Like elephant shrews, tree shrews have often been considered a divergent family of Insectivora. They differ from members of that family, however, in possessing complete auditory bullae and zygomatic arches. Their orbits are large, and behind the orbit is a well-developed and complete postorbital process. Some investigators have suggested that they might also be related to Primates. Here, we follow Anderson and Jones (1984) and place them in their own Order, Scandentia. The order contains one family (Tupaiidae) containing 5 genera and around 19 living species.
Tree shrews are remarkably squirrel-like in external shape and size, and in fact I have seen them in pet stores being sold as Asian squirrels. Even the tail of most species is squirrel-like, long and heavily furred. They lack the long vibrissae of squirrels, however, and their forefeet are also rather different, having a full complement of 5 functional toes rather than 4, as in squirrels.
The dental formula of tupaiids is 2/3, 1/1, 3/3, 3/3 = 38. Their upper incisors tend to be canine-like, but the upper canines are molar-like. The molars are broad and resemble many Insectivora in having a dilambodont cusp pattern.
Tree shrews are omnivorous. Their eyes are large and their hearing is excellent. They are often active during the day. They may be found in trees or on the ground. Socially, some species are solitary, others are found in pairs or even small groups. Tree shrews are found in deciduous forests of central and southeastern Asia, but they do not occur on New Guinea or in Australia.
<<<<<<<>>>>>>>ARTIODACTYLA CARNIVORA CETACEA CHIROPTERA DASYUROMORPHIA DERMOPTERA DIDELPHIMORPHI DIPROTODONTIA HYRACOIDEA INSECTIVORA LAGOMORPHA MACROSCELIDEA MICROBIOTHERIA MONOTREMATA NOTORYCTEMORPHIA PAUCITUBERCULATA PERAMELEMORPHIA PERISSODACTYLA PHOLIDOTA PRIMATES PROBOSCIDEA RODENTIA SCANDENTIA SIRENIA TUBULIDENTATA XENARTHRA