Hol 3 skull is different to some of the other skeletons from a similar time period on the continent.
This, they say, indicates the existence of at ‘least two morphologically different Paleoindian populations’.
Dr Silvia Gonzalez a professor of geology at Liverpool John Moores University, and one of the study authors, told the PA news agency: ‘The new results are important because they question the “traditional model” for the peopling of the Americas with one single and homogeneous Paleoindian population migrating very fast from Beringia to Patagonia after 12,000 years ago.
‘Our results indicate that at least two morphologically different Paleoindian populations were coexisting in Mexico between 12,000 to 8,000 years ago, one in Central Mexico and the other in the Yucatan Peninsula.’
The team, led by Professor Wolfgang Stinnesbeck from Heidelberg University, dated the skeletal remains using mineral deposits called flowstone.
These form a lime crust which covered some finger bones.
Uranium-Thorium dating was used to determine the age of the skeleton and found it was, at the very youngest, 9,900 years old but likely to be over 10,000 years old.