The last sighting of a saola in the wild was in 1998, according to Dang Dinh Nguyen, director of a saola nature reserve in Vietnam's central province of Quang Nam.
In the area where the saola was photographed, WWF has recruited forest guards locally to remove snares and battle illegal hunting, the greatest threat to saolas' survival, the statement said. The snares had been set largely to catch other animals, such as deer and civets, which are a delicacy in Vietnam.
Twenty years since they were first known to science, the elusive mammals remain hard to detect and little is known about them.
At best, no more than few hundred, and maybe only a few dozen, live in the remote, dense forests along Vietnam's border with Laos, WWF said.