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Treeshrew

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Treeshrew

Treeshrews[1]
Temporal range: ?Middle Eocene – Recent
Madras Treeshrew (Anathana ellioti)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Eutheria
Superorder: Euarchontoglires
Order: Scandentia
Wagner, 1855
Families

The treeshrews (or tree shrews or banxrings[2]) 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 five genera. Treeshrews have a higher brain to body mass ratio than any other mammals, including humans,[3] however, high ratios are not uncommon for animals weighing less than a kilogram.

Though called treeshrews, they are not true shrews – even though they were previously classified in the Insectivora – and not all species live in trees. Among other things, treeshrews eat Rafflesia fruit.

Among orders of mammals, treeshrews are closely related to primates, and have been used as an alternative to primates in experimental studies of myopia, psychosocial stress and hepatitis.[4]

Characteristics

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: 2.1.3.33.1.3.3[5]

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 have a gestation period of 45 to 50 days and give birth to up to three young 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.[5]

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,[6] and was provided by Sir Stamford Raffles.[7]

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. An investigation as to how these animals cope with this diet is still ongoing.[8]

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 brain anatomy, 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 (colugos), 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.[9] Other arrangements of these orders were proposed in the past.[10]

Euarchontoglires
Glires

Rodentia (rodents)


Lagomorpha (rabbits, hares, pikas)


Euarchonta

Scandentia (treeshrews)



Dermoptera (Colugos)



Plesiadapiformes


Primates





Fossil record

The fossil record of treeshrews is poor. The oldest putative treeshrew, Eodendrogale parva, is from the Middle Eocene of Henan, China, but the identity of this animal is uncertain. Other fossils have come from the Miocene of Thailand, Pakistan, India, and Yunnan, China, as well as the Pliocene of India. Most belong to the family Tupaiidae, but some still-undescribed fossils from Yunnan are thought to be closer to the pen-tailed treeshrew (Ptilocercus). Named fossil species include Prodendrogale yunnanica, Prodendrogale engesseri, and Tupaia storchi from Yunnan, Tupaia miocenica from Thailand, and Palaeotupaia sivalicus from India.[11]

References

  1. ^ Helgen, K. M. (2005). Wilson, D. E.; Reeder, D. M, eds. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. pp. 104–109.  
  2. ^  
  3. ^ "Tupaia belangeri". The Genome Institute, Washington University. Retrieved January 2012. 
  4. ^ Cao, J; Yang, E-B; J-J; Li, Y; Chow P (2003). "The tree shrews: adjuncts and alternatives to primates as models for biomedical research". J Med Primatol 32: 123–130. Retrieved January 2012. 
  5. ^ a b Martin, Robert D. (1984). Macdonald, D., ed. The Encyclopedia of Mammals. New York: Facts on File. pp. 440–445.  
  6. ^ Nowak, R. M. (1999). Walker's Mammals of the World. Johns Hopkins University. p. 245.  
  7. ^ Craig, John (1849). A new universal etymological technological, and pronouncing dictionary of the English Language. 
  8. ^ msnbc news article
  9. ^ Janecka, Jan E.; Miller, Webb; Pringle, Thomas H.; Wiens, Frank; Zitzmann, Annette; Helgen, Kristofer M.; Springer, Mark S.; Murphy, William J. (2007-11-02). "Molecular and Genomic Data Identify The Closest Living Relatives of Primates". Science 318 (5851): 792–4.  
  10. ^ 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 B 325 (1229): 489–559.  
  11. ^ Ni, X.; Qiu, Z. (2012). "Tupaiine tree shrews (Scandentia, Mammalia) from the Yuanmou Lufengpithecus locality of Yunnan, China". Swiss Journal of Palaeontology 131: 51–60.  
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