The saola (Pseudoryx nghetinhensis), 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.

In May 1992, the Ministry of Forestry, Vietnam sent a survey team to examine the biodiversity of the newly established Vu Quang National Park.

The team ascribed these features to a new bovid species, calling it the "saola" or the "Vu Quang ox" to avoid confusion with the sympatric serow.

[8] According to biodiversity specialist Tony Whitten, though Vietnam boasts a variety of flora and fauna, many of which have been recently described, the discovery of as large an animal as the saola was quite unexpected.

The species was first described in 1993 by Vu Van Dung, Do Tuoc, biologists Pham Mong Giao and Nguyen Ngoc Chinh, Peter Arctander of the University of Copenhagen and John MacKinnon.

[2] The discovery of saola remains in 1992 generated huge scientific interest due to the animal's special physical traits.

A recent sequencing study of ribosomal mitochondrial DNA of a large taxon sample divides the bovid family into two major subfamilial clades.

The first clade is the subfamily Bovinae consisting of three tribes: Bovini (cattle and buffaloes, including the saola), Tragelaphini (Strepsicerotini) (African spiral-horned bovids) and Boselaphini (the nilgai and four-horned antelope).

The specific name nghetinhensis refers to the two Vietnamese provinces of Nghệ An and Hà Tĩnh, while Pseudoryx acknowledges the animal's similarities with the Arabian or African oryx.

[15] The general characteristics of the saola, as shown by studies during 1993–5 as well as the 1998 study, include a chocolate brown coat with patches of white on the face, throat and the sides of the neck, a paler shade of brown on the neck and the belly, a black dorsal stripe, and a pair of nearly parallel horns, present on both sexes.

[2][15][16] Robichaud noted that the hair, straight and 1.5–2.5 centimetres (0.59–0.98 in) long, was soft and thin–a feature unusual for an animal that is associated with montane habitats in at least a few parts of its range.

The tail, which measured 23 centimetres (9.1 in) in Robichaud's specimen, is divided into three horizontal bands, brown at the base, black at the tip and white in the middle.

[18] The saola has round pupils with dark-brown irises that appear orange when light is shone into them; a cluster of white whiskers about 2 centimetres (0.79 in) long with a presumably tactile function protrude from the end of the chin.

The glands are covered by a thick, pungent, grayish green, semi-solid secretion beneath which lies a sheath of few flat hairs.

In Vietnam and Laos, the species' range appears to cover approximately 5,000 km2 (1,900 sq mi), including four nature reserves.

[21] Local people reported that the saola is active in the day as well as at night, but prefers resting during the hot midday hours.

Robichaud noted that the captive female was active mainly during the day, but pointed out that the observation could have been influenced by the unfamiliar surroundings the animal found herself in.

Marking behaviour in the female involved opening up the flap of the maxillary gland and leaving a pungent secretion on rocks and vegetation.

[15] Robichaud offered spleenwort (Asplenium), Homalomena, and various species of broad-leaved shrubs or trees of the family Sterculiaceae to the captive animal.

Saola suffer losses through local hunting and the illegal trade in furs, traditional medicines, and for use of the meat in restaurants and food markets.

Because the people in this area are traditional hunters, their attitude about killing the saola is hard to change; this makes conservation difficult.

[29] Researchers have stationed within villages around the Phou Sithon Endangered Species Conservation Area (PST) where saola have been spotted.

Based on interviews that were conducted amongst the villagers, they have stated that poachers enter the restricted areas, illegally hunting the last saola.