Although the group was prehistorically more globally widespread, all of the species living today are restricted to Maritime Southeast Asia, predominantly in Brunei, Indonesia, Malaysia and the Philippines.

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.

[14] Tarsiers are small animals with enormous eyes; each eyeball is approximately 16 millimetres (0.63 in) in diameter and is as large as, or in some cases larger than, its entire brain.

[16][17] The unique cranial anatomy of the tarsier results from the need to balance their large eyes and heavy head so they are able to wait silently for nutritious prey.

[18] Tarsiers also have long hind limbs, owing mostly to the elongated tarsus bones of the feet, from which the animals get their name.

The combination of their elongated tarsi and fused tibiofibulae makes them morphologically specialized for vertical clinging and leaping.

[21] Their dental formula is also unique: 2.1.3.31.1.3.3[22] Unlike many nocturnal vertebrates, tarsiers lack a light-reflecting layer (tapetum lucidum) of the retina and have a fovea.

The tarsier's brain is different from that of 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.

[34] Tarsiers tend to be extremely shy animals and are sensitive to bright lights, loud noises, and physical contact.

[37][21][38] Tarsiers are the only entirely carnivorous extant primates, albeit mainly insectivorous, catching invertebrates by jumping at them.

[39][40][41] However, it has been found that their favorite prey are arthropods, beetles, arachnids, cockroaches, grasshoppers, katydids, cicadas, and walking sticks.

Tarsiers have never formed successful breeding colonies in captivity; this may be due in part to their special feeding requirements.

[43][44][45][46][47] A sanctuary near the town of Corella, on the Philippine island of Bohol, has had some success restoring tarsier populations.

Tarsiers are a conservation-dependent species, meaning that they need to have more and improved management of protected habitats, or they will become extinct in the future.

From December 2014 to January 2016, female and male T. syrichta were observed based on their time apportioned to normal activities during non-mating versus mating seasons.

During the non-mating season, a significant amount of their waking hours was spent scanning prior to resting, foraging, and traveling.