Suborder Prosimii (strepsirrhines)

Taxonomy    Anatomy, Physiology and Behavior

Prosimian Taxonomy

Almost all the prosimians occur naturally only in Madagascar. The exception are the lorises and galagos, found in sub-Saharan Africa, India, Southeast Asia and the East Indies.{4048} Taxonomy according to the ACLAM blue book{2765} is as follows:

Suborder Prosimii (strepsirrhines)

    a. Superfamily Lemuroidea

        I. Family Lemuridae (lemurs)

        II. Family Indriidae (sifakas, indris)

    b. Superfamily Lorisoidea

    c. Superfamily Daubentonioidea (aye-ayes)

    d. Superfamily Tarsioidea (ACLAM slide series calls this a suborder, and Walker's Primates of the World {4048}calls it a family in the suborder Haplorhini). 

But according to Nowak{4048}, the taxonomy goes like this:

Suborder Strepsirhini

a. Family Lemuridae (ring-tailed, gentle, brown, black, crowned, red-bellied, mongoose and ruffed lemurs)

b. Family Indriidae (indri, avahi, and sifakas)

c. Family Lorisidae (angwantibos, lorises, pottos, and galagos; all found in Africa and Asia)

d. Family Daubentoniidae (aye-aye)

e. Family Cheirogaleidae (dwarf, mouse and fork-marked lemurs)

f. Family Megaladapidae (sportive and koala lemurs)

Prosimians first evolved in the Northern Hemisphere, in North America and Europe, over 65 million years ago. Living prosimians are found only in the Old World tropics today.

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Prosimian Anatomy, Physiology and Behavior

Most, but not all, prosimians are nocturnal. A typical prosimian skull has proportionally large orbits, a reduced braincase, elongated snout, and more highly-developed auditory and olfactory regions than the anthropoid apes. In addition, the living Strepsirhini all have a tooth comb (prominent lower incisors), a grooming claw (second digit on the foot), a postorbital bar instead of a closed orbit, a well-developed moist rhinarium, and a tapetum lucidum in the eye. These anatomic features are characteristic of nocturnal animals. Nocturnal adaptations include large eyes, sensitive night vision provided by the tapetum lucidum, large independently movable ears, elaborate tactile hairs and a well-developed sense of smell. Their systems of communication and social relationships also differ from diurnal animals.{4048}

Family Cheirogaleidae: Microcebus murinus, the mouse lemur, at left.  The family Cheirogaleidae includes nine small, nocturnal species. Although prosimians do not hibernate, one species of dwarf lemur, Cheirogaleus, stores up fat in its tail and hind legs. During the winter they undergo periods of torpor. Cheirogaleids are typically arboreal, spending their days sleeping in nests or tree holes. They move quadrupedally.{4048}

  Lemur catta with its distinctive striped tail, and Varecia variegata (ruffed lemur) on the right.

Family Lemuridae: True lemurs (Lemur, Eulemur, Varecia, and Hapalemur) are diurnal and medium in size. Varecia is quadrupedal.{4048}

Family Indriidae: The indris (Indri) and sifakas (Propithecus), both diurnal, are the largest of the living lemurs. They have greatly elongated legs to help them with leaping and vertical clinging.{4048}

Family Daubentoniidae: The aye-aye (Daubentonia madagascariensis) is the single member of the family Daubentoniidae. It is arboreal and nocturnal, sleeping in tree nests during the day and foraging at night. It is usually described as being "bizarre" due to some anatomic features that relate to its diet and feeding habits. Unlike all the other primates, its incisors grow continuously. It also has a skeleton-like middle finger, used for feeding. Finally, its "huge batlike ears" help it listen for beetle larvae beneath tree bark.{4048} Daubentonia is "one of the most bizarre of living prosimians" because of its rounded brain shape, high degree of flexion between the neurocranium and splanchnocranium, rodent-like incisors, lack of orbital impressions on the frontal lobes, and the arcuate suprasylvian sulcus. All these may be explained by the fact that they gnaw through wood and coconut shells to get at insects, aided by their sense of hearing. They remove food from the insides of nuts with their elongated third digits.{3342,4048}

Family Lorisidae: Loris tardigradus (slender loris on the left) and Nycticebus coucang (the slow loris on the right) are both found in India. 

The slender loris has no tail and weighs 85-350 grams, smaller and more slender than the slow loris. Slender lorises are arboreal and nocturnal. They move with a slow, steady climb, always holding on by three limbs. They stalk their prey and make a fast grab for insects and small vertebrates. Most live alone or with a mate, with births occurring twice a year and one or two babies each time. They are hunted in India for alleged medicinal body parts, and are in appendix 2 of CITES.{4048} N. coucang is larger in size (375-2000 grams) and also has a vestigial tail. Note the dark midline stripe on the neck and back, and the light streak between the dark orbital rings.  They are also arboreal and nocturnal. They climb slowly and deliberately, but to catch their prey they will stand on a branch and make a sudden leap to grab their prey in both hands. They eat mollusks, insects, lizards, birds, small mammals and fruit.  Several groups have been kept successfully in captivity. Breeding occurs throughout the year, with a 185-197 day gestation and a single infant. They are also on appendix 2 of CITES.{4048}

Otolemur crassicaudatus (thick-tailed galago), from Africa, at left.

In sub-Saharan Africa are found three other genera of lorises (Pseudopotto, Arctocebus, and Perodicticus) and a dozen species of galagos (Galago, Galagoides, Otolemur). Galagos, or bushbabies, are another subfamily of lorises. They are all small, nocturnal primates. Their ears move back and forth rapidly giving them a quizzical expression. Their digits have flat disks of thickened skin that aid in gripping limbs. The nails are flattened except for a grooming claw on the second digit of the foot. They eat acacia gum and insects which they catch with their hands. In addition to auditory communication, galagos spread urine on their hands and feet to mark where they go. Galagos are in appendix 2 of CITES.{4048}

Otolemur garnettii, Garnett's Greater Bush Baby, is raised in captivity and is used for behavioral and neurobiology research in the US. They breed readily, and their small size and non-herpes-B status make them good comparative subjects for study. They can be easily anesthetized with sevoflurane for collection of blood samples, with minimal changes in clinical chemistries.{4539}

Tarsiers

Tarsiers (Tarsius) are placed either with the Strepsirhines or with the Haplorhines, depending on the taxonomist, because they have some anthropoid traits as well as prosimian traits. They are small and nocturnal, and live in Indonesia, Malaysia, Borneo and the Philippines. Like anthropoids, they lack a tapetum lucidum, having instead a fovea for visual acuity. They also have a dry nose and small olfactory bulbs, indicating that they (along with Aotus) are "secondarily nocturnal". They have huge, fixed eyes, each of which is larger than their brains, in an complete bony socket. Their legs have elongated tarsal bones to aid in leaping, and their fingers and toes are long to help with vertical clinging.{4048}

©1999, Janet Becker Rodgers, DVM, MS, DipACLAM, MRCVS

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Comments? Send an email to janet.rodgers@vet.ox.ac.uk