A team of researchers unearthed the oldest fossil human cranium in Portugal, one that's found to exhibit characteristics similar to both Neanderthals and Homo erectus.

According to a report from Phys Org, this newly-found cranium in the cave of Aroeira in Portugal is the westernmost human fossil ever found in Europe during the middle Pleistocene epoch. It's also one of the earliest associatied with the Acheulean stone tool industry. While other fossils from this period are poorly dated with little to no archaeological context, this recent one is properly dated to 400,000 years ago with plenty of remains and tools.

"This is an interesting new fossil discovery from the Iberian Peninsula, a crucial region for understanding the origin and evolution of the Neandertals," Binghamton University associate professor of anthropology and one of the co-authors Rolf Quam explained. "The Aroeira cranium is the oldest human fossil ever found in Portugal and shares some features with other fossils from this same time period in Spain, France and Italy."

He added, "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."

His last point is significant, highlighting the fact that the individual cranium exhibited traits similar to Neanderthals and some that are more like the Homo erectus. A report from the Christian Science Monitor revealed that this isn't the first fossil to show a combination of traits as there have been others from Spain, France, Italy and Germany.

Erik Trinkaus, a paleoanthropologist at Washington University in St. Louis and one of the co-authors, calls it simply a "natural variation". This belief maintains that some groups of archaic humans would have completely uniform traits, while others could have interbred or developed a host of different traits.

Trinkhaus used gray wolves as an example with regional variations in coat colors and features - yet all considered one species. To the scientists, all archaic humans belong to a single species as well.

The team's findings were published in the journal Proceedings of the National Academy of Sciences.