The mammal -- often referred to as the "Asian unicorn" even though the antelope-like creature has two horns -- is so rare that only 250 are believed to exist worldwide, and none are in captivity.
The BBC reports that the saola -- discovered in Southeast Asia in the early 1990s -- has never been seen in the wild by biologists. Its existence, to date, has been confirmed only in photos by local villagers.
"The death of this saola is unfortunate," said a Bolikhamxay province conservation spokesman. "But at least it confirms an area where it still occurs, and the government will immediately move to strengthen conservation efforts there."
Pierre Comizzoli, a member of the International Union for Conservation of Nature, said that "a lack of knowledge of saola biology is a major constraint to efforts to conserve it."
He also indicated that the saola may not have a lot of time left for future study.
"At best, a few hundred survive, but it may be only a few dozen," he said. "The situation is critical."
Read more at the BBC and Cryptomundo.