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. 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.
Tarsiers have enormous eyes and long feet. Their feet have extremely elongated tarsus bones, which is how they got their name. They are primarily insectivorous, and catch insects by jumping at them. They are also known to prey on birds and snakes. As they jump from tree to tree, tarsiers can catch even birds in motion. Gestation takes about six months, and tarsiers give birth to single offspring. All tarsier species are nocturnal in their habits, but like many nocturnal organisms some individuals may show more or less activity during the daytime. Unlike many nocturnal animals, however, tarsiers lack a light-reflecting area (tapetum lucidum) of the eye. They also have a fovea, atypical for nocturnal animals.