Chevrotains, also called mouse-deer, are small, delicately built mammals with short and thin legs. Although they superficially resemble deer (family Cervidae) due to their brownish coats, which are often striped or spotted, these animals belong to a different family, Tragulidae. Currently, there are 10 extant species of chevrotains, of which only one species, the water chevrotain, is found in Africa, while all others are distributed across South and Southeast Asia.
These even-toed ungulates are primarily herbivorous, feeding on plant parts, though they occasionally consume insects, crabs, or even carrion. Typically solitary, they may occasionally form loose groups or live in pairs.
They are the smallest hoofed mammals (ungulates) in the world, almost the size of a rabbit. The Java mouse-deer (Tragulus javanicus), the smallest living species, averages 18 in (45 cm) in length, 12 in (30 cm) in height, and weighs just 2.2 to 4.4 lb (1 to 2 kg).
In contrast, the largest species, the water chevrotain of Africa (Hyemoschus aquaticus), has a body length of about 2.7 ft (85 cm) and a shoulder height of approximately 1.1 ft (35 cm) and weighs 15 to 35 lb (7 to 16 kg).
Species living in Asia typically weigh between 2 to 9 lb (1 to 4 kg).
These animals have short, compact bodies with slender legs and hairless muzzles. Their coats are reddish-brown on the upper side and white underneath. Members of the genus Moschiola, commonly known as spotted chevrotains, feature pale spots or stripes on their upper bodies, whereas those in the genus Tragulus lack these markings. The water chevrotain, the sole member of the genus Hyemoschus, has a similar reddish-brown topcoat with a white underside.
Their limb structure reflects a mix of primitive and advanced traits. They possess hooved feet and cuboidal carpals while also retaining lateral digits and sometimes walking on their toes (digitigrade). Notably, their hindlimbs are supported by a hard cannon bone, and their forelimb structure varies from one species to another. For example, the third and fourth metacarpals are fused in Asian species but remain separate in African species.
They have a four-chambered stomach for digestion, but the third compartment is poorly developed.
Their skulls lack projections like antlers or horns, though a prominent postorbital bar and a long mandibular condyle are present in all. They, however, lack the sagittal crest commonly found in most mammals.
Like other ruminants, chevrotains lack upper incisors, which are replaced by a horny pad but possess a complete set of lower incisors. They have elongated canines (tusks) that are particularly large and curved in males but smaller in females. These canines extend below their lower lips.
Their dental formula is 0.1.3.3/3.1.3.3 = 34.
The term chevrotain originates from the Middle French word chevrot, meaning fawn, reflecting their close resemblance to baby deer in appearance. Initially, the word chevrotain was used interchangeably for all species found in Asia, namely, members of the genera Moschiola and Tragulus. However, in the most recent taxonomic classification, only members of the genus Moschiola are referred to as chevrotains, while those of the genus Tragulus are called mouse-deer. The African species Hyemoschus aquaticus is universally and consistently referred to as the water chevrotain and not a mouse-deer.
The 10 extant species are grouped under the following 3 genera.
Apart from the 10 extant species, there were 6 extinct genera, namely, Dorcatherium, Dorcabune, Afrotragulus, Siamotragulus, Yunnanotherium, and Archaeotragulus.
This group thrived from the Oligocene Epoch, around 34 million years ago, to the Miocene Epoch, approximately 5 million years ago. They have remained evolutionarily unchanged over this period and continue to represent a living example of an ancient ruminant lineage.
Several species are known only from their fossil records.
All species (except the water chevrotain) are spread across the forests of South and Southeast Asia. The water chevrotain inhabits the rainforests of Central and West Africa, where it primarily lives amidst thick cover on riverbanks.
These animals thrive in the dense undergrowth of forests in their respective regions. They are often found living near water sources for hydration and protection from their enemies.
They are primarily herbivorous, consuming grasses, leaves, buds, and fallen fruits like figs and bananas.
The water chevrotain, however, occasionally consumes insects and crabs. It also scavenges on the residue of fish and other animals.
The average lifespan of these animals ranges from 8 to 12 years. The greater mouse deer, however, can survive up to 16 years in captivity under proper care.
Males possess a prominent intermandibular (chin) gland under their jaw, which they use to rub against females as a way of gauging their receptiveness to mating. If the female is not receptive, she walks away. With their consent, courtship is brief, and mating involves prolonged copulation with no specific breeding season.
After a gestation period of about 4.5 months, the mother gives birth to a single young, which weighs around 370 gm. The young is capable of standing on its feet within 30 minutes of its birth. In about 8 to 12 weeks, the young is weaned, and it reaches sexual maturity at 5 to 10 months of age (depending on the species). Throughout the developmental phase, there is very little parental care.
These mammals are preyed upon by birds of prey, like crested eagle owls, reptiles like crocodiles and pythons, and large cats, such as tigers and clouded leopards.
The Philippine mouse-deer (Tragulus nigricans) is listed as an Endangered (EN) species in the IUCN Red List. The primary causes behind the decline of its numbers include habitat loss, poaching, and trading for its meat and hide.
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