Ancient human history is now resurfacing, quite literally, from the bottom of the sea. Off the western coast of Taiwan, dredged from the murky sediment of a long-submerged land bridge, scientists have found a fossil jawbone. It’s not just any fossil, but one that reshapes the map of human ancestry.

The jawbone belonged to a male Denisovan, confirmed by ancient proteins locked in bone for tens of thousands of years. Until now, the Denisovans — an enigmatic branch of archaic humans — had only been identified with certainty in Siberia and Tibet. This new discovery shows that they also extended to East Asia, and maybe even further.

Denisovan proteins

Denisovans are like our ghostly, long-lost relatives. They were first identified in 2010 from DNA extracted from a pinkie bone in Denisova Cave, Siberia. Since then, researchers have found that many people have traces of Denisovan DNA, but hard evidence of their presence — bones, teeth, faces — has been scarce.

This is where the new fossil comes in.

The jawbone was discovered by fishers trawling in the Penghu Channel off Taiwan, a stretch of seafloor that once connected Taiwan to the Chinese mainland. The channel is known for yielding numerous fossils dredged up from bottom sediments.

The fossil was recovered sometime before 2008 but there was some controversy around it. It was difficult to date, and it was unclear whether this belonged to a Denisovan or some other human. It showed unusual anatomical features — such as its robust shape and large teeth — that resembled the Denisovan jaw found in Xiahe, Tibet, but without hard data, a confirmation was not possible.

Extracting DNA had also proven challenging. But by turning to palaeoproteomics — analyzing ancient proteins preserved in tooth enamel and bone — the researchers cracked the case.

They extracted 4,241 amino acid residues from the fossil and zeroed in on five specific protein variants. Two of them, in the proteins ameloblastin (AMBN) and collagen alpha-2(I) chain (COL1A2), were previously found only in Denisovans.

Impressive adaptability

The Denisovan lineage is no longer an outlier tucked in the Siberian cold. It is a branching, adapting, thriving group that crossed mountain ranges and migrated to distant tropical shores.

Denisova Cave lies in Siberia’s icy Altai Mountains. Xiahe, where we found another Denisovan jaw, sits 3,280 meters above sea level on the Tibetan Plateau. In contrast, Penghu is at just 23°N, in a far warmer and more humid climate. This variability demonstrates remarkable adaptability, the study authors say.

“These are climate and environmental conditions that are quite different,” said Enrico Cappellini, of the University of Copenhagen, a co-senior author on the paper. “The cold environment in Siberia, high altitude in Tibet. We cannot infer anything of their cognitive abilities … but they had an ability to adapt to environments that are quite diverse.”

This also suggests at a greater variety of hominins roaming around, and quite possibly, interbreeding.

“The identification of Penghu 1 as a Denisovan mandible confirms the inference from modern human genomic studies that Denisovans were widely distributed in eastern Asia,” the researchers write in their paper.

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 (as a population or as a male character) — coexisted during the late Middle to early Late Pleistocene of Eurasia.

Still, the story remains incomplete. No Denisovan skull has ever been found. The few bones we have form a fragmentary puzzle. But each new piece draws the outline clearer. And now, thanks to a mandible from the bottom of the Taiwan Strait, we know that the Denisovans once stood here too, looking out over a land that is now lost to the waves.

The study was published in the journal Science.