linguistic:paraphrasing
Classification

The phylogenetic position of extant tarsiers within the order Primates has been debated for much of the 20th 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 Haplorhini. Analysis of SINE insertions, a type of macromutation to the DNA, is argued to offer very persuasive evidence for the monophyly of Haplorhini, where other lines of evidence, such as DNA sequence data, remain ambiguous. Thus, some systematists argue the debate is conclusively settled in favor of a monophyletic Haplorrhini. In common with simians, tarsiers have a mutation in the L-gulonolactone oxidase (GULO) gene, which prevents their bodies from synthesizing vitamin C so they must find it in the diet. Since the strepsirrhines do not have this mutation and have retained the ability to make vitamin C, the genetic trait that confers the need for it in the diet would tend to place tarsiers with haplorhines.

At a lower phylogenetic level, the tarsiers have, until recently, all been placed in the genus Tarsius, while it was debated whether the species should be placed in two (a Sulawesi and a Philippine -western group) or three separate genera (Sulawesi, Philippine and western groups). Species level taxonomy is complex, with morphology often being of limited use compared to vocalizations. Further confusion existed 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.

In 2010, Colin Groves and Myron Shekelle suggested splitting the genus Tarsius into three genera, the Philippine tarsiers (genus Carlito), the western tarsiers (genus Cephalopachus), and the eastern tarsiers (genus Tarsius). This was based on differences in dentition, eye size, limb and hand length, tail tufts, tail sitting pads, the number of mammae, chromosome count, socioecology, vocalizations, and distribution. The senior taxon of the species, T. tarsier was restricted to the population of a Selayar island, which then required the resurrection of the defunct taxon T. fuscus.

In 2014, scientists published the results of a genetic study from across the range of the Philippine tarsier, revealing previously unrecognised genetic diversity. Three subspecies are recognised in the established taxonomy: Carlito syrichta syrichta from Leyte and Samar, C. syrichta fraterculus from Bohol, and C. syrichta carbonarius from Mindanao. Their analysis of mitochondrial and nuclear DNA sequences suggested that ssp. syrichta and fraterculus may represent a single lineage, whereas ssp. carbonarius may represent two lineages – one occupies the majority of Mindanao while the other is in northeastern Mindanao and the nearby Dinagat Island, which the authors termed the 'Dinagat-Caraga tarsier'. More detailed studies that integrate morphological data will be needed to review the taxonomy of tarsiers in the Philippines.