(Genus Tarsius) Any of three species of small primates, family Tarsiidae, intermediate in form between lemurs and monkeys. Tarsiers are found on several Southeast Asian islands including  the Philippines, Celebes, Borneo, and Sumatra. They have long legs, short bodies, and rounded  heads that can be rotated through 180º. Their faces are short, and the eyes, their most striking  feature, are large and goggling. The ears are large, membranous, and almost constantly in  motion. Tarsiers are about 9-16 cm (3.5-6 inches) long, excluding the tail, which is about twice  that length. Their fur is thick, silky, and coloured gray to dark brown.

Tarsiers cling vertically to trees and leap from trunk to trunk. They are well adapted to an  arboreal life by the great elongation of their hindlimbs, by the expansion of the tips of the digits  into disklike, adhesive pads, and by possession of the long, thin, tufted tail that serves as a  balancer and prop. They are nocturnal animals and prey mainly on insects. A single young is  produced in a fairly well-developed state, well furred and with eyes open; gestation may  require about six months.

The Tarsier was one of the first animals to grace the cover of an O'Reilly book. Since then, these unique engraving-style drawings have become a trademark part of O'Reilly's book design.