A skull found in a cave in Romania includes features of both modern humans and Neanderthals, possibly suggesting that the two may have interbred thousands of years ago.
Neanderthals were replaced by early modern humans. Researchers have long debated whether the two groups mixed together, though most doubt it. The last evidence for Neanderthals dates from at least 24,000 years ago.
The skull was found in Pestera cu Oase - the Cave with Bones - in southwestern Romania, along with other human remains. Radiocarbon dating indicates it is at least 35,000 years old and may be more than 40,000 years old.
The researchers said the skull had the same proportions as a modern human head and lacked the large brow ridge commonly associated with Neanderthals. However, there were also features that are unusual in modern humans, such as frontal flattening, a fairly large bone behind the ear and exceptionally large upper molars, which are seen among Neanderthals and other early hominids.