The saola was discovered in May 1992 during a joint survey carried out by the Ministry of Forestry of Vietnam and WWF in north-central Vietnam.
The team found a skull with unusual long, straight horns in a hunter's home and knew it was something extraordinary.
The find proved to be the first large mammal new to science in more than 50 years and one of the most spectacular zoological discoveries of the 20th century.
Why are they endangered?
Saola are often caught in snares set in the forest for wild boar, sambar or muntjac deer. Local villagers set some snares for subsistence use and crop protection.
Recent increases in lowland people hunting to supply the illegal trade in wildlife has led to a massive increase in hunting, driven by traditional medicine demand in China and restaurant and food markets in Vietnam and Laos.