The treeshrews (or tree shrews) are small mammals native to the tropical forests of Southeast Asia. They make up the families Tupaiidae, the treeshrews, and Ptilocercidae, the pen-tailed treeshrews, and the entire order Scandentia. There are 20 species in 5 genera. Treeshrews have a higher brain to body mass ratio than humans, though this is not uncommon for animals weighing less than a kilogram.
Although called treeshrews, they are not true shrews (although they were previously classified in the Insectivora), and not all species are necessarily arboreal. Among other things, they eat Rafflesia fruit. They have no clear fossil record.
Treeshrews are slender animals with long tails and soft, greyish to reddish-brown fur. The terrestrial species tend to be larger than the arboreal forms, and to have larger claws, which they use for digging up insect prey. They are omnivorous, feeding on insects, small vertebrates, fruit, and seeds. They have poorly developed canine teeth and unspecialised molars, with an overall dental formula of: 
Treeshrews have good vision, which is binocular in the case of the more arboreal species. Most are diurnal, although the Pen-tailed Treeshrew is nocturnal.
Female treeshrews give birth to up to three young after a gestation period of 45–50 days, in nests lined with dry leaves inside tree hollows. The young are born blind and hairless, but are able to leave the nest after about a month. During this period, the mother provides relatively little maternal care, visiting her young only for a few minutes every other day to suckle them. Treeshrews reach sexual maturity after around four months, and breed for much of the year, with no clear breeding season in most species.
These animals live in small family groups, which defend their territory from intruders. They mark their territories using various scent glands, or urine, depending on the particular species.
The name Tupaia is derived from tupai the Malay word for squirrel and was provided by Sir Stamford Raffles.
In 2008, researchers found that the Pen-tailed Treeshrew in Malaysia was able to consume large amounts of naturally fermented nectar of up to 3.8% alcohol content the entire year without having any effects on behaviour. Investigation to how these animals cope with that diet is still ongoing. (see msnbc news article)
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