More than a century ago, a skull was pulled from a riverbank in northeastern China. For decades, it sat hidden in a well—forgotten, unknown. The man who found it feared it would fall into the wrong hands during the Japanese occupation. He also hid it from the Chinese Communist authorities. It was only in 2018, on his deathbed, that he revealed its secret.

That cranium, nicknamed “Dragon Man,” was hailed as a momentous discovery. It appeared to be a new type of humanoid, one closely related to Neanderthals. Now, thanks to tiny traces of ancient molecules embedded in hardened dental plaque, scientists have a different conclusion. The skull belonged to a Denisovan — an elusive group of ancient humans known until recently only through DNA extracted from fragmentary remains in a Siberian cave.

With this, the Denisovans finally have a face. Or do they?

A ghostly human ancestor gets a face

For years, Denisovans have lingered at the edges of scientific understanding. They were first discovered in 2010 through DNA from a finger bone in Siberia’s Denisova Cave. Their DNA has been found in people living today in Southeast Asia and Melanesia, hinting at past interbreeding. In fact, the only known first-generation hominin hybrid is a Neanderthal-Denisovan girl named Denny.

But beyond scattered fingers and teeth, we had no idea what Denisovans looked like. Until now.

The new study, published in Cell by Qiaomei Fu and colleagues, is the first to definitively link a nearly complete human skull to Denisovan DNA. That skull, called the Harbin cranium, is over 146,000 years old and one of the best-preserved ancient human fossils ever found.

Getting DNA from this type of fossil is rarely easy. When Fu’s team set out to analyze the Harbin fossil, they first tried to extract DNA from the dense petrous bone and tooth. Nothing came out.

So then, they turned to a more creative approach. They looked to dental calculus, the mineralized plaque that forms on teeth. Though it might seem unpromising, this tartar can sometimes shield DNA from degradation. Lo and behold, this was the case here.

From just 0.3 milligrams of plaque scraped off a tooth, they were able to recover enough fragments of mitochondrial DNA to piece together a genetic fingerprint. That fingerprint aligned squarely with early Denisovans from Siberia, particularly those dating back over 150,000 years. The cranium’s DNA did not match Neanderthals or modern humans.

Dragon Man was Denisovan.

What did Denisovans look like?

The Harbin cranium suggests Denisovans were big and muscular. With a brain size comparable to modern humans and Neanderthals (around 1,420 cubic centimeters), the skull features include a broad face, large eye sockets, and heavy brow ridges. Overall, the fossil paints a picture of a powerful, robust human. The Harbin skull’s mosaic of traits — some primitive, others more evolved — reveals that Denisovans were a highly distinctive human lineage, bridging older hominin forms and our own species.

That might explain why their teeth, the most common Denisovan fossils, are so large. But it also raises questions. Why were they so big? Neanderthals are thought to have evolved stocky frames to withstand European cold. But Denisovan fossils have turned up in tropical Taiwan and high-altitude Tibet.

For now, it’s still too early to draw any conclusions about what this means. The researchers didn’t even look at nuclear DNA, only at mitochondrial DNA. Mitochondrial DNA (mtDNA) is inherited only from the mother and found in the cell’s mitochondria, providing information about maternal ancestry. Nuclear DNA is found in the cell nucleus, inherited from both parents, and contains the vast majority of an individual’s genetic information.

And even this was extremely difficult to get. The team used special techniques to minimize contamination, targeting ultrashort fragments of mitochondrial DNA that showed signs of ancient damage—a telltale mutation at their ends. They filtered out modern human contamination. Even so, not everyone is convinced.

Xijun Ni of the Institute of Vertebrate Paleontology and Paleoanthropology, who was not involved with the study, told Science News that their results may have been compromised by genetic contamination and interbreeding.

We have some clues into what Denisovans were like, but plenty of questions still abound.

Understanding Denisovans

Until now, Denisovans have been what scientists call a “ghost lineage” — known more from genetic echoes than physical remains. Their DNA has been found in everything from cave sediment to the genomes of modern people. But their bones, especially complete ones, have remained elusive.

The Harbin skull changes that, if it is indeed Denisovan. It also offers a new perspective on how to study them.

The researchers believe that several other fossils already in museum collections might be Denisovan. They’re also optimistic that more ancient DNA can be found — not just from bone, but from dental calculus and even sediment.

Meanwhile, we’re left to wonder what these humans were like — not just in body, but in mind. They had brains as big as ours, after all. Did they have language? Art? How did they interact with the modern humans and Neanderthals they shared the continent with? How did they interbreed with Neanderthals, and even Homo sapiens?

As more discoveries come in, the ghost of the Denisovans continues to take shape.

The study was published in Cell.