Family Tarsiidae
tarsiers

There are 7 extant species of tarsiers, all in the genus Tarsius. Tarsier species are all similar in size, morphology, and ecology. They are all small, nocturnal, predaceous primates specialized for leaping and clinging. Tarsiers are the most "primitive" of the haplorrhine primates, with fossils dating to the Eocene. They were once widely distributed, fossils are known from North America, Europe, North Africa, and Asia. (Niemitz, 2003)

Tarsiers are found only in archipelagos in southeast Asia, including Sumatra, Borneo, Sulawesi, and parts of the Philippine Islands. (Niemitz, 2003)

Tarsier species are all highly arboreal and are found primarily in tropical, forested habitats with dense vertical growth. They use leaping between vertical tree trunks or other vertical supports extensively to get around and this is an important component of their habitats. They may venture into non-forested habitats if there are sufficient vertical surfaces for clinging and leaping. They will jump to the ground to move around as well, but will only remain on the ground momentarily. Sleeping roosts in trees, hollows, and clusters of vines are also important components of their habitats. Most of their foraging time is spent below 1 m in the vertical structure of a forest. Sleeping roosts are mainly at 2 to 5 meters above the ground. (Niemitz, 2003)

Until recently (1984) only 3 extant tarsier species were recognized. Recent research, including molecular systematics, has demonstrated that these 3 species were made up of multiple, cryptic species. It is likely that continued research will result in the recognition of additional species in the near future. Like other haplorrhine primates, tarsiers lack a tapetum lucidum, share a central fovea in the retina, fused frontal bones, and posteriorly closed orbits. They probably evolved from diurnal primate ancestors. Tarsiers were once lumped with the "prosimians" - a group that included lemurs, galagos, and relatives and is now recognized as a separate primate suborder, Strepsirrhini. These were regarded as "primitive" primates. However, there is no validity to a prosimian grouping and that classification is no longer recognized. A second genus of tarsiers, Rabienus, has been proposed but is not currently recognized. (Niemitz, 2003)

Tarsiers are small primates, weighing 80 to 150 g. Their fur is velvety or silky and buff, grayish brown, or dark brown on the back and grayish or buffy on the underside, generally resembling the color of dead leaves or bark. Species from higher altitudes sometimes have curly hair. Their most distinctive features are their round heads, remarkably large eyes that are directed forward, and their medium to large, hairless, and very mobile ears. Their eyes are so large that one of them weighs nearly as much as their brain. Their skin in areas that are naked or with little hair is sometimes colored in areas near skin glands. Males of some species have orange on the skin near their testicles and other species have dark brown spots on their ears, the colors are from gland secretions. Their muzzle is short, and they seem to have almost no neck (although they are capable of turning their head over 180 degrees!). Tarsiers have long, slender bodies, but tend to look round because of their habit of crouching while clinging to a branch. Body lengths are up to 10 cm. Like all haplorrhines, tarsiers have hairs on their nose pads. There is little to no sexual dimorphism, although males may be slightly larger. (Feldhamer et al., 1999; Groves, 1989; Niemitz, 2003; Nowak and Paradiso, 1983; Szalay and Dodson, 1979; Thorington and Anderson, 1984; Vaughan, 1986; Vaughan, Ryan, and Czaplewski, 2000)

Tarsier forelimbs are short and their hindlimbs elongated, the hindlimbs are longer in proportion to body length than in any other mammal. They are unique among mammals in that the elongation of their hindlimbs is the result of lengthening of the tarsals (especially the calcaneum and navicular) rather than the metatarsals. By elongating the tarsals, tarsiers can lengthen the limbs without sacrificing dexterity of the hands, often a result of metatarsal elongation. The elongation of their tarsals gives their names "Tarsiidae" or "Tarsius". The digits are extraordinarily long and tipped with soft, rounded toe pads that help them grip and cling to surfaces. The pollex is not opposable, but the hallux is. All digits have flattened nails except the second and third hind toes, which have claw-like nails used for grooming (sometimes called "toilet claws"). The tail is naked except for tufts of hairs at the tip and is thin and long, from 20 to 25 cm. Philippine tarsiers have scales on their tails. Tarsier species have have ridges of skin on the ventral surfaces of their tail that help them to stabilize themselves against tree trunks when clinging. (Feldhamer et al., 1999; Groves, 1989; Niemitz, 2003; Nowak and Paradiso, 1983; Szalay and Dodson, 1979; Thorington and Anderson, 1984; Vaughan, 1986; Vaughan, Ryan, and Czaplewski, 2000)

The skulls of tarsiers are unmistakeable due to the huge, forward-directed orbits. These have expanded rims and are separated by a thin interorbital septum. The dental formula is 2/1, 1/1, 3/3, 3/3 = 34. The upper medial incisors are large and pointed; the upper canines are small; and the upper molars are tritubercular. (Feldhamer et al., 1999; Groves, 1989; Nowak and Paradiso, 1983; Szalay and Dodson, 1979; Thorington and Anderson, 1984; Vaughan, 1986; Vaughan, Ryan, and Czaplewski, 2000)

Tarsiers can live up to 16 years, although there is little data on wild lifespan for most species. (de Magalhães, 2009)

All tarsier species are nocturnal or crepuscular. Most species live in small social groups, sometimes of just a single male and female but often consisting of a single, dominant male, several females, and their dependent young. Western tarsiers (Tarsius bancanus) seem to be more solitary. Tarsiers are mainly seen alone during their active, nocturnal phase, but often sleep with other individuals during the day, although some species rest alone as well. Social groups and individuals defend territories with scent marking and vocalizations. Scent marks can be quite consistent in some species, indicating very stable home ranges. Males generally have larger home ranges that overlap with those of several females. When social groups get together, they may spend time grooming each other. (Niemitz, 2003; Nowak and Paradiso, 1983; Vaughan, Ryan, and Czaplewski, 2000)

Tarsiers are extremely specialized for vertical clinging and leaping. Their rigid tails with ventral ridges help them to cling to vertical supports. Their extremely elongated hindlimbs, well-developed leg muscles (thigh muscles may represent 12% of total body mass), and long fingers with gripping tips enable them to make impressive leaps of up to 45 times their body length. They are especially adept at backward leaping, propelling themselves backwards, rotating in the air, and landing with their feet. They also use quadrupedal locomotion, small hops, and can run on their hindlimbs on the ground. (Niemitz, 2003; Nowak and Paradiso, 1983; Vaughan, Ryan, and Czaplewski, 2000)

Tarsiers use scent marking and vocalizations to mark and defend territories and to confirm group membership. Scent marking is through urine and gland secretions deposited onto objects in their environment. Glands are on their lips, chest, and anogenital region. Individuals may vocalize, often at dawn and dusk, but duetting or chorusing is also common among members of social groups. Vocalizations at dawn and dusk may represent times when individuals are departing from or arriving at communal resting areas. The majority of their nocturnal foraging time may be spent alone. Some species are relatively silent except for inter-individual contact calls. (Niemitz, 2003; Nowak and Paradiso, 1983; Vaughan, Ryan, and Czaplewski, 2000)

Tarsier species eat only animal prey. They use their exceptional vision and hearing at night to detect prey and their agile, rapid leaps to grab prey up to their own size. Their primary prey are arthropods, especially moths and butterflies, orthopterans, ants, and beetles, but they also eat birds, lizards, and snakes. In most species, foraging occurs most at less than 1.5 meters from the ground. In Tarsius tarsier the majority of prey are caught on branches or leaves (~60%) or in the air (~25%). Only about 5% of prey are caught on the ground. (Niemitz, 2003; Vaughan, Ryan, and Czaplewski, 2000)

Tarsiers may fall prey to any number of arboreal, nocturnal predators that share their tropical, forested habitats. They have been observed mobbing and being captured by snakes and a slow loris (Nycticebus). Their nocturnal habits, exceptionally keen vision and hearing, and their agility protect them from predation to some extent. Their habit of clinging to vertical surfaces makes it more difficult for most animals to capture them. (Niemitz, 2003)

Tarsier species are important predators of arthropod prey and other animals in their tropical forest habitats. They show remarkable convergences with owls and effectively occupy a similar niche. Over 30 convergences have been noted between owls and tarsiers, including external morphology, characteristics of their inner ears, and their ecology. They are host to a diverse fauna of endoparasites. (Niemitz, 2003)

There are no adverse effects of tarsiers on humans.

Tarsiers are generally too small to be hunted for food. They are fascinating primates, providing perspectives on the evolution of their unique locomotion style and life histories. Their nocturnal habits make them difficult to observe, so ecotourism opportunities are limited. However, tarsiers are efficient predators of large arthropods, many of which are crop pests, so help to control their populations. (Niemitz, 2003)

The IUCN recognizes 8 species of tarsiers, including the newly named Lariang tarsier (Tarsius lariang, 2006). Two species are considered endangered, three are considered vulnerable, 1 is near threatened, and 2 are data deficient. All tarsier species are considered threatened by habitat destruction of 30% or more throughout their range and continued taxonomic uncertainty makes assessing risks difficult. In appropriate, primary forest habitat tarsier species can be common, but they become more rare in degraded habitat. They may be negatively impacted by human use of insecticides in some areas. (IUCN, 2009; Niemitz, 2003)