A team of international researchers studying an ancient skull determined it belongs to a newly discovered species that’s more closely related to modern humans than Neanderthals, but others in the scientific community say the skull might belong to a mysterious, but already known ancestor.

The skull was reportedly found by a farmer in the northern Chinese city of Harbin during the early 1930s, while he worked on a labor crew that was building a bridge.

In 1933, the farmer hid the ancient skull inside a well, intending to keep it hidden from Japanese forces that occupied the city during World War II—fearing soldiers might loot it as a war treasure.

The skull would remain inside the well for the better part of a century, before the farmer reportedly told his grandchildren about the skull while on his deathbed in 2018. The skull was then located and given to a Beijing-area university.

If the skull does belong to a new species, it’s largely unclear what their lives looked like. It’s also unclear how much they might contribute to the lineage of modern humans.

“The DNA evidence suggests that if a hominin sees another hominin they’re happy to interbreed, even if their brow ridge is a little bigger or their skull is a little higher,” said Dr. Karen Baab, a Midwestern University anthropologist not ᴀssociated with the research, in The Wall Street Journal.

Research in the past few years has definitively linked Neanderthals with modern humans, with most findings showing Neanderthals make up about 2% of the DNA of Europeans and Asians—though some suggest the amount might be much higher. The DNA of Denisovans has also been found in small amounts in modern populations, particularly among Asians.