In a cave in the north of Laos, researchers have unearthed a 164,000 to 131,000-year-old tooth that probably came from a Denisovan girl. If this assignment is finally confirmed, the find would be the first anthropological evidence that the Denisovans actually lived in Southeast Asia. They are an extinct human form that existed at the same time as Neanderthals and anatomically modern humans.
The second Denisovaner fossil, which was discovered outside of Siberia, is only the second Denisovaner fossil, which was recently presented in "Nature Communications". The site in Laos now underpins the thesis that the human form roamed in a much larger area than the previous bone and dental finds had been accepted.
"We always assumed that the Denisovans lived in this part of the world, but we had no direct evidence of this, " says Laura Shackelford, a paleoanthropologist at the University of Illinois Urbana-Champaign and co-author of the study. "This is now a small proof that they were really there.«
The eponymous Denisova Cave is where the majority of finds from Denisovan are found.
The Denisovans were first identified in 2010, when scientists sequenced the DNA of a finger bone from the Denisova Cave in Siberia and proved that it belonged to a previously unknown human form. Subsequent genetic studies have shown that the current population in Asia and Oceania contains fragments of Denisova genetic material.
So far, only genetic analyzes had shown that Denisova people were widespread far beyond Siberia. Fossil finds, on the other hand, are in short supply. They are limited to some teeth, bone splinters and a jawbone found in Tibet. Except for the fossil in Tibet, all copies come from the eponymous Denisova cave-including a piece of bone from a girl whose mother was Neanderthal and his father Denisovan.
That the find is so sparse is partly due to the fact that fossils are better preserved in cold and dry conditions than in warm, humid environments. Shackelford and her colleagues nevertheless searched for possible excavation sites in northern Laos in 2018, where they came across a cave called Ngu Hao 2, which was "full of teeth." These came from various animal species such as giant apirs, deer, pigs and ancestors of today's elephants. Porcupines probably collected the pieces to sharpen their own teeth and gain nutrients, Shackelford explains. One of the first fossil finds from the cave was a small, not fully developed tooth of a hominin.
Why it might be a denisovan tooth
A dating of the cave rock and animal teeth showed that the human tooth is older than the remains of the first anatomically modern people in this region. "It was a huge surprise," says Shackelford. The working group hadn't expected to encounter human remains at all. Initially, the researchers assumed that the tooth came from a homo erectus. This form of man lived in Asia about 2 million to 100,000 years ago. But the molar is "too complex" for Homo erectus, find Shackelford and her team. And although some characteristics are reminiscent of the teeth of Neanderthals, the molar is striking "big and somehow strange," says Bence Viola, paleoanthropologist at the University of Toronto.
The greatest similarity is with the teeth in Tibet's jawbone. "Denisovans had absolutely gigantic teeth," says Viola. "So it is very likely a Denisovan."
The tooth root at the find from Laos is not fully trained, which indicates that the tooth belonged to a child. In addition, certain peptides that are connected to the Y chromosome were missing in the tooth enamel-an indication that the molar could come from a female Denisovan.
Was that a Denisovan, really?
To reconstruct an entire human form from bone fragments that have been decomposed for millennia under tropical conditions is quite difficult, says Katerina Douka from the University of Vienna. As long as you can no longer find fossils or carry out other DNA analyzes, "we cannot really know whether this individual and poorly preserved molar has ever belonged to a Denisovan."
For Bence Viola, on the other hand, the molar was "in the right place at the right time" to belong to a Denisovan. If confirmed, it would be clear: The human form could adapt to different environmental conditions. More than 131,000 years ago, the region in Laos was slightly forested and the climate temperate – so conditions were very different from those in Siberia and Tibet, where the Denisovans had to withstand icy temperatures. The fact that they could live in different climate zones would also distinguish Denisovans from Neanderthals and move closer to Homo sapiens. Because the Neanderthals were mainly adapted to colder places.
Although the tooth cannot be assigned to a certain human form at the moment, the find may encourage other researchers to search for fossils of prehistoric humans in Southeast Asia; Viola is convinced of this. "When we started doing research in Laos, everyone thought we were crazy," says Shackelford. "But if we can find things like this tooth – which we didn't expect – then there are probably more hominin fossils to be discovered.«
