In 1980, a Buddhist monk found the right half a fossilized hominin jawbone in Baishiya Karst Cave on the Tibetan Plateau, Xiahe, China. An analysis of ancient proteins extracted from the fossil — dubbed Xiahe mandible — shows that it belonged to a member of the mysterious human-like group known as Denisovans. It is the first Denisovan specimen found outside the remote Denisova Cave.
Denisovans were probably dark-skinned, unlike the pale Neandertals. The picture shows a Neanderthal man. Image credit: Mauro Cutrona.
Denisovans are an extinct sister group of Neanderthals and are known from fragmentary fossils from Denisova Cave in the Altai Mountains of Siberia. Their genomic legacy is present in several Asian, Australian and Melanesian populations, which suggests that they once might have been widespread.
The Xiahe mandible provides direct evidence of the Denisovans outside the Altai Mountains.
“Our analysis shows that the Xiahe mandible belonged to a hominin population that was closely related to the Denisovans from Denisova Cave,” said co-author Dr. Frido Welker, a researcher with the Max Planck Institute for Evolutionary Anthropology, the University of Copenhagen and Lanzhou University.
While Dr. Welker and colleagues could not find any traces of DNA preserved in this fossil, they managed to extract ancient proteins from one of the molars.
“The ancient proteins in the mandible are highly degraded and clearly distinguishable from modern proteins that may contaminate a sample,” he said.
The Xiahe mandible with adhering carbonate crust. Image credit: Chen et al, doi: 10.1038/s41586-019-1139-x.
Attached to the mandible was a heavy carbonate crust, and by applying U-series dating to the crust the team found that the mandible is at least 160,000 years old.
“This minimum age makes the Xiahe mandible comparable in age to Denisova 2, chronologically the oldest Denisovan fossil that is currently known from Denisova Cave,” said co-author Dr. Chuan-Chou Shen, a scientist in the Department of Geosciences at National Taiwan University.
“The Xiahe mandible represents the earliest hominin fossil on the Tibetan Plateau. It is at least 120,000 years older than the oldest known Paleolithic sites in the region,” said first author Dr. Fahu Chen, Director of the Institute of Tibetan Research.
Denisovan introgression into present day Tibetans, Sherpas and neighboring populations includes the Denisovans’ version of the EPAS1 (endothelial PAS domain-containing protein 1) gene, which provides high-altitude adaptation to hypoxia in humans who inhabit the Tibetan Plateau.
“The Xiahe mandible demonstrates that Denisovans or Denisovan-related populations occupied the Tibetan Plateau and successfully adapted to high-altitude hypoxic environments long before the regional arrival of modern Homo sapiens,” the researchers said.
The findings were published in the journal Nature.
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Fahu Chen et al. A late Middle Pleistocene Denisovan mandible from the Tibetan Plateau. Nature, published online May 1, 2019; doi: 10.1038/s41586-019-1139-x
