In 2018, a child living in the village of Long Gua Pa in northeastern Laos approached a team of archaeologists, eager to show them a cave full of bones. The team began to chisel into the cave’s cementlike walls, exposing the remains of ancient rhinoceroses, tapirs, pigs, rodents—and a single, humanlike molar. Now, the researchers have identified the tooth as that of a Denisovan, mysterious cousins of Neanderthals and modern humans who likely died out about 30,000 years ago. The new find is the first fossil evidence of Denisovans in Southeast Asia—and it supports clues in the DNA in modern Indigenous populations that these ancient people once roamed the region.
“We have assumed that Denisovans were in Southeast Asia … but we just didn’t have the fossils for it,” says Bence Viola, a paleoanthropologist at the University of Toronto who has analyzed Denisovan teeth but was not involved in the new study. “This one is in the right place at the right time.”
Denisovans coexisted in Eurasia with Neanderthals beginning hundreds of thousands of years ago, and later with anatomically modern Homo sapiens as well. Although traces of their DNA live on in several modern populations—most notably in one group of Indigenous Filipinos who inherited about 5% of their genome from Denisovans—fossil evidence of their existence has been hard to come by. Researchers have uncovered a few teeth, a finger bone, and a piece of skull from Denisova Cave in Siberia, and a mandible with a pair of intact molars in Xiahe Cave on the Tibetan Plateau. Despite the genetic clues that Denisovans at one point dwelled in Southeast Asia, no fossils have turned up there.
The archaeologists who were led to the cave in 2018 had been excavating early modern human sites in Laos’s lush Annamite Mountains for 15 years. Now, in the depths of Cobra Cave, also known as Tam Ngu Hao 2, they dissolved rocky accretions around the mysterious tooth. The researchers pegged it as a permanent lower hominin molar. But from which species?
“We knew it looked kind of human, but not quite right for a modern human,” says Laura Shackelford, a paleoanthropologist at the University of Illinois, Urbana-Champaign, and senior author of the new study. It was much bigger, and the thickness of its enamel was distributed differently. Its pattern of ridges and hills didn’t match that of modern humans, either.
Study co-author Clément Zanolli, a paleoanthropologist at the University of Bordeaux and a dental structure expert, helped eliminate a few other possibilities: The molar was too big to have come from the diminutive island-dwelling humans H. floresiensis or H. luzonensis; its crown was too complex to belong to H. erectus. It looked a bit like a Neanderthal molar, but there is no genetic or fossil evidence that Neanderthals ever lived in Southeast Asia.
The researchers digitized the strange tooth using an x-ray scanner at the Max Planck Institute for Evolutionary Anthropology, precisely measuring its cusps, ridges, and crests. Next, they compared those measurements with the teeth of other humans and great apes. They found it most closely matched the lower molars on the Denisovan mandible from Xiahe Cave, they report today in Nature Communications.
The team used a variety of techniques to date the sediment in which the molar was found, as well as the animal bones alongside it, and determined the molar was deposited in the cave sometime 130,000 to 160,000 years ago, making it roughly the same age as the Xiahe Cave mandible.
Because of the tooth’s extreme age and the region’s hot, tropical climate, its ancient DNA was unlikely to be salvageable. Instead, the researchers took small chips of tooth enamel and analyzed them for the presence of ancient proteins; these are hardier than DNA but offer less precise answers about ancestry and other characteristics. The makeup of the Lao molar’s proteins confirmed it came from a member of our genus Homo, Shackelford says, and suggested its owner was most likely female. The tooth’s incompletely formed root and lack of wear indicates it hadn’t yet erupted, suggesting its owner was probably a juvenile when she died.
Shara Bailey, a dental paleoanthropologist at New York University, says she’s “sufficiently convinced” the tooth is Denisovan. She hopes other examples of Denisovan teeth will turn up in the collections of universities and museums, helping pin down the group’s impressive geographic range. “You can start building a picture of just how adaptable this group was,” Bailey says. “They lived in Siberia, they lived at high altitude, they lived in tropical forests. That’s pretty amazing.”
Science, 17 May 2022