Fossilized 'Dragon Man' Skull May Represent a New Lineage of Extinct Humans

(Inside Science) -- A fossilized skull from China may belong to a new human lineage, new research suggests. Nicknamed "Dragon Man," this newly identified group may have had the largest skulls of any known extinct human lineage, and it may belong to a mysterious branch of humanity found across Asia and currently known only from teeth, bone scraps and DNA.

The skull was reportedly unearthed during construction work in 1933 when a bridge was built over the Songhua River in the northeastern Chinese city of Harbin. The exact site of the find remains uncertain due to the long, confusing history since its discovery.

The fossil, which is at least 146,000 years old, is one of the most complete ancient human skulls in the world. It could have housed a brain comparable in size to a modern human's, but it had larger, almost square eye sockets, thick brow ridges, a wide mouth and oversized teeth.

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All in all, a new analysis suggests the skull, currently the only known specimen of this lineage, combines a mix of ancient and more recent human features that sets it apart from any previously known members of Homo, the genus name of the human family tree, said paleontologist Qiang Ji at Hebei GEO University in China. Ji is a lead author of one of three studies appearing today in the journal The Innovation.

"It's obviously surprising and exciting that a skull dredged up almost 90 years ago turns out to be a major discovery -- it makes you wonder what else there might be in museum basements," said paleoanthropologist Robin Dennell at the University of Sheffield in England, who did not take part in this research.

The research team's analysis of more than 600 of the skull's features suggested it belonged to a third human lineage that coexisted with but was distinct from both modern humans and Neanderthals. Other ancient human fossils unearthed in China at sites such as Dali, Jinniushan, Xiahe and Hualongdong may belong to the same group, said Chris Stringer, who is a paleoanthropologist at the Natural History Museum in London and a co-author of two of the new studies.

The researchers suggested the skull came from a roughly 50-year-old man who lived in a forested floodplain as part of a small community. The community members could have hunted mammals and birds, gathered fruits and vegetables, and perhaps caught fish, said paleoanthropologist Xijun Ni at Hebei GEO University, a lead author on one of the three studies.

The scientists gave their discovery the new species name of Homo longi. "Long" means dragon in Chinese. The name of the province in which the skull was found -- Heilongjiang -- literally means "black dragon river." 

However, not every scientist agrees that Dragon Man should be considered a different species from modern humans. For instance, "Neanderthals and modern humans look very different, but could still interbreed and produce fertile offspring, so there is no reason to consider them different species," said paleoanthropologist Israel Hershkovitz at Tel Aviv University, who was not part of this work. 

Instead of falling into an entirely new category, Dragon Man may potentially belong to an extinct human lineage known as the Denisovans, which previous ancient DNA research suggested were a sibling group to modern humans and Neanderthals. Both Denisovans and Neanderthals interbred with Homo sapiens and left a genetic legacy throughout modern humans in Asia. Direct knowledge of the Denisovans currently comes only from DNA and proteins from teeth and bone scraps in Siberia, and from a jawbone from the high Tibetan plateau.

"We've established an Asian lineage based on fossils, and Denisovans are an Asian lineage based on DNA. And it'd make things much simpler if we could show they were one and the same thing," Stringer said. "But we can't establish that yet without a really complete fossil with a complete genome."

A number of anatomical features tantalizingly suggest Dragon Man may be a Denisovan, such as extremely large molars and the lack of a third molar, Stringer said. "I think I'd stick my neck out and propose that [the skull] is Denisovan until otherwise proven," Dennell said. Paleoanthropologist Matthew Tocheri at Lakehead University in Canada, who did not participate in this study, agreed, saying, "If it walks like a Denisovan and talks like a Denisovan..."

The scientists' analysis suggests Dragon Man may be even more closely related to modern humans than Neanderthals are, making it our closest known relative, Ni said. However, "I think that's a stretch," Tocheri said. For example, Tocheri noted that some of the facial features used to suggest a special connection between modern humans and Dragon Man are in fact ancient traits modern humans are thought to share with the last common ancestor we had with Neanderthals and Denisovans.

If this fossil does turn out to belong to a Denisovan, previous analysis of Denisovan DNA would suggest Dragon Man may not be any more closely related to modern humans than Neanderthals are, Stringer acknowledged. "We have to resolve this with more data," Stringer said.

Given the likely size of this ancient human and where it was found, the researchers suggest it was adapted for harsh cold. "Harbin, where the skull was found, experiences some of the coldest winters in China, has the biggest ice festival in China, and it was possibly even colder when this individual was alive than today," Stringer said. "Its size could have been an adaptation to this climate -- the nearer to the poles that mammals get, the larger their body size tends to be to help conserve heat."

It is difficult to say why the skull's eye sockets were nearly square. "The whole skull is large, so it may be due to that," Stringer said. "Also, living further north, maybe it experienced darker conditions and so had larger eyes to adapt. But we're not really sure right now. It'd be interesting to see if you see a matching size in the visual lobes of the brain."

Future research may extract proteins or DNA from the Harbin skull to help pinpoint its place in the human family tree. "My Chinese colleagues want to move cautiously here -- they don't want to destroy valuable parts of this fossil unless they can be confident of results," Stringer said. Infrared scans could reveal where organic molecules could be preserved in the skull, he noted.