The Truong Son muntjac, or Annamite muntjac, is one of the smallest muntjac species, at about 15 kg, half the size of the Indian muntjac. It was discovered in the Truong Son (Annamite) mountain range in Vietnam in 1997, identified by examination of skulls and descriptions provided by villagers, who call it samsoi cacoong, 'the deer that lives in the deep, thick forest' (Wikipedia, general species account).
It lives at elevations of 400–1,000 m, where its small size allows it to move through dense undergrowth.
Description: Wildlife of Vietnam guide, Wildlife of Everywhere (wildlifeofeverywhere.com); general species information paraphrased from Wikipedia (CC BY-SA)
Mammals of the World