The discovery of a huge fossilised skull that was wrapped up and hidden in a Chinese well nearly 90 years ago has forced scientists to rewrite the story of human evolution.

Analysis of the remains has revealed a new branch of the human family tree that points to a previously unknown sister group more closely related to modern humans than the Neanderthals.

The extraordinary fossil has been named a new human species, Homo longi or “Dragon man”, by Chinese researchers, although other experts are more cautious about the designation.

“I think this is one of the most important finds of the past 50 years,” said Prof Chris Stringer, research leader at the Natural History Museum in London, who worked on the project. “It’s a wonderfully preserved fossil.”

The skull appears to have a remarkable backstory. According to the researchers, it was originally found in 1933 by Chinese labourers building a bridge over the Songhua River in Harbin, in China’s northernmost province, Heilongjiang, during the Japanese occupation. To keep the skull from falling into Japanese hands it was wrapped and hidden in an abandoned well, resurfacing only in 2018 after the man who hid it told his grandson about it shortly before he died.

An international team led by Prof Qiang Ji at the Hebei Geo University in China drew on geochemical techniques to narrow down when the skull came to rest in Harbin, dating the bones to at least 146,000 years old. The skull has a unique combination of primitive and more modern features, with the face, in particular, more closely resembling Homo sapiens. One huge molar remains.

The skull, which is 23cm long and more than 15cm wide, is substantially larger than a modern human’s and has ample room, at 1,420ml, for a modern human brain. Beneath the thick brow ridge, the face has large square eye sockets, but is delicate despite its size. “This guy had a huge head,” said Stringer.

The researchers believe the skull belonged to a male, about 50 years old, who would have been an impressive physical specimen. His wide, bulbous nose allowed him to breathe huge volumes of air, indicating a high-energy lifestyle, while sheer size would have helped him withstand the brutally cold winters in the region. “Homo longi is heavily built, very robust,” said Prof Xijun Ni, a paleoanthropologist at Hebei. “It is hard to estimate the height, but the massive head should match a height higher than the average of modern humans.”

To work out where the Harbin individual fitted into human history, the scientists fed measurements from the fossil and 95 other skulls into software that compiled the most likely family tree. To their surprise, the Harbin skull and a handful of others from China formed a new branch closer to modern humans than Neanderthals.

The Chinese researchers believe the Harbin skull is distinct enough to make it a new species, but Stringer is not convinced. He believes it is similar to another found in Dali county in China in 1978.

“I prefer to call it Homo daliensis, but it’s not a big deal,” he said. “The important thing is the third lineage of later humans that are separate from Neanderthals and separate from Homo sapiens.” Details are published in three papers in The Innovation.

Whatever the name, one possibility is that the Harbin skull is Denisovan, a mysterious group of extinct humans known largely from DNA and bone fragments recovered from Siberia. “Certainly this specimen could be Denisovan but we have to be cautious. What we need is much more complete skeletal material of the Denisovans alongside DNA,” Stringer said.

 

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Prof John Hawks, a paleoanthropologist at the University of Wisconsin-Madison, said the idea of a new lineage of humans was “a provocative claim”, because skulls can look similar even among distant relatives. The skull being Denisovan was a good hypothesis, he added, though he was less keen on a new species name. “I think it’s a bad moment in science to be naming new species among these large-brained humans that all interbred with each other,” he said. “What we are repeatedly finding is that the differences in looks didn’t mean much to these ancient people when it comes to breeding.”

Mark Maslin, a professor of earth system science at UCL and the author of The Cradle of Humanity, said: “The beautifully preserved Chinese Harbin archaic human skull adds even more evidence that human evolution was not a simple evolutionary tree but a dense intertwined bush. We now know that there were as many as 10 different species of hominins at the same time as our own species emerged.

“Genetic analysis shows that these species interacted and interbred – our own genetics contain the legacy of many of these ghost species. But what is a sobering thought, is that despite all this diversity, a new version of Homo sapiens emerged from Africa about 60,000 years ago which clearly out-competed, out-bred, and even out-fought these other closely related species, causing their extinction. It is only by painstaking searching and analysis of their fossils, such as the Harbin skull, do we know of their existence.”