The saola, also called spindlehorn, Asian unicorn, or infrequently, Vu Quang bovid, is one of the world's rarest large mammals, a forest-dwelling bovine native to the Annamite Range in Vietnam and Laos. It was described in 1993 following a discovery of remains in Vũ Quang National Park by a joint survey of the Vietnamese Ministry of Forestry and the World Wide Fund for Nature. Saolas have since been kept in captivity multiple times, although only for short periods as they died within a matter of weeks to months. The species was first reported in 1992 by Do Tuoc, a forest ecologist, and his associates. The first photograph of a living saola was taken in captivity in 1993. The most recent one was taken in 2013 by a movement-triggered camera in the forest of central Vietnam. It is the only species in the genus Pseudoryx.

Bovines comprise a diverse group of 10 genera of medium to large-sized ungulates, including cattle, bison, African buffalo, water buffalos, and the four-horned and spiral-horned antelopes. The evolutionary relationship between the members of the group is still debated, and their classification into loose tribes rather than formal subgroups reflects this uncertainty. General characteristics include cloven hooves and usually at least one of the sexes of a species having true horns. The largest extant bovine is the gaur.