The Denisovans are the most enigmatic and mysterious of human ancestors, and also one of the most fascinating. Finds proving their existence have been incredibly rare, which is why the discovery of a new Denisovan fossil is always big news, and cause for celebration among those who study human evolution.
So let the celebration begin: scientists have just announced that a fossilized, human-looking jawbone found off the west coast of Taiwan in the early 2000s is in fact Denisovan. These human ancestors lived in Asia in more recent times, and the discovery of this fossil in this location shows they ranged far and wide across southern and eastern Asia between 370,000 and 30,000 years ago, despite leaving such a scarce collection of remains behind.
The truth about the Denisovan jawbone had been difficult to discern up until now. But in the new study, researchers used an innovative technique that analyzes protein sequences to differentiate between hominin species, and this made the identification possible. This technique could also be used to identify other fossilized remains of uncertain origins, raising the possibility of finding other archaic human species that might still be hidden somewhere deep in the fossil record.
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A New Technique to Find a Hidden Gem
The Denisovans were closely-related to both modern humans (Homo sapiens) and Neanderthals. They occupied the eastern part of the Eurasian continent during the Pleistocene Epoch, although only a few fossils have been found that prove they existed (most notably at the aptly named Denisovan Cave in the Altai Mountain region of Siberia).
While the search for new Denisovan fossils has picked up steam in recent years, it seems that the existing fossil record may also have something to offer. The jawbone just identified as Denisovan has been lying around for many years, waiting for the technology to advance so it could finally be recognized for what it was.
Map showing location where the Denisovan jawbone was found, plus other Denisovan fossil sites. (Tsutaya, et al./Science).
"The same technique can and is being used to study other hominin fossils to determine whether they too are Denisovans, Neanderthals or other hominin populations," study co-author Frido Welker, a molecular anthropologist at the University of Copenhagen, explained in an interview with Live Science.
The artifact Welker and an international team of experts studied in this case was the Penghu 1 jawbone, a specimen netted by a fisherman trawling the floor of the Penghu Channel, roughly 15.5 miles (25 kilometers) off the west coast of Taiwan. In the decade since Penghu 1 was discovered, paleoanthropologists have argued over which species could properly claim the thick jawbone with the large teeth: Homo sapies had been ruled out, as had the Neanderthals, so the possibilities were Homo erectus, an unknown archaic ancestor, or the Denisovans, who were only first identified in 2010.
Denisovans lived simultaneously with modern humans and Neanderthals, but their fossil footprint is vanishingly small, and they are known mostly from a few DNA samples. This makes it extremely difficult if not impossible to identify Denisovan remains based on anatomical comparisons with existing fossils.
Fortunately, this is not a problem when using a new style of high-tech analysis known as paleoproteomics, which can perform a detailed study of the amino acid and protein sequences found in ancient fossils. It was this method that allowed the scientists to link the jawbone from Taiwan to other Denisovan remains, as scarce as they might be.
The scientists revealed the exciting news of their discovery on April 10 in the journal Science.
"It wasn't possible to make real meaning of this specimen even 8 or 9 years ago," Sheela Athreya, a biological anthropologist at Texas A&M University who was not involved in the study, told Live Science. "This study confirms what we always inferred — that there had been a hominin presence in the farthest extent of eastern Eurasia throughout the Pleistocene."
Denisovan molar, found in Denisovan Cave in Siberia. (Thilo Parg/CC BY-SA 4.0).
But When Did the Denisovan Live?
The researchers are anxious to figure out just how old the Penghu 1 jawbone is, but that will not be so easy. Because the fossil was in the water for so long, traditional dating methods like carbon-14 or uranium dating won’t work, and DNA extraction has also proven impossible.
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Animal bones found near the jawbone suggest one of two possible age ranges: either 10,000 to 70,000 years ago, or 130,000 to 190,000 years ago. If the former is correct, this could be the youngest Denisovan fossil ever found, predating a specimen found on the Tibetan Plateau that has been dated to around 40,000 BC.
But regardless of when he lived (the newly discovered Denisovan has been identified as male), his presence so close to the island of Taiwan shows that the Denisovans ranged far and wide in Asia during their heyday, from the frozen regions of Siberia to the warmer environs of the coastline.
Facial reconstruction of a Denisovan teen girl. (Maayan Harel/Hebrew University of Jerusalem).
"It is now clear that two contrasting hominin groups—small-toothed Neanderthals with tall but gracile mandibles and large-toothed Denisovans with low but robust mandibles—coexisted during the late Middle to early Late Pleistocene of Eurasia," the study authors noted in their Science article.
Now that the researchers have seen what paleoproteomics can do, they are anxious to use it more broadly.
"The meaningful result of this work is that we can do so much more with previously unidentified fossils found in channels and riverbeds in Asia," Athreya said. "That's exciting!"
Top image: The fossilized jawbone found off the west coast of Taiwan, now identified as Denisovan.
Source: Tsutaya, et al./Science.
By Nathan Falde
