See M. Kavanagh, Monkeys, Apes and Other Primates (1983); J. R. Napier and P. H. Napier, The Natural History of the Primates (1985).
Any of three species (genus Tarsius, family Tarsiidae) of nocturnal prosimian primates found on several South Asian islands. Tarsiers have large, goggling eyes and a round head that can be rotated 180°. The ears are large, membranous, and almost constantly in motion. Tarsiers are 4–6 in. (9–16 cm) long; the thin, tufted tail of about twice that length provides balance and support. The gray to dark brown fur is thick and silky. Tarsiers cling vertically to trees and leap from trunk to trunk. They have greatly elongated hind limbs and disklike adhesive pads on the digit tips. Tarsiers prey mainly on insects. The well-furred newborn is born with eyes open.
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Tarsiers are prosimian primates of the genus Tarsius, a monotypic genus in the family Tarsiidae, which is itself the lone extant family within the infraorder Tarsiiformes. Although the group was once more widespread, all the species living today are found in the islands of Southeast Asia.
The Tarsier brain is different from other primates in terms of the arrangement of the connections between the two eyes and the lateral geniculate nucleus, which is the main region of the thalamus that receives visual information. The sequence of cellular layers receiving information from the ipsilateral (same side of the head) and contralateral (opposite side of the head) eyes in the lateral geniculate nucleus distinguishes tarsiers from lemurs, lorises, and monkeys, which are all similar in this respect . Some neuroscientists suggested that "this apparent difference distinguishes tarsiers from all other primates, reinforcing the view that they arose in an early, independent line of primate evolution" .
Gestation takes about six months, and tarsiers give birth to single offspring. Young tarsiers are born furred, and with open eyes, and are able to climb within a day of birth. They reach sexual maturity after one year. Adults live in pairs, with a home range of around one hectare.
The phylogenetic position of extant tarsiers within the order Primates has been debated for much of the past century, and tarsiers have alternately been classified with strepsirrhine primates in the suborder Prosimii, or as the sister group to the simians (=Anthropoidea) in the infraorder Haplorrhini. Analysis of SINE insertions, a type of macromutation to the DNA, is argued to offer very persuasive evidence for the monophyly of Haplorrhini, where other lines of evidence, such as DNA sequence data, had remained ambiguous. Thus, some systematists argue that the debate is conclusively settled in favor of a monophyletic Haplorrhini.
At a lower level, it has been indicated that the tarsiers, currently all placed in the genus Tarsius, actually should be placed in two (a Sulawesi and a Philippine-Western group) or three separate genera (a Sulawesi, Philippine and Western group). Species level taxonomy is complex, with morphology often being of limited use compared to vocalizations. Several "vocal morphs" may represent undescribed taxa (such as North Sulawesi "T. tarsier", and a tarsier from the Togian Islands), as may also be the case for a number of poorly known isolated populations (such as the Basilan, Leyte and Dinagat populations of the T. syrichta group, and tarsiers on Siau Island that tentatively have been assigned to T. sangirensis). Further confusion exists over the validity of certain names. Among others, the widely used T. dianae has been shown to be a junior synonym of T. dentatus, and comparably T. spectrum is now considered a junior synonym of T. tarsier. On the contrary T. tarsier has been considered a junior synonym of T. syrichta, but features of the holotype indicate this is incorrect.
Tarsiers have never formed successful breeding colonies in captivity, and when caged, tarsiers have been known to injure and even kill themselves because of the stress.