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Feb. 21, 2012

Chevrotains and the World of Unusual, Tiny Ungulates

by Kara Rogers

Click to enlarge images

In the dense undergrowth of the tropical forests of Southeast Asia lives the world’s smallest hoofed mammal, the lesser Malay chevrotain (Tragulus kanchil). Weighing around 2 kg (4.4 pounds) and measuring about 50 cm (1.6 feet) in length, the little arched-back creature teeters along on delicate, stilt-like legs, dwarfed by the oversized jungle vegetation.

Lesser Mouse Deer (Tragulus javanicus) Photo credit: Linda Kenney

The lesser Malay is one of 10 living species of chevrotains, which are also known as mouse deer, because of their small size and deer-like appearance. And similar to deer, chevrotains have two-toed hooves and specialized stomachs that allow them to regurgitate and chew on partially digested plant matter to help breakdown undigestible cellulose -- characteristics that classify them as ruminants. Chevrotains, however, are the most primitive ruminants alive today, as evidenced by their lack of horns or antlers, their long upper canine teeth, and their three-chambered stomachs (as opposed to the typical four-chambered anatomy of other ruminants). These features, along with certain pig-like characteristics, have led some scientists to conclude that chevrotains form an evolutionary link between ruminants and nonruminants, or animals with single-chambered stomachs, such as pigs and humans.

But while information about the physical traits of chevrotains is available, knowledge of their behavior is lacking, in large part because of their secretive nature. For example, it was long thought that the lesser Malay chevrotain was nocturnal, but a radiotracking study published in 2003 that was conducted at the Kabili-Sepilok Forest Reserve on the island of Borneo described daytime foraging and nighttime resting, suggesting that the species is not nocturnal. That same study also revealed that lesser chevrotains in the reserve tended to spend early and late daylight hours in areas where gaps in the forest canopy permitted dense growth of climbing bamboo (Dinochloa), which presumably offered cover from predators when foraging for fruit and leaves. With the onset of darkness, the animals moved to elevated ridge areas to rest.

The lesser Malay chevrotain is one of six species in the genus Tragulus. Several of these species are readily distinguished by their size, geographical range, or coat coloration; others, however, are so similar in appearance that scientists can tell them apart only through careful analysis of cranial features. Such analyses have led to the division of the six species into 24 subspecies.

Tragulus Javanicus (Lesser Malay Mouse-deer) in the Jerusalem Zoo

Other chevrotains include the Indian, yellow-striped, and white-spotted chevrotains of the genus Moschiola and the water chevrotain of the genus Hyemoschus. The Indian chevrotain typically is found on rocky, grassy hillsides or near streams in tropical deciduous and evergreen forests throughout much of India. The yellow-striped and white-spotted chevrotains, on the other hand, are found only in Sri Lanka, with the former inhabiting the wet, southwestern region and the latter the dry region that characterizes the east, west, and north of the country. All members of Moschiola are thought to be nocturnal and feed on shrubs, herbs, and fruit.

The water chevrotain (Hyemoschus aquaticus) is perhaps the best characterized and most unusual of the group, known for its tendency to dive underwater to escape predators. However, with its round, rodent-like body, spindly legs, and hoofed feet, it is an inefficient swimmer and tires quickly as it paddles along. Compared with other chevrotains, the water chevrotain is large, weighing 7 to 16 kg (15 to 35 pounds) and standing about 30 to 40 cm (1 to 1.3 feet) at the shoulder. It’s reddish-brown coat has dull white streaks and spots, which may help it to blend in with the dense cover of the tropical forests that characterize its native habitat in western and central Africa.

At least four species of chevrotains, including the water chevrotain, the silver-back chevrotain (T. versicolor), Williamson’s chevrotain (T. williamsoni), and the larger Malay chevrotain (T. napu), are decreasing in number. In addition, the Balabac chevrotain (T. nigricans), which inhabits the tiny island of the same name in the far southwestern Philippines, is endangered. However, because there is insufficient data on the actual population status of these species, and because national and local laws have not been enforced in the Philippines, little has been done to protect these amazing animals.
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Kara Rogers is a freelance science writer and senior editor of biomedical sciences at Encyclopaedia Britannica, Inc. She is a member of the National Association of Science Writers and author of Science Up Front on the Britannica Blog. She holds a Ph.D. in Pharmacology/Toxicology, but enjoys reading and writing about all things science. You can follow her on Twitter at @karaerogers.

About Kara Rogers

Kara is a freelance science writer and senior editor of biomedical sciences at Encyclopaedia Britannica, Inc. She is the author of Out of Nature: Why Drugs From Plants Matter to the Future of Humanity (University of Arizona Press, 2012).

The views expressed are those of the author and are not necessarily those of Science Friday.

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