Scientists have firmly dated a 400,000-year-old skull fragment in Portugal, which could point to a previously unknown ancestor to the Neanderthals. 

The skull bears a mixture of traits—some link it to the Neanderthals, such as a fused brow ridge, while other features are representative of other extinct fossils in Europe, according to the journal Science.

Researchers made the discovery in 2014 in the Gruta da Aroeira cave in central Portugal and believe it is a member of the genus homo, according to the study published Monday in the journal Proceedings of the National Academy of Sciences (PNAS ).