A primate is a member of the biological order Primates (Latin: "prime, first rank), the group that contains lemurs, the Aye-aye, lorids, galagos, tarsiers, monkeys, and apes, with the last category including humans. With the exception of humans, which now inhabit every continent on Earth, most primates live in tropical or subtropical regions of the Americas, Africa and Asia. Primates range in size from the 30 g (1 ounce) Pygmy Mouse Lemur to the 200 kg (440 pound) Gorilla. According to fossil evidence, the primitive ancestors of primates may have existed in the late Cretaceous period around 65 mya (million years ago), and the oldest known primate is the Late Paleocene Plesiadapis, c 55–58 mya. Molecular clock studies suggest that the primate branch is even older, originating in the mid-Cretaceous period around 85 mya.
The Primates order is informally divided into three main groupings: prosimians, monkeys of the New World, and monkeys and apes of the Old World. The bodies of the prosimians most closely resemble those of the early proto-primates. The best-known of the prosimians, the lemurs, are located on the island of Madagascar and to a lesser extent on the Comoros Islands, isolated from the rest of the world. The New World monkeys, which include the familiar capuchin, howler, and squirrel monkeys, live exclusively in the Americas. With the exception of humans, the Old World monkeys and the rest of the apes inhabit Africa and southern and central Asia, although fossil evidence shows many species existed in Europe as well.
Primates are adapted for a tree-dwelling lifestyle. Anatomical adaptations support their reliance on vision, their dominant sensory system, rather than smell, the dominant sensory system in most mammals. Three-color vision has developed in some primates. Most primates also have opposable thumbs and some have prehensile tails. Many species are sexually dimorphic, in that males and females have different physical traits, including body mass, canine tooth size, and coloration. Primates have slower rates of development than other similarly sized mammals, and reach maturity later but have longer lifespans. Locomotion techniques used include, leaping from tree to tree, walking on two or four limbs, knuckle-walking and swinging between branches of trees (known as brachiation). Some species live in solitude, others are monogamous, and others live in groups of up to hundreds of members.
}} }} }} The Primates order lies in a tight clustering of related orders (the Euarchontoglires) within the Eutheria, a subclass of Mammalia. Recent molecular genetic research on primates, colugos, and treeshrews has shown that the two species of colugos are more closely related to the primates than the treeshrews, even though the treeshrews were at one time considered primates. These three orders make up the Euarchonta clade. This clade combines with the Glires clade (made up of the Rodentia and Lagomorpha) to form the Euarchontoglires clade. Variously, both Euarchonta and Euarchontoglires are ranked as superorders. Also, some scientists consider Dermoptera a suborder of Primates and call the "true" primates the suborder Euprimates.
The Aye-aye is difficult to place in Strepsirrhini. Theories have been proposed that its family, Daubentoniidae, is either be a lemuriform primate (meaning its ancestors split from lemur line more recently than the lemurs and lorises split) or that it is sister to all of the other strepsirrhines. Research confirms that the Aye-aye family, Daubentoniidae, is a lemuriform.
The suborder Haplorrhini, the "dry-nosed" primates, is composed of two sister clades. The prosimian tarsiers in family Tarsiidae (monotypic in its own infraorder Tarsiiformes), represent the most primitive division at about 58 mya. The Simiiformes infraorder emerged about 40 mya, and contains the two clades: the parvorder Platyrrhini that developed in South America and contains New World monkeys is one, and the parvorder Catarrhini that developed in Africa and contains the Old World monkeys, humans and the other apes in the other. A third clade, which included the eosimiids, developed in Asia but went extinct millions of years ago.
Apes and monkeys spread from Africa into Europe and Asia. Close behind came lorises and tarsiers, also African castaways. The first hominid fossils were discovered in Northern Africa and date back 5–8 mya. Molecular and fossil studies generally show that modern humans originate in Africa 100–200 Ka (thousand years ago).
A few new species are discovered each year, and the evaluation of current populations as distinct species is in flux. Biological anthropologist Colin Groves listed about 350 species of primates in Primate Taxonomy in 2001. The recently published third edition of Mammal Species of the World (MSW3) lists 376 species. But even the latter list falls short of current understanding as its collection cutoff was in 2003, and a number of publications since then have pushed up to 406 species. Notable new species not listed in MSW3 include the Bemaraha Woolly Lemur (Avahi cleesei, named after British actor and lemur enthusiast John Cleese) and the GoldenPalace.com Monkey (whose name was put up for auction).
The order Primates was established by Carl Linnaeus in 1758, in the tenth edition of his book Systema Naturae, for the genera Homo (humans), Simia (other apes and monkeys), Lemur (prosimians) and Vespertilio (bats). In the first edition of the same book (1735), he had used the name Anthropomorpha for Homo, Simia and Bradypus (sloths). In 1839, Henri Marie Ducrotay de Blainville, following Linnaeus and imitating his nomenclature, established the orders Secundates (including the suborders Chiroptera, Insectivora and Carnivora), Tertiates (or Glires) and Quaternates (including Gravigrada, Pachydermata and Ruminantia), but these new taxa were not accepted.
In older classifications, the Primates were divided into two superfamilies: Prosimii and Anthropoidea. The Prosimii included all of the prosimians: all of Strepsirrhini plus the tarsiers. The Anthropoidea contained all of the simians.
The primate skull has a large domed cranium which is particularly prominent in anthropoids. The cranium protects the large brain, a distinguishing characteristic of this group. The endocranial volume (the volume within the skull) is three-fold greater in humans than in the greatest non-human primate, reflecting a larger brain size. The mean human endocranial volume is 1201 cubic centimetres, it is 469 cm³ in gorillas, 400 cm³ in chimpanzees and 397 cm³ in orangutans. The primary evolutionary trend of primates has been the elaboration of the brain, in particular the neocortex (a part of the cerebral cortex) which is involved with sensory perception, generation of motor commands, spatial reasoning, conscious thought and, in humans, language. While other mammals rely heavily on their sense of smell, the arboreal life of primates has led to a tactile, visually dominant sensory system, a reduction in the olfactory region of the brain and increasingly complex social behavior.
Primates generally have five digits on each limb (pentadactyly), with keratin nails on the end of each finger. The bottom sides of the hands and feet have sensitive pads on the fingertips. Most have opposable thumbs, a characteristic primate feature; however opposing thumbs are not limited to this order (opossums, for example, also have them). Thumbs allow some species to use tools. In primates, the combination of opposing thumbs, short fingernails (rather than claws) and long, inward-closing fingers is a relic of the ancestral practice of gripping branches, and has, in part, allowed some species to develop brachiation (swinging by the arms from tree limb to tree limb) as a significant means of transportation. Prosimians have clawlike nails on the second toes of their feet.
The primate collar bone is retained as prominent element of the pectoral girdle; this allows the shoulder joint broad mobility. Apes have more mobile shoulder joints and arms due to the dorsal position of the scapula, broad ribcages that are flatter front-to-back, and a shorter, less mobile spine compared to Old World monkeys (with lower vertebrae greatly reduced, resulting in tail loss in some species). Old World monkeys are unlike apes in that most have tails, and unlike the New World monkeys in that their tails are never prehensile. Only the New World Atelidae family have prehensile tails.
Primates show a trend towards a reduced snout. Technically, the distinction of Old World monkeys from New World monkeys depends on the structure of the nose, and the distinction of Old World monkeys from apes depends on the arrangement of their teeth. In New World monkeys the nostrils face sideways; in Old World monkeys, they face downwards. There is a considerably varied dental pattern in primates and although some have lost most of their incisors, all retain at least one lower incisor. In most strepsirhines, the lower incisors form a toothcomb which is thought to be used in grooming and possibly foraging. Old World monkeys also have eight premolars, compared with twelve in New World monkeys. The Old World species are divided into apes and monkeys depending on the number of cusps on their molars; apes have five, Old World monkeys have four. The main hominid molar cusp (hypocone) evolved in early primate history, while the cusp of the corresponding primitive lower molar (paraconid) was lost. Prosimians are distinguished by their immobilized upper lips, moist tip to their nose and forward-facing lower front teeth.
The evolution of color vision in primates is unique among most eutherian mammals. While the remote vertebrate ancestors of the primates possessed three color vision (trichromacy), the nocturnal, warm-blooded, mammalian ancestors lost one of three cones in the retina at the time of dinosaurs. Fish, reptiles and birds are therefore trichromatic while all mammals, with the exception of some primates and marsupials, are strictly dichromats. Catarrhines are routinely trichromatic, platyrrhines, on the other hand, are trichromatic in a few cases only.
Howler monkeys have reinvented routine trichromatism through a recent gene duplication of the red-green opsin gene. Howler monkeys are one of the most specialized leaf-eaters of the New World monkeys, fruits are not a major part of their diet, and the type of leaves they prefer to consume (young, nutritive, and digestible), are detectable only by a red-green signal. Field work exploring the dietary preferences of howler monkeys suggests that routine trichromacy was environmentally selected for.
Comparative analyses have substantiated the sexual selection hypotheses, and have generated a more complete understanding of the relationship between sexual selection, natural selection, and mating systems in primates. Studies are helping to find the relative contribution of the various selective and non-selective mechanisms in sexual dimorphism evolution and expression. These studies have shown that dimorphism is the product of changes in both male and female traits. Ontogenic scaling, where relative extension of a common growth trajectory occurs, may give some insight into the relationship between sexual dimorphism and growth patterns. Some evidence from the fossil record suggests that there was convergent evolution of dimorphism, and some extinct hominids probably exceeded dimorphism of any living primate.
Various species of primates move by brachiation, bipedalism, leaping, arboreal and terrestrial quadrupedalism, climbing or knuckle-walking. Several prosimians are primarily vertical clinger and leapers. These include many bushbabies, all indriids (i.e., sifakas, avahis and indris), sportive lemurs, and all tarsiers. Other prosimians are arboreal quadrupeds and climbers. Some are also terrestrial quadrupeds, while some are leapers. Most monkeys are both arboreal and terrestrial quadrupeds and climbers. Gibbons, muriquis and spider monkeys all use brachiation extensively. Woolly monkeys also sometimes brachiate. Orangutans use a similar form of locomotion called quadramanous climbing, in which they use their arms and legs to carry their heavy bodies through the trees. Chimpanzees and gorillas knuckle walk, and can move bipedally for short distances. Humans are the only fully bipedal species.
Other systems are known to occur as well. For example, with howler monkeys both the males and females typically transfer from their natal group upon reaching sexual maturity, resulting in groups in which neither the males or females are typically related. Some prosimians, colobine monkeys and callitrichid monkeys also use this system.
Primatologist Dr. Jane Goodall, who studied in the Gombe Stream National Park, noted fission-fusion societies in chimpanzees. There is fission where the main group splits up to forage during the day, then fusion when the group returns at night to sleep as a group. This social structure can also be observed in the Hamadryas Baboon, spider monkeys and the Bonobo. The Gelada has a similar social structure in which many smaller groups come together to form temporary herds of up to 600 monkeys.
These social systems are affected by three main ecological factors: distribution of resources, group size and predation. Within a social group there is a balance between cooperation and competition. Cooperation comes in the form of allogrooming; whereby ectoparasites are removed and wounds cleaned, food sharing and collective defense against predators or of a territory. Competition is demonstrated by aggression and may come about through availability of food, sleeping sites or mates. Aggression is often used in establishing social hierarchies.
The Red-tailed Monkey associates with several species, including the Western Red Colobus, the Blue Monkey, Wolf's Mona Monkey, the Mantled Guereza, the Black Crested Mangabey and Allen's Swamp Monkey. Several of these species are also predated on by the Common Chimpanzee.
In South America, but not in Central America, squirrel monkeys associate with capuchin monkeys. This may have more to do with foraging benefits to the squirrel monkeys rather than anti-predation benefits.
Primates have a longer juvenile period between weaning and sexual maturity than other mammals of similar size. During the juvenile period, primates are more susceptible than adults to predation and starvation; they gain experience in feeding and avoiding predators during this period. They also learn social and fighting skills, often through playing.
In addition to reaching maturity later, primates have longer lifespans than other similarly sized mammals. Lifespans are generally longer for female primates than males.
Primates exploit a variety of food sources. Most primates include fruit in their diets to obtain easily digested carbohydrates and lipids for energy. However, they require other foods, such as leaves or insects, for amino acids, vitamins and minerals. Many primates have anatomical specializations enabling them to exploit particular foods, such as fruit, leaves, gum or insects. For example, leaf eaters such as howler monkeys, black-and-white colobuses and sportive lemurs, have extended digestive tracts to enable them to absorb nutrients from leaves that can be difficult to digest. Marmosets, which are gum eaters, have strong incisor teeth, enabling them to open tree bark to get to the gum, and claws rather than nails, enabling them to cling to trees while feeding. Some species have additional specializations. For example, the Grey-cheeked Mangabey has thick enamel on its teeth, enabling it to open hard fruits and seeds that other monkeys cannot.
The Gelada is the only primate species that feeds primarily on grass. Tarsiers are the most carnivorous primates, exclusively eating insects, reptiles, amphibians and other live animals. Capuchin monkeys, on the other hand, can exploit many different types of food, including fruit, leaves, flowers, buds, nectar, seeds, insects and other invertebrates, and small vertebrates such as birds, bird eggs, lizards, squirrels and bats. The Common Chimpanzee has a varied diet that includes predation on other primate species, such as the Western Red Colobus monkey.
Primates evolved from arboreal animals, and many species live most of their lives in trees. Some species are partially terrestrial, such as baboons and the Patas Monkey and a few species are fully terrestrial, such as the Gelada and Humans. Non-human primates live in a diverse number of forested habitats in the tropical latitudes of Africa, India, Southeast Asia, and South America, including rainforests, mangrove forests, and montane forests. There are some examples of non-human primates that live outside of the tropics; the mountain-dwelling Japanese Macaque lives in the north of Honshu where there is snow-cover eight months of the year; the Barbary Macaque lives in the Atlas Mountains of Algeria and Morocco. Primates also have a considerable vertical range; the Black Snub-nosed Monkey has been found living in the Hengduan Mountains at altitudes of 4,700 meters (15,400 ft), the Mountain Gorilla can be found at 4,200 metres (13,200 ft) crossing the Virunga Mountains and the Gelada has been found at elevations of up to 5,000 meters (16,400 ft) in the Ethiopian Highlands. Although most species are generally shy of water, a few are good swimmers and are comfortable in swamps and watery areas, including the Proboscis Monkey, De Brazza's Monkey and Allen's Swamp Monkey, which has developed small webbing between its fingers. Some primates, such as the Rhesus Macaque and gray langurs, can exploit human-modified environments and even live in cities.
Many species of primates have varied relationships with humans. Some are kept as pets, others used as model organisms in laboratories or in space missions. They also serve as service animals for the disabled. Capuchin monkeys can be trained to assist quadraplegics. Their intelligence, memory and manual dexterity allows them to perform tasks that a quadraplegic is physically unable to do.
Primates can act as vectors for spreading viruses such as Herpesviridae, Poxviridae, measles, ebola, rabies, the Marburg virus and viral hepatitis. Some of these are zoonotic diseases that can also be transmitted to humans, most notably, the potentially fatal Herpes B Virus. They may be killed in monkey drives to protect agriculture. Human activities have often been detrimental to primates, and have threatened numerous primate species with extinction.
The International Union for Conservation of Nature (IUCN) lists more than a third of its primates as critically endangered, endangered or vulnerable. Common threats to primate species include deforestation, forest fragmentation, primate crop raiding, and primate hunting for use in medicines, as pets, and for food. Large-scale tropical forest clearance is widely regarded as the process that most threatens primates. More than 90% of primate species occur in tropical forests. The main cause of forest loss is clearance for agriculture, although commercial logging, subsistence harvesting of timber, mining, and dam construction also contribute to tropical forest depletion. In Indonesia large areas of lowland forest have been cleared to increase palm oil production, and one analysis of satellite imagery concluded that during 1998 and 1999 there was a loss of 1,000 Sumatran Orangutans per year in the Leuser Ecosystem alone.
Primates with a large body size (over 5 kg) have an increased extinction risk due to their increased profitability to poachers compared to smaller primates. They also have a slow life history with an increased sexual maturity age and a longer period between births. Populations therefore have a slower recovery time after the loss of members to poaching or the pet trade. In some African cities estimates suggest that half of all protein consumed in urban areas comes from the bushmeat trade. Endangered primates such as guenons and the Drill are hunted at levels that far exceed sustainable levels. This is due to their large body size, ease of transport and profitability per animal. As farming encroaches on forest habitats, primates feed on the crops, causing the farmers large economic losses. Primate crop raiding gives locals a negative impression of primates, hindering conservation efforts.
Madagascar, home to five endemic primate families, has experienced the greatest extinction of the recent past; since human settlement 1,500 years ago, at least eight classes and fifteen species have become extinct due to hunting and habitat destruction. Among the primates wiped out were Archaeoindris (a lemur larger than a silverback gorilla) and the families Palaeopropithecidae and Archaeolemuridae.
In Asia, Hinduism, Buddhism, and Islam prohibit eating primate meat; however primates are still hunted for food. Some smaller traditional religions allow the consumption of primate meat. The pet trade and traditional medicine also increase demand for illegal hunting. The expanding Chinese middle class has also increased demand for exotic pets in recent years. The Rhesus Macaque, a model organism, was protected after overtrapping threatened its numbers in the 1960s; the program was so effective that the macaques are now seen as a pest throughout their range.
In Central and South America forest fragmentation and hunting are the two main problems for primates. Large tracts of forest are now rare in Central America. This increases the amount of forest vulnerable to edge effects such as farmland encroachment, lower levels of humidity and a change in plant life. Movement restriction results in a greater amount of inbreeding, which can cause deleterious effects leading to a population bottleneck, whereby 50% of the population is lost.
In the United States the main threat is the pet trade. Although primate import for the pet trade was banned in 1975, smuggling still occurs along the United States–Mexico border. Prices range from $3000 for monkeys to $30,000 for apes.
There are 21 critically endangered primates, 8 of these species have remained on the IUCN's "The World's 25 Most Endangered Primates" list since the year 2000: the Silky Sifaka, Delacour's Langur, the White-headed Langur, the Gray-shanked Douc, the Tonkin Snub-nosed Langur, the Hainan Black Crested Gibbon, the Cross River Gorilla and the Sumatran Orangutan. Miss Waldron's Red Colobus was recently declared extinct when a report from 1993–1999 could find no trace of the subspecies. However, hunters have killed individuals since then but its prospects remain bleak.
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