ABOVE: The fossil tooth found in the Annamite Mountains in Laos F. Demeter et al., CC by 4.0

The molar of a Denisovan girl who lived more than 130,000 years ago may help answer how indigenous people living in Australia and other Pacific island nations share DNA with the early-human species. Until now, scientists haven’t understood how Denisovans, whose remains had previously been found only in western China and Siberia, contacted and interbred with modern humans who migrated east from Africa through Southeast Asia and settled in the southwest Pacific region. A new study, published yesterday (May 17) in Nature Communications, identifies a tooth found in Laos as Denisovan and bridges the geographical gap.

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Scientists unearthed the tooth in caves within the Annamite Mountains in northern Laos, where they suspected Denisovans could have crossed paths with modern humans before they reached the southwest Pacific.

“We knew that Denisovans should be here. It’s nice to have some tangible evidence of their existence in this area,” study coauthor Laura Shackelford, a paleoanthropologist at the University of Illinois, tells The New York Times.

Although the team of researchers started digging in Laos in 2008, they didn’t explore the cave where the tooth was found until 10 years later. Children from a local village guided Shackelford to the cave, where an initial peek inside didn’t reveal anything, according to the Times.

“But then I turned my flashlight on, and I looked up,” Shackleford tells the Times. “All you could see were bones and teeth, embedded in the walls and in the ceiling of this cave.” 

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While most of the recovered fossils were from nonhuman mammals, protein fragments taken from the enamel of a well-preserved tooth helped the team determine that it likely belonged to a girl who was between the ages of 3 1/2 and 8 1/2 years old. Luminescence dating of the debris that surrounded the tooth suggest the molar is between 134,000 and 161,000 years old.

The recovered protein groups from the girl’s tooth are common among early humans and could not help the researchers determine whether her lineage was modern human, Neanderthal, or Denisovan, the Times reports. To investigate the ancestral roots of the tooth, the researchers scanned it using X-ray microtomography, which enabled them to create high-resolution, three-dimensional representations that they then compared to teeth from other early-human fossils. The girl’s tooth so closely matched the morphology of a tooth from a Denisovan mandible found in China’s Gansu Province that the researchers concluded she was likely also Denisovan.

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Shara Bailey, a paleoanthropologist at New York University who has studied that mandible but was not involved in the new study, says she finds the study convincing. “I agree 100 percent with the analysis,” she tells the Times.

Researchers have found modern human skull fragments as old as 75,000 years from the network of caves in Laos, along with evidence that Denisovans occupied the surrounding area as recently as 50,000 years ago, the Times reports.