‘Dragon Man’ skull may be new species, shaking up human family tree

Hidden down a well for decades, the stunningly complete cranium is stirring debate about the increasing number of fossils that don’t neatly fit in the classic human origin story.

Published 28 Jun 2021, 10:42 BST
Dragon Man Reconstruction

The Dragon Man lived more than 146,000 years ago in a chilly region in northeastern China, as depicted in this reconstruction.

Photograph by Illustration by Chuang Zhao

The strange skull appeared soon after the Japanese invaded northeast China in the early 1930s. A team of locals was raising a bridge near Harbin, a city in China’s northernmost province, when one of the workers stumbled on a surprise in the river mud. The nearly complete human skull had an elongated cranium from which a heavy brow bone protruded, shading the gaping squares that once housed eyes.

And then there was the skull’s unusual size: "It's enormous," says palaeoanthropologist Chris Stringer of London's Natural History Museum.

Perhaps aware of the magnitude of the find, the man secreted the skull away in an abandoned well. Now, nearly 90 years later, a study published in the journal The Innovation makes the case that this skull represents a new human species: Homo longi, or the Dragon Man.

Two additional studies reveal that the stunningly preserved cranium likely came from a male that died at least 146,000 years ago. Its mashup of both ancient and more modern anatomical features hints at a unique placement on the human family tree.

"I’ve held a lot of other human skulls and fossils, but never like this," says palaeoanthropologist Xijun Ni of the Chinese Academy of Sciences, who is an author of all three studies.

Based on the shape and size of the Harbin skull, as it's often called, and comparison to other known fossils, the researchers posit that it’s closely related to several other perplexing human fossils, from this same time period, that have been found across Asia. The researchers’ analysis suggests all these fossils belong to a group that is closely related to our own species—perhaps even more so than the Neanderthals.

"It's a spectacular fossil," says María Martinón-Torres, the director of Spain's National Research Centre on Human Evolution, who was not involved in the suite of papers.

Yet the proposed grouping and species designation is stirring debate among scientists. Some experts see tantalising hints that the Dragon Man may have ties to the mysterious Denisovans, a sister group of the Neanderthals for which scant fossil remains have been found—a few teeth, a fractured piece of skull, a pinky bone, and perhaps a broken jaw.

While she is excited about the Harbin skull’s preservation and mosaic of features, "at this point, I am not that clear how different it is from other groups that are already known," Martinón-Torres says.

Still, the skull underscores how tangled the branches are in the human family tree, and how studying the full array of enigmatic human ancestors and their shifting distribution through time could help us decipher our own origins.

"We forget, even as anthropologists, that it’s really weird for us to be the only hominins left alive," says Laura Buck, biological anthropologist at Liverpool John Moores University, who was not part of the study team.

Story from the skull

Before his death, the worker who found the skull disclosed his long-held secret to his grandchildren, who ventured to the well to retrieve the prize in 2018. Qiang Ji, a palaeontologist at Hebei GEO University of China who led the new research, caught wind of the find and went to take a look. Unsure of its significance, he took a picture to show Ni.

"I was shocked," Ni recalls. Not only was the fossil remarkably well preserved, it sported that odd mishmash of features. The Harbin skull is squat and wide, with a prominent brow common among ancient hominins. Only one tooth remains in the jawless cranium, but that tooth has three roots, which is a rare trait among modern humans. Other features—such as its delicate cheekbones, which sit flat and low on the face—are more reminiscent of our own species.

"You have a very strange feeling when you look into the eye sockets," Ni says. "You're always thinking, he's trying to tell you something."

Ji persuaded the family to donate the specimen to the Geoscience Museum of Hebei GEO University, and the team got to work. They accrued information from 95 fossil crania, jawbones, and teeth representing a range of hominin groups, characterising more than 600 features. They then used a supercomputer to construct billions of phylogenetic trees, tools used to illuminate the evolutionary relationships between hominins, with the fewest evolutionary steps, which most scientists agree is the most likely possibility. The tree that sprouted placed the Harbin skull on a new branch that is closely related to our own species.

"I was surprised to see this," says Stringer, who is an author on two of the studies defining the grouping and age of the fossil. He had expected the Harbin skull to be an offshoot of the Neanderthals.

The Harbin cranium, with its combination of both ancient and modern features, joins a growing number of fossil finds across Asia that don’t neatly fit on the branches of the human family tree.
Photograph by Image by Xijun Ni

Part of the team thought that the Harbin skull was so different from other hominin fossils that it should be named a separate species. Ni, an author on the third study defining the new species, ticks off the list of features that together define the Dragon Man: remarkably square eye holes, a long and low braincase, lack of a ridge along the skull's midline, and more.

"It's not just one feature that distinguishes this from all the others," he says. "It's kind of a combination."

Debating the Dragon Man

Yet not all the scientists and outside experts agree that Dragon Man is a separate species—nor do they agree about its relative position on the hominin family tree.

Many of the skull's defining characteristics seem to be matters of scale rather than distinct features, says Buck, of Liverpool John Moores University. Even within a species, she says, some variation is expected. Differences in sex, age of the individual, regional adaptations, age of the fossil, and more can all drive slight individual changes.

If not its own species, what was the Dragon Man? Stringer points to a similar mix of modern and more ancient traits in a fossil called the Dali cranium, which the new study categorised in the same group as the Harbin skull. Found in Shaanxi Province in Northwest China, this skull is considered its own species, Homo daliensis.

"There is already a bit of an inflation of species names in anthropology," adds Bence Viola, a palaeoanthropologist at the University of Toronto, who was not part of the study team. He thinks it’s preferable to group the skull with H. daliensis, or leave the species unnamed, rather than coining a new species moniker.

Then there are the mysterious Denisovans. Though not formally recognised as its own species, this group likely inhabited Asia for tens of thousands of years, and many Asian fossils have been suggested as members. But because scientists have found only meagre fossil traces of their existence, genetic confirmation is necessary—and DNA preservation becomes increasingly unlikely with older fossils.

In 2019, scientists announced the discovery of a fractured jaw on the Tibetan Plateau that likely came from a Denisovan, which would make the bone the first fossil of these ancient humans found outside the cave that gives the group its name.

The newly proposed phylogenetic tree suggests the Dragon Man is most closely related to this jaw, called the Xiahe mandible.

"They probably belong to the same species," Ni says. But he's hesitant to call the jaw (and thus the Dragon Man) Denisovan, since the fractured mandible's identity came by way of proteins extracted from the jaw and DNA extracted from sediments, not directly from the mandible's DNA. The Harbin skull also lacks a jaw for physical comparison.

Viola, who was on the team that first described the Denisovans, disagrees, noting that Denisovan identity is most logical for the Xiahe mandible. But he points out that even if the Dragon Man was Denisovan, the new analysis places the branch of the tree that includes both the Harbin skull and the Xiahe mandible apart from the Neanderthals.

That would be odd, since such a grouping conflicts with the story of the Denisovans laid out in past studies of their genetics. Those analyses suggest that the common ancestor of Neanderthals and Denisovans split from the predecessors of Homo sapiens some 600,000 years ago. That ancestor then split into two groups, with Neanderthals fanning out through Europe and the Middle East and Denisovans moving into Asia.

The relationships between all these groups are "bound to be close and difficult to resolve," palaeoanthropologist Katerina Harvati, who was not part of the research, says via email. "I think probably this is something that will need to be worked out more closely once there is more evidence," says Harvati, of Eberhard Karls University of Tübingen.

Frozen dragons

More evidence may be on the horizon. The team involved in the new papers is exploring the possibility of genetic analyses for the Dragon Man, Ni says. But they are proceeding with caution because such work requires destroying small samples of the fossil.

Regardless of whether Dragon Man is a new species, its stunningly preserved features are a reminder that nature rarely paints inside the lines, and that categorisation will only get more complex as new discoveries emerge.

"What you consider a species is really this philosophical question rather than this biological truth," Buck says. Species definitions can be useful, she says, but "for me, the more interesting questions are ... how did they adapt? And how did they exist in the world?"

Here, too, the Dragon Man offers enticing possibilities. The exact location where the worker pulled it from the mud remains unknown, but the proposed region is extremely far north, says Michael Petraglia, a palaeoanthropologist at the Max Planck Institute for the Science of Human History, who was not part of the research. Even in today's relatively balmy conditions, the wintertime temperatures in this area can plummet below minus 12 degrees Celsius; about 146,000 years ago, it probably wasn’t much warmer.

The team speculates that some of the skull’s robust traits reflect adaptations to a much colder climate. The environment may have also isolated the Dragon Man and its kin from other hominins, Petraglia says, which could have driven some of the distinctiveness seen in the fossil today.

The team's full database and detailed images of the Dragon Man are now publicly available, Stringer says, so other researchers can plumb the hominin’s depths themselves. Many seem eager to do so.

As Sarah Freidline of the University of Central Florida says via email: "The completeness of the Harbin skull is every palaeoanthropologist's dream.”

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