Introduction
Primates constitute an order of the class Mammalia of zoology that includes the lorises, lemurs, monkeys, tarsiers, apes, and humans. The order Primates contains more than 300 species, and it is the third most diverse order of class Mammalia after order Rodentia (rodents) and order Chiroptera (bats). The English name “primates” is derived from French word primat, which is a noun form of the Latin adjective “primat” originating from primus (meaning “prime or first rank”). Carl Linnaeus thought they were the “highest” order of animals, so he named them as ‘Primates’.
About 55-85 million years ago the ancestors of modern primates, known as Plesiadapiformes arose from small mammals (terrestrial). These were adapted for arboreal life in tropical forests. Numerous primate features indicate life adaptations in this demanding environment, which also includes large brains, dexterous hands, clarity of vision, colour vision, and modified shoulder girdle. The smallest of primates is mouse lemur of Madagascar (Microcebus berthae) weighing ~ 35 g and the largest is a gorilla (Gorilla gorilla) weighing more than 140 kg.
Primates differ from other mammals
The brain of primates is bigger compared to other terrestrial mammals in comparison to their body weight. It possesses a unique fissure called the Calcarine sulcus which divides the first and second visual cortexes on either part of the brain.
All terrestrial mammals have hooves or claws on their digits, except primates which possess flat nails. A few primates also have claws, along with flat nail on the big toe. In all primates, other than human, to hold branches, the big toe or hallux separates from the other toes and together forms a pincer. Arboreal mammals have grasping feet indicating that the present-day primates evolved from an arboreal ancestor. All primates are pentadactyl, i.e. have five fingers.
Members of the infra-order Catarrhini (Old World monkeys) which includes monkeys, apes and humans have dexterous hands possessing opposable thumbs. A few of the lemurs and lorises also have an opposable thumb. Primates possess specialized nerve endings known as Meissner’s corpuscles in the feet and hands for tactile sensitivity; no other placental mammal is known to possess this feature. Primates have a big brain (compared to the size of the body) relative to other mammals, they tend to rely on their improved sense of vision, unlike most mammals which rely on the smell-sense. This feature is more advanced in apes and monkeys and remarkably lesser in lemurs and lorises. Also, except for humans and apes, all primates possess tails.
The development in primates is slower in comparison with mammals of similar body size; they reach maturity later and have longer lifespans. Solitary or mated pairs or group lifestyles are all seen in different species of primates. Several species are sexually dimorphic; variations may include fat distribution, muscle mass, size of the canine tooth, pelvic width, hair distribution, along with colouration.
From arboreal mammals, over time have evolved into a terrestrial mode of life, at least partially and several others have evolved a high level of intelligence too. Primates mostly differ due to their behaviour and morphological distinctions among the members of the group is far and few in between. Probably, the most thriving primates are those which have least departed from the ancestral pattern of structure but from the ancestral behavioural pattern, they are the farthest.
Habitat and food habits
The habitats of primates are found almost all over the world. However, primates other than human are restricted in distribution, occurring mostly in Central and South America, Africa and southern Asia. A few species of primates are found in North America as far as southern Mexico and in northern parts of Asia such as Japan. Apart from tropical rainforests primates are seen in savannas, temperate forests, mountains, deserts, and coastal areas.
Most species are primarily adapted for arboreal life but exceptions to this are humans, gorillas and baboons. Locomotion techniques of the arboreals utilized by primates involve leaping from one tree to another and swinging; terrestrial locomotion routines involve bipedalism, i.e. walking or moving on two limbs and altered knuckle-walking.
Primates are omnivorous, they feed on animals such as insects, crustaceans, birds and eggs and other small invertebrates; different parts of plants like fruits, flowers, seeds, nuts, tubers, and rhizomes; and also vegetative parts like grasses, leaves, stems, and also bark and gums.
Classification of Primates
Primates are classified into two suborders:
- Strepsirrhines (wet-nosed), which contains lemurs, galagos, and lorisids
- Haplorhines (dry-nosed), which contains tarsier, monkey, and apes
Threat of Extinction
According to the International Union for Conservation of Nature (IUCN), primate population greater than a third are either vulnerable or critically endangered. Nearly 60% of species of primates are on verge of extinction, which includes: Madagascar species (87%), Asia(73%), Africa(37%), and in South and Central America(36%). In addition, 75% of primate species have declining populations.
Many primate species are critically endangered such as Sumatran Orangutan, Silky Sifaka, the white-headed Langur, Delacour’s Langur, the Tonkin snub-nosed monkey, the Cross River Gorilla, etc.
Deforestation, monkey hunting drives to mitigate crop-raiding, for medicinal use, for food, to be used as pets are the major threats for extinction in most of the areas. Clearing land for agriculture is the foremost cause of forest destruction. Urbanisation and use of timber for various commercial and industrial practices have led to tropical forest destruction. One of the major challenges to primate conservation is the delayed onset of sexual maturity and a prolonged period between births. Hence, recovery from depletion is slow.
Questions and Answers:
1. How many species of primates are known presently and where do they occur? Name the largest and the smallest primate. Which is the most widely distributed primate?
There are about 300 species of primates known worldwide. Primates are found almost all over the world. The habitats of primates are found almost all over the world. However, primates other than human are restricted in distribution, occurring mostly in Central and South America, Africa and southern Asia. A few species of primates are found in North America as far as southern Mexico and in northern parts of Asia such as Japan. Apart from tropical rainforests primates are seen in savannas, temperate forests, mountains, deserts, and coastal areas.
The smallest of primates is mouse lemur of Madagascar (Microcebus berthae) weighing ~ 35 g and the largest is a gorilla (Gorilla gorilla) weighing more than 140 kg. Humans are the most widely distributed primates.
2. List some of the factors responsible for the declining population of primates in the wild.
Deforestation, monkey hunting drives to mitigate crop-raiding, for medicinal use, for food, to be used as pets are the major threats for extinction in most of the areas. Clearing land for agriculture is the foremost cause of forest destruction. Urbanisation and use of timber for various commercial and industrial practices have led to tropical forest destruction. One of the major challenges to primate conservation is the delayed onset of sexual maturity and a prolonged period between births. Hence, recovery from depletion is slow.
3. Name the suborders and infra orders which constitute the Order Primates. Name the groups which are considered as “old world monkeys” and “new world monkeys” and why are they named so?
Primates are classified into two suborders:
- Strepsirrhines (wet-nosed), which contains lemurs, galagos, and lorisids
- Haplorhines (dry-nosed), which contains tarsier, monkey, and apes
Strepsirrhines are further divided into Lemuriformes and Lorisiformes. The infra-orders under haplorhines are Trasiiformes and Simiformes. The parvorders of Simiformes, Platyrrhini and Catarrhini are called New World monkeys and Old World monkeys respectively. The Platyrrhini are found in the Americas which is called the New World and the Catarrhini are found in Africa and Asia which are known as the Old World.
4. List any three characteristics that are unique to primates.
Some unique characteristics of Primates are:
1. The brain of primates is larger than that of other terrestrial mammals in comparison to their body weight. It possesses a unique fissure called the Calcarine sulcus that separates the first and second visual cortexes on either side of the brain.
2. Primates possess flat nails on their digits. A few primates also have claws, along with flat nail on the big toe.
3. Primates possess specialized nerve endings known as Meissner’s corpuscles in the hands and feet for tactile sensitivity.
5. Which is the smallest primate and where is it found?
The smallest primate is mouse lemur (Microcebus berthae) of Madagascar weighing ~35 grams.
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WHAT PRIMATES VS MMAMMALS
Primates belong to an order of mammals. The order Primates is the third most diverse order of mammals and includes more than 500 species. These are distinguished by features such as usage of hands, large brain, and complex behavior. Monkeys, humans, apes, chimpanzees, lemur, gorilla, orangutan, baboon, are all primates. It displays higher levels of cultural adaptability and social interaction.