About 500,000 years ago, different members of the Homo genus spread throughout Europe and Asia, some of which evolved into the Neanderthals, the closest extinct relative of modern humans.

From what particular hominin species the Neanderthals evolved from, however, has been the subject of debates. Now, a newly discovered skull found in the cave of Aroeira in Portugal offers clues that may help solve the mystery of the Neanderthal ancestry.

400,000-Year-Old Skull

The skull represents the westernmost human fossils discovered in Europe during the middle Pleistocene epoch, which marks the appearance of fossil hominins to whom the Neanderthals later descended, and Acheulean technology.

It is one of the earliest to be linked to the Acheulean stone tool industry. Unlike other fossils from this same period, which are poorly dated or do not have clear archaeological context, the cranium is well-dated and associated with stone tools, which include hand axes and animal remains.

The skull was discovered in 2014 along with ancient stone hand axes. It was found to be 400,000 years old and belonged to an archaic member of the Homo, the genus that includes the species Homo sapiens, which includes modern humans.

As described in the study, which was published in the Proceedings of the National Academy of Sciences, the skull reveals a new mix of features that have not yet been observed in fossil humans. Scientists found that it has traits that link it to the Neanderthals, which include fused brow ridge and other primitive traits that are similar to other extinct fossils discovered in Europe.

"This is an interesting new fossil discovery from the Iberian Peninsula, a crucial region for understanding the origin and evolution of the Neandertals," said study researcher anthropologist Rolf Quam, from Binghamton University. "The Aroeria cranium increases the anatomical diversity in the human fossil record from this time period, suggesting different populations showed somewhat different combinations of features."

Researchers hope that with these new feature combinations on a well-dated skull, they will be able to sort out how different fossils in Europe are related to one another and which ones later evolved into the Neanderthals.

"Unlike most other Middle Pleistocene finds, which are of uncertain chronology, the Aroeira 3 cranium is firmly dated to around 400 ka and was in direct association with abundant faunal remains and stone tools," the researchers wrote in their study.

"The Aroeira cranium represents a substantial contribution to the debate on the origin of the Neandertals and the pattern of human evolution in the Middle Pleistocene of Europe."

The Neanderthals

Before they became extinct, the Neanderthals interbred with modern human ancestors thousands of years ago. New studies revealed that the genes of these archaic human cousins that interbred with our human ancestors still live on today and are responsible for some of our traits and chances of having diseases such as schizophrenia and lupus.

Interbreeding with Neanderthals also appeared to provide modern humans with some benefits such as having strong immune systems that can help with survival in tough environments.

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