Primitive primates are typically known as prosimians and consist of lemurs, lorises, pottos, galagoes, and tarsiers. Many refer to this group as lower primates because they are most similar to the earliest primates, which lived tens of millions of years ago. Technically, this group belongs to two suborders: the Strepsirhini (wet nose) and Haplorhini (dry nose). Within Strepsirhini is the infra-order Lemuriformes, which is composed of several superfamilies: Lemuroidea, Indrioidea, and Lorisoidea. At one time, tarsiers were classified as Strep-sirhini, but recent studies in genetics and bio-chemics suggest that tarsiers are more closely related to monkeys and apes than they are to other prosimians. However, if you compare their bony anatomy with that of other primates, they appear to fall within the range of normal variation among the prosimian group. Since they are morphologically more similar to other prosimians, we have chosen to discuss tarsiers in this group of lower primates. Phylogenetically, tarsiers fall under the hyporder (Tarsiiformes), further divided into the suborder of Haplorhines. This suborder has several superfamilies within it, only one of which pertains to the living group of tarsiers (Tarsioidea).
Compared with higher primates (tarsiers, monkeys, apes, and humans), prosimians have a greater reliance on their sense of smell (olfaction). Their longer, foxlike, wet nose reflects this adaptation. In addition, their eyes are located more laterally on the face, and their vision is not stereoscopic as it is in monkeys, apes, and humans. Most have large, mobile ears and eye sockets with a ring of bone (the postorbital bar) rather than the enclosed eye sockets that characterize the higher primates, which are more visually oriented. Most lemurs have long, fuzzy tails (the Indri excepted). They use this tail for balance when leaping from tree to tree, and unlike many New World monkeys, their tails are not prehensile.
Lemurs are found only on the island of Madagascar, located off the southeast coast of Africa, and on the neighboring Comoros Islands. There are twenty-two living species of lemurs, but, at one time, many more species existed in Madagascar and elsewhere. The others became extinct after humans began to inhabit the island region. Living lemurs range in size from the tiny pygmy mouse lemur, which weighs 30 grams (1 oz), to the Indri and the Sifaka, which weigh well over 7 kg (15 lb). They can be found in a wide range of habitats,
from the lush, wet, rain forest in eastern Madagascar to the dry desert in the southwest. With the exception of the ringtail lemur, lemurs spend most of their time in the trees. The ringtail is the most terrestrial of all the lemur species, spending as much as half of its day on the ground. The smaller lemur species tend to be nocturnal, while most of the larger species are diurnal. Lemurs feed primarily on leaves and fruits, although some nocturnal lemurs feed primarily on inscets.
Lorises are found in Southeast Asia and the islands of Malaysia. They live in forested and woodland regions, and most lorises are slow-moving arboreal (tree-dwelling) quadrupeds. Some lorises maintain a grooming claw on their second metatarsal (foot bone). Lorises are nocturnal creatures that live semisolitary lives, but within small groups.
Their diet consists mainly of insects. Their slow and deliberate quadrupedal walk is a convenient weapon when used as a stealth tactic for sneaking up on insects.
Pottos are the African version of the Asian lorises. Nocturnal creatures of habit, they are generally found in a closed canopy environment. Unlike their Asian kin, pottos eat mostly fruit, leaving a very small percentage of their diet to animal protein (insects, ants, termites). Like the Asian lorises, the pottos also have a specialized hand in which the thumb is rotated 180 degrees in divergence from the other digits. This specialization allows them powerful grasping capabilities. In addition to the thumb specialization, the index finger has been reduced to a nub. Pottos have one unique specialization not found in any other primate: their lower cervical vertebra and first thoracic vertebral spinous processes are elongated, giving the potto a great degree of protection of the vertebral column and blood supply from predators.
Galagoes are found in the forests and woodland savannas of the Sahara Desert in Africa. Also nocturnal, galagoes in forested regions occupy the lower levels of the canopy. Galago alleni eats mainly on the ground. Its diet consists mainly of fruit and gums, but it will eat up to 25 percent animal protein when available. The true bushbaby, G. senegtalensis, eats mainly insects and gums off the ground. The locomotion of galagoes is by means of vertical clinging and leaping. Their social groups consist of small groups of neighboring galagoes. Some sleep in leaf nests, others in holes in trees.
Tarsiers are found in the forested regions of Indonesia. Although they look and act like other prosimians, biochemical studies indicate that they are probably more closely related to monkeys. They are small, nocturnal creatures with large, mobile ears, but they lack the wet nose that characterizes prosimians. They may be very similar to the ancestors of the first anthropoids (the taxonomic group that includes monkeys, apes, and humans). Tarsiers have the unique ability to rotate their heads 180 degrees.
As is the case for most mammals, the kind of social group that a prosimian belongs to depends on several factors: whether they are nocturnal or diurnal, whether they are small-or large-bodied, and where they live. Most nocturnal species are solitary (for example, the potto). Diurnal species with large bodies live in larger social groups (for example, the ringtailed lemur). Many wild populations of lemurs and other prosimians are under the threat of extinction. This is primarily because of extensive habitat loss and human hunting. Since humans reached Madagascar, about 2,000 years ago, the once extensive forests have been reduced by more than 90 percent. Many of the other lower primates—lorises, galagoes, and tarsiers—also face the threat of extinction as humans continue to alter and destroy their natural habitats.
—Ken Mowbray and Shara Bailey
See also: Great Apes; Monkeys; Primates Bibliography
Conroy, Glen. 1990. Primate Evolution. New York: W. W. Norton; Fleagle, John. 1988. Primate Adaptation and Evolution. New York: Academic; Schwartz, Jeffrey, Ian Tattersall, and Niles Eldredge. 1978. "Phy-logeny and the Classification of the Primates Revisited." Yearbook of Physical Anthropology 21:95-133; Tattersall, Ian. 1982. Lemurs of Madagascar. New York: Columbia University Press.
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