A group of mammals belonging to the order Scandentia, and included in a single family, the Tupaiidae. They are endemic to the Indomalayan region, with a geographic range that extends from India to the Philippines. They reach their greatest diversity on the Southeast Asian island of Borneo, where ten of the twenty known species occur. Five genera of treeshrews are commonly recognized: Tupaia, Anathana, Dendrogale, Urogale, and Ptilocercus,of which Tupaia is the most diverse and best known.
Treeshrews are relatively small, squirrel-like mammals ranging in average body weight from less than 50g to about 300g. In many respects they retain anatomical features closely resembling the primitive eutherian mammalian condition. They have long, tapering muzzles with a moist glandular nosepad; relatively large eyes; small rounded hairless ears; a long slender body, covered in soft dense fur, which is
brown to olive in color, often with streaks or stripes; they have five short digits on their hands and feet, each bearing a well-developed claw; and a long, usually bushy tail, which is as at least as long as the head and body in most species.
They primarily inhabit lowland and montane forest, but do occur in secondary forest, plantations, and gardens. Some species are predominantly arboreal, although they often descend to the forest floor, where they forage for invertebrates and small fruits. Other species are largely or exclusively terrestrial. All of the species are diurnal (i.e., active during the day), except for the nocturnal pen-tailed treeshrew (belonging to the genus Ptilocercus). They are active, agile, and fast-moving creatures who are skilled climbers and leapers in trees and dense undergrowth. Treeshrews are generally territorial, with a paired male and female defending a small home range. Adults build nests in trees, hollow logs, or underground burrows as sleeping sites. During the breeding season, females produce two offspring, who are born hairless and with their eyes closed. They have a remarkable “absentee” maternal care system in which the mother gives birth to her young in a separate nest from her own and only visits them every other day for a few minutes to nurse them.
Since their initial discovery in the late18th century, their taxonomic position has proved problematic. Historically, they have been of interest to anthropologists because of their anatomical similarities and close relationship to primates, and they have sometimes been included in the same order. They share several key specializations with primates, including enlarged forward-facing eyes enclosed by a complete bony ring, a reduction in the sense of smell, a specialized tooth-comb at the front of the lower jaw (as in lemurs and lorises), a relatively large brain, postcranial adaptations for arboreal climbing, ridged skin on the palms and soles, and a small litter size. However, current authorities, while still acknowledging a close evolutionary link with primates, prefer to include them in their own order, but group them together with primates, bats, and flying lemurs or colugos in the superorder Archonta.
The fossil record for treeshrews is poorly known, and the earliest undoubted representatives come from the later Miocene (about 10 million years ago) of Indo-Pakistan and China.
References:
- Corbet, G. B., & Hill, J. E. (1992). The mammals of the Indomalayan region: A systematic review. Oxford: Oxford University Press.
- Emmons, L. H. (2000). Tupai: A field study of Bornean treeshrews. Berkeley: University of California Press.
- Martin, R. D. (1990). Primate origins and evolution: A phylogenetic reconstruction. Princeton, NJ: Princeton University Press.
