The treeshrews (or tree shrews) are small mammals native to the tropical forests of Southeast Asia. They make up the familiesTupaiidae and Ptilocercidae and the entire orderScandentia. There are 20 species in 5 genera. Treeshrews have the highest brain to body mass ratio of any animal, even higher than humans. Although called treeshrews, they are not true shrews (although they were previously classified in the Insectivora), and are not all 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[2]:
2.1.3.3
3.1.3.3
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[2]. 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.
Classification
Dentition of Tupaia
Treeshrews were moved from Insectivora to the Primates order, because of certain internal similarities to the latter (for example, similarities in the brainanatomy, highlighted by Sir Wilfred Le Gros Clark), and classified as a primitive prosimian. However, recent molecular phylogenetic studies have strongly suggested that treeshrews should be given the same rank (order) as the primates and, with the primates and the flying lemurs, belong to the clade Euarchonta. According to this classification, the Euarchonta are sister to the Glires (lagomorphs and rodents), and the two groups are combined into the clade Euarchontoglires[3].
However there are other classifications proposed, and the debate about the evolutionary relationships of tree shrews has not yet settled. For example, certain morphological studies[4] suggested that tree shrews are related to bats (or at least to Megachiroptera; see Flying primates theory), together with colugos (Dermoptera), primates and fossil mammals such as Plesiadapiformes. These mammalian orders are traditionally referred to as the Superorder Archonta.
Alternatively, some mammalogists[who?] suggest that Dermoptera are related to Chiroptera (thus forming Volitantia). According to this view tree shrews, not colugos, would be the closest living relatives of primates.
^ Helgen, Kristofer M. (November 16, 2005). in Wilson, D. E., and Reeder, D. M. (eds): Mammal Species of the World, 3rd edition, Johns Hopkins University Press, 104-109. ISBN 0-801-88221-4.
^ ab Martin, Robert D. (1984). in Macdonald, D.: The Encyclopedia of Mammals. New York: Facts on File, 440-445. ISBN 0-87196-871-1.
^ Pettigrew JD, Jamieson BG, Robson SK, Hall LS, McAnally KI, Cooper HM, 1989, Phylogenetic relations between microbats, megabats and primates (Mammalia: Chiroptera and Primates). Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences 325(1229):489-559
