For decades, fishermen sailing off the coast of Taiwan have sometimes discovered fossils in their trawling nets: the bones of elephants, buffalo and other big mammals that lived tens of thousands of years ago, when the sea level was so low that Taiwan was linked to Asia by a land bridge.

But in 2010, a Taiwanese paleontologist was presented with a particularly odd find: a fossil that looked like half a gorilla’s jaw. Scientists have puzzled over it ever since.

Now the mystery of the underwater jaw has been solved. On Wednesday, a team of researchers announced that it belonged to a Denisovan, a member of a mysterious lineage of humans related to Neanderthals. The discovery significantly expands the range of firmly identified Denisovan fossils, previously known from Siberia and Tibet.

“Indeed, Denisovans were present all the way east to the coast,” said Frido Welker, a molecular anthropologist and an author of the new study.

Chun-Hsiang Chang, a paleontologist at Taiwan’s National Museum of Natural Science, first learned of the jaw in 2010 from a private collector. Inspecting it, he could tell right away that it did not belong to a gorilla. Gorillas and other apes have U-shaped jaws. Instead, the fossil jaw angled outward from the chin, as our jaws do.

But the jaw lacked the prominent chin found in today’s humans. “At that time, I thought it looked like a human, but not a modern human,” Dr. Chang said. “I thought it was very important, so I pushed the private collector to lend it to my museum.”