Fossilized human skulls found in a cave in Greece may force a rewrite of the human migration timeline yet again. Archaeologists have dated one of the skulls to about 210,000 years old – roughly 150,000 years older than the previous record-holder for earliest modern human remains in Europe.

Two skulls were discovered in Apidima, southern Greece, way back in the 1970s, but they weren't able to be properly identified or dated. Now, a team of researchers from Greece, Germany, Australia and the UK has used modern dating and imaging techniques to figure out who they belonged to and how long they've been sitting there.

The results were surprising. The two skulls, dubbed Apidima 1 and 2, were from different species of human living at different times. Apidima 1 was determined to be a Homo sapiens specimen, characterized by the skull's rounded back. Certain more primitive features were mixed in too, but this is to be expected for its age – humans didn't reach "full modernity" until about 50,000 years ago.

Apidima 2, meanwhile, was unmistakably Neanderthal in origin. It had a thick, rounded brow ridge, and other minor characteristics of this related species.

But perhaps the most interesting thing about the two skulls is their ages. Although they were found in the same piece of rock, just 30 cm (12 in) apart, they were separated by roughly 40,000 years in time. Apidima 2 lived about 170,000 years ago – well within the time frame of Neanderthals in Europe – while Apidima 1 was dated to be 210,000 years old. According to the researchers on the new study, that makes Apidima 1 the oldest known fossil of modern humans in Europe.

The currently accepted story is that modern humans arose about 300,000 years ago, but were mostly constrained to Africa until roughly 120,000 years ago. That said, recent fossil finds in Israel suggest that modern humans had made it into West Asia as long as 177,000 years ago.

If the new fossils are confirmed to be as old as the researchers believe, they indicate that humans migrated out of Africa much earlier, and traveled further, than previously thought.

"Our results suggest that at least two groups of people lived in the Middle Pleistocene in what is now southern Greece: an early population of Homo sapiens and, later, a group of Neanderthals," says Katerina Harvati, lead researcher on the study. "The Adipima 1 skull shows an early dispersal happened earlier than we thought, and also reached further geographically, into Europe itself. We hypothesize that, as in the Near East, the early modern human population represented by Apidima 1 was probably replaced by Neanderthals, whose presence in southern Greece is well documented, including by the Apidima 2 skull from the same site."

So why were the two fossils, so far apart in time, stuck in the same rock? The team used laser ablation U-series dating to determine the age of the skulls and the breccia rock surrounding them, and found that the rock solidified about 150,000 years ago.

"The most likely scenario is that there were bone deposits elsewhere in the cave system and that some time around 150,000 years ago, these different deposits were washed down the solution pipe and ended up in the same solidified breccia," says Rainer Grün, another author of the study.

The research was published in the journal Nature.

View gallery - 2 images