Chevrotains, or mouse-deer, are small even-toed ungulates that make up the family Tragulidae, the only extant members of the infraorder Tragulina. The 10 extant species are placed in three genera, but several species also are known only from fossils. The extant species are found in forests in South and Southeast Asia, with a single species, the water chevrotain, in the rainforests of Central and West Africa. They are solitary or live in pairs, and feed almost exclusively on plant material. Chevrotains are the smallest hoofed mammals in the world. The Asian species weigh between 0.7 and 8.0 kg (1+1⁄2 and 17+3⁄4 lb), while the African chevrotain is considerably larger at 7–16 kg (15–35 lb). With an average length of 45 cm (18 in) and an average height of 30 cm (12 in), the Java mouse-deer is the smallest extant (living) ungulate or hoofed mammal, as well as the smallest extant even-toed ungulate.
H. Milne-Edwards, 1864
In November 2019, conservation scientists announced that they had photographed silver-backed chevrotains (Tragulus versicolor) in a Vietnamese forest for the first time since the last confirmed sightings in 1990.
The word "chevrotain" comes from the French word chevrot (kid or fawn), derived from the Middle French chèvre (goat).
The single African species is consistently known as "chevrotain". The names "chevrotain" and "mouse-deer" have been used interchangeably among the Asian species, though recent authorities typically have preferred chevrotain for the species in the genus Moschiola and mouse-deer for the species in the genus Tragulus. Consequently, all species with pale-spotted or -striped upper parts are known as "chevrotain" and without are known as "mouse-deer".
The Telugu name for the Indian spotted chevrotain is jarini pandi, which literally means "a deer and a pig". In Kannada, it is called barka (ಬರ್ಕ), in Malayalam, it is called കൂരമാൻ kūramān, and the Konkani name for it is barinka. The Tamil term is சருகு மான் sarukumāṉ "leaf-pile deer". The Sinhala name meeminna roughly translates to "mouse-like deer". This was used in the scientific name of the Sri Lankan spotted chevrotain, M. meminna.
The family was widespread and successful from the Oligocene (34 million years ago) through the Miocene (about 5 million years ago), but has remained almost unchanged over that time and remains as an example of primitive ruminant form. They have four-chambered stomachs to ferment tough plant foods, but the third chamber is poorly developed. Though most species feed exclusively on plant material, the water chevrotain occasionally takes insects and crabs or scavenges meat and fish. Like other ruminants, they lack upper incisors. They give birth to only a single young.
In other respects, however, they have primitive features, closer to nonruminants such as pigs. All species in the family lack antlers and horns, but both sexes have elongated canine teeth. These are especially prominent in males, where they project out on either side of the lower jaw, and are used in fights. Their legs are short and thin, which leave them lacking in agility, but also helps to maintain a smaller profile to aid in running through the dense foliage of their environments. Other pig-like features include the presence of four toes on each foot, the absence of facial scent glands, premolars with sharp crowns, and the form of their sexual behaviour and copulation.
They are solitary or live in pairs. The young are weaned at three months of age, and reach sexual maturity between 5 and 10 months, depending on species. Parental care is relatively limited. Although they lack the types of scent glands found in most other ruminants, they do possess a chin gland for marking each other as mates or antagonists, and, in the case of the water chevrotain, anal and preputial glands for marking territory. Their territories are relatively small, on the order of 13–24 hectares (32–59 acres), but neighbors generally ignore each other, rather than compete aggressively.
Some of the species show a remarkable affinity with water, often remaining submerged for prolonged periods to evade predators or other unwelcome intrusions. This has also lent support to the idea that whales evolved from water-loving creatures that looked like small deer.
Traditionally, only four extant species were recognized in the family Tragulidae. In 2004, T. nigricans and T. versicolor were split from T. napu, and T. kanchil and T. williamsoni were split from T. javanicus. In 2005, M. indica and M. kathygre were split from M. meminna. With these changes, the 10 extant species are:
- Family Tragulidae
- Genus Hyemoschus
- Water chevrotain, Hyemoschus aquaticus
- Genus Moschiola
- Genus Tragulus
- Genus Hyemoschus
The Hypertragulidae were closely related to the Tragulidae.
The six extinct chevrotain genera include:
- Genus Dorcatherium
- Genus Dorcabune
- Genus Afrotragulus Sánchez, Quiralte, Morales and Pickford, 2010 
- Genus Siamotragulus
- Genus Yunnanotherium
- Genus Archaeotragulus
- Changing taxonomy in the genus Tragulus make exact species identification uncertain, but either T. javanicus or T. kanchil. Note also the contradicting English and scientific names on the sign on the photo.
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