CLASSIFICATION OF THE ORDER PRIMATE

Transcription

1 CLASSIFICATION OF THE ORDER PRIMATE INTRODUCTION: Primates are a diverse group of animals represented by humans, monkeys, prosimians and apes. They share some common characteristics such as large brain size, keen vision, dexterous hands and a generalized skeleton for great physical agility. They also tend to have smaller litters than other animals, devoting more care and attention to the rearing of their offspring s. The unique combination of traits found in the primates distinguishes them from other animals. Modern contemporary scientific theories and Charles Darwin theory of evolution suggests that millions of years ago some animals developed characteristics to be the precursors of later primates including humans. Darwin posited that humans share a common ancestor (now extinct) with living apes. They evolved along lines completely different from modern gorillas and chimpanzees. HISTORY OF CLASSIFICATION: Aristotle first developed an approach to nature for the classification of living beings in 4 th century B.C. The categories were based upon visible similarities and one member of each category was considered its primate (from the Latin word Primus, meaning the first or best of Group). In response to discoveries around the globe and in the inner working of organisms, Swedish naturalist Carl Linnaeus developed the Systema Naturae a system of nature, in the 18 th century to classify all living things. This compendium reflected a new understanding for the place of man among the animals. Linnaeus noted the similarity among humans, monkeys and apes classifying them together as primates. The basic biological unit of classification is the species. A species is the largest normally interbreeding population. As species name is made up of two words a capitalized generic name and a trivial name. This system of classification is known as Binomial nomenclature. Genera usually include species which are very similar yet differ in body size or some relatively minor feature of body proportions, behaviour, coat colour etc. They are in turn clustered into families. Families are sub-divided into sub-families or clustered into super families. Family group nomina also follow a definite pattern. Family name ends in suffix idae e.g., Hominidae whereas Super families end in - oidea e.g. Hominoidea. Modern taxonomy or the science of classification (from the Greek word for naming divisions) while retaining the structure of the Linnaean system, is based on more than body structure function and growth. Today scientists compare protein structure, Nucleic acids and genomes to establish phylogeny of organisms. EVOLUTION PATTERNS: As Linnaeus and his contemporaries considered species as fixed entities. However naturalists became increasingly aware of continuities between different forms of life. A proponent of this idea was Charles Darwin. His theory of evolution set out in 1859 in The Origin of Species accepted the fact of human evolution. The theory of evolution tells us that we are all living fossils. So, all of us preserve within ourselves the genes of our ancestors. Darwin himself used comparative anatomy to support his

2 views. One of the triumphs of molecular biology has been to uncover thousands of other cues of relatedness hidden in our genes. We share many of these with other primates e.g. humans and chimpanzees have blood groups, protein and great stretches of DNA in common. The new comparative anatomy based on molecules; make it possible to draw accurate phylogenetic trees for humans and our relatives. CHARACTERISTICS OF PRIMATE: Primate evolution has produced some key physical and anatomical traits that represent adaptations to arboreal conditions i.e. life in trees. Among the most important physical characteristics of primates is their generalized skeletal structure which allows for a great deal of flexibility in movement e.g. in primates the clavicle provides both support and flexibility which enable them to rotate their shoulders and arms to perform a range of movements such as ability to reach for branches and food while roaming through treetops in the wild. The same development in man enhances their ability to drive cars, catch baseballs, etc. Dexterity in the digits (fingers and toes) of the feet and hand, another key primate trait makes it easy for primates to grasp and manipulate objects. All primates have sensitive pads on their fingertips rather than claws and many have five digits on their feet and hand which can be used for grasping objects. An important distinguishing element of the primate hand is the opposable thumb found in humans and many other primates which makes them adept at manipulating small objects. The dental structure of primates is consistent with an omnivorous diet made up of a variety of foods such as plants, fruits, nuts and seeds insects and other animals. Refined vision also sets primates apart. Primates have large eyes oriented to the front protected by bony structures rely heavily on vision. This visual orientation favours binocular and stereoscopic vision in which the visual fields of eyes overlap, transmitting images to both sides of the brain. A distinguishing trait of the primates is size and complexity of the brain. Primates have large brains relative to body size compared to other land animals. The brains of marine mammals have comparable brain size. In primates, the neo-cortex, the surface portion of the brain associated with sensory messages and voluntary control of movement features a large number of convolutions or folds which maximize the surface area. As they evolved, these larger brains undoubtedly helped primates to locate food and to avoid predators. In contrast to most other animals, primates produce few offspring and these undergo long period of gestation i.e. the length of time the young spend in the mother s womb. CLASSIFICATION OF PRIMATE : The living primates are divided into two sub-orders. Until recently the sub-divisions have been the lower primates or Prosimii and the higher primates or Anthropoidea. The division is based on relative brain size. Brains sizes of lower primates have similar size to other mammals while higher primates have large brain size relative to body size.

3 PROSIMII: Modern prosimians have changed relatively little from their ancestors and reside in small isolated population. They include lemurs and Aye-ayes of Madagascar (an island off the east coast of Africa), the lorises of Tropical South East Asia and Africa and the tarsiers of South East Asia. A heightened visual sense makes most of the living prosimians nocturnal, although they do not have color vision. All nocturnal prosimians are characterized by the possession of a tapetum cellulosum, an iridescent layer of cells in the choroids coat of the eye, which is responsible for vivid eye shine in the presence of light. However, like their fellow primates they possess stereoscopic vision and enlarged brains relative to other animal. This enables them to co-ordinate leaping and food gathering in their arboreal environment. A keen sense of smell is, helping them to seek out food and shelter at night. Like other primates, the prosimians use the five dexterous digits on their hands and feet to grasp objects for moving easily through trees. All the living prosimians have nails instead of claws on their digits, but some have retained grooming claws on the hind feet to clean their fur. The jaws are generally elongated in a fox-like muzzle, but it is in the possession of the typical rhinarium and crescentic nostrils of less specialized mammals that the lemurs exhibit their truly primitive character which differs from all other primates. The skull have many primitive mammalian features, such as the presence of a large palatine bone in the inner wall of the orbit, the general absence of an external auditory meatus, the complete absence of a postorbital wall-rendering the orbit and the temporal fossae (the region below the temple) confluent; the orbits, though directed somewhat laterally, have eyeballs mounted in them in such a manner that the eyes look forward and not to the side, a distinct advantage upon the condition encountered by the insectivores. The inner ear preserves the lower mammalian character by the presence of an auditory bulla, a large, spherical, inflatened chamber on the base of the skull which lies the tympanic ring, which in the catarrhini assists in forming the external auditory meatus. Lemuroidea: The super family Lemuroidea inhabits Madagascar Isle. Lemurs represent this Super-family. They are arboreal creatures with nocturnal habits. There seems to be an association between sleeping habits or walking activity, size of the eyes, body size and social habits, for the smaller lemurs (e.g. Lepilemur). They have the largest eyes. They live in small social units or in family groups. The larger lemurs (e.g Indri) on the other hand are frequently quite active by day or in twilight. They have small eyes, and more often tend to live as members of a community of their own species. This suggests that increase in body size might have been a

4 deciding factor to abandon their nocturnal or crepuscular habits among the early primates. This enabled them to hold their kind against. This further led to the development of more extended social relations with members of their own species. The diet of lemurs is varied. Normally they are fruigivorous. Many eat both animal and vegetable foods. Daubentonioidea: A unique lemuroid of this super family is the aye-ayes of Madagascar. They are characterized by the presence of large rodent like incisor teeth and gross reduction in the rest. The dental formula is I 1/1, C 0/0, PM 1/0, M 3/3 a total of 18 teeth. Their digits are provided with claws except hallux. Furthermore the hind finger of each hand is thin and elongated which is used to open wood boring grub s tunnels. The middle fingers are used to probe the tunnels spear the occupants. This lemur occupies the ecological niche of wood peckers which are not found in Madagascar. Some authors refer to this animal as the vertical clinging quadruped. Earlier taxonomists classified Daubentonia among the rodents. In fact many anatomical features of these animals depart considerably from other Lemurs. Yet they possess significant characters of the skull, limbs and viscera. Lorisoidea: The Lorisoidea found in Africa and Asia differs from the other Prosimians in several distinctive ways. They are smaller having larger ears and eyes. In addition they are more or less tailless, slow-moving with rudimentary or completely reduced index-finger. The reduced second toe has a long cleaning claw. The super family Lorisoidea comprises various genera. Characteristics features of some genus are given below: The Potto (Perodicticus) is the size of a small cat. It is characterized by a unique specialization. The spines of the last cervical and the first two thoracic vertebrae project through the skin capped by horny spines constitutes a formidable defense weapon against attackers. The Bush Babies (Gagidae) are about the size of a rat characterized by the presence of long bushy tails, short muzzles, large mobile ears and enormously elongated ankle (metatarso- tarsals) bones which make them remarkable jumpers among the primates. The dwarf bush baby (Galagoides), e.g. which nestles easily on the palm of a man s hand can leap a dozen or more feet upward or in any direction. The head can be turned around so that the nose is in line with the vertebral column. The digits of the hands and feet are slender and long. The well developed pollex and hallux are widely opposed to the other digits. The pelvic limbs are much longer than the pectoral limbs. The lorises cannot leap and climb by hand over hand motion. The galagoes progress by rapid saltation. Tarsioidea: The super family Tarsioidea includes only one genus, an animal called tarsius. It is found only in South-East Asia today. Structurally, tarsius falls somewhere between the lemur and

5 anthropoids. Tarsiers differ from lemurs rather they resemble anthropoids by the absence of a wet, dog like snout on their reduced olfactory apparatus. For these reasons they are often classified alongwith simians under the suborder Anthropoidea. Although tarsiers do not have the enlarged brains and fused lower jaws characteristic of living simians which classify them separately (with other prosimians) they resemble simians in many anatomical details. In its embryological development, the fertilized tarsier ovum sinks into the lining of the mother s uterus and becomes surrounded with lakes of maternal blood. It is similar to man, apes and monkeys, but not to lemurs and lorises whose developing embryos are walled off from direct contact with mother s bloodstream. The nose is quite unlike the lemurs, only a narrow strip of naked skin marks the opening of the widely separated nostrils and the upper-lips shows a continuous smooth surface uninterrupted by median groove. The eyes of tarsiers are very much enlarged each eyeball is roughly the size of the brain they display some simian characteristics. Tarsiers are in the size range of hamsters or kittens, arboreal and nocturnal. The limbs are highly specialized, the fore limbs for grasping and the hind ones for the rapid hop which is their mode of locomotion on the ground. The diet of tarsiers appears to be the insects, but in captivity they will eat baby mice and lizards, etc. Tarsiers are gentle creatures and are capable of a fair amount of facial expression. From the above characteristics the tarsiers appear to be much closer to the Anthropoidea than do any of the other Prosimii. ANTHROPOIDEA: As many of the early prosimians gradually became extinct at the end of Eocene epoch, new types of primates emerged in tropical forest environments. The divergent evolution of the higher primates is closely linked with plate tectonics and continental drift. The salient features of the sub order Anthropoidea are larger brain in relation to the body size alongwith many other improvements at the same time reduction in the apparatus for the sense of smell. The forward shift of eyes has been completed and the orbits are invariably separated from the temporal fossa by extensive bony partition. The foramen magnum and the joint connecting the skull with the vertebral column lie forward in early stages of development, but subsequently the orbits are invariably separated from the temporal fossa by extensive bony partition. The permanent dentition contain I=2 and C=1, PM=2 or 3, M=2 or 3 on each side of both the jaws which tend to migrate underneath the brain case. The duration of the pre- and post-natal growth tends to become prolonged. The age of sexual maturity is reached rather late in almost all members especially in the higher simian primates. The sub order Anthropoidea is divided into three super family based on their distinct ecological niches. The three super families are the Ceboidea/Platyrrhines all monkeys from America or New World Moneys, Cercopithecoidea/ Catarrhines monkeys or Cercopithecoids from Asia and Africa also called Old World Monkeys and the Hominidea including apes and humans of all over the world).

6 Ceboidea (New World Monkeys): New world monkeys live in tropical forests of South and Central America. They are characterized by flat noses with widely separated, outward-flaring nostrils, from which comes their name patyrrhine (from the Greek for flat nosed ) monkeys. All are arboreal, possessing long, prehensile or grasping tails used as a fifth limb. These features and a dental formula distinguish them from the Old World Monkeys (Cercopithecidae), apes and humans. Platyrrhines walk on all four limbs with their palm down and scamper along tree branches in search of fruit. They eat sitting upright. Although ceboidea spend much of their time on the trees they rarely hang suspended below the branches or swing from limb to limb by their arms. They lack extremely long forelimbs and broad shoulders characteristics of the apes. The superfamily Ceboidea comprises two distinct families, the Callithricidae and Cebidae. Callithricidae: Five genera of monkeys represent the family Callithricidae. The Callithicidae consists of small animals about the size of squirrel. They all have long non-prehensile tail sparsely covered with hair on it s under surface. The tail is usually tufted at the tip. The face is relatively flat with large eyes. Two primitive fovea and macula are present in the retina that is why marmosets are presumed to be capable of stereoscopic vision. The brain is remarkably voluminous in proportion to size of the body. They have well developed frontal lobes which give the skull a very humanlike appearance. The morphology of the lower canine in the genera Callithrix and Cebuella resembles lower incisor teeth known as incisiform canines. Among the genera Saguinus and Leontideus these teeth have the normal caniniform lower canines. The dental formula of the Callithricidae is I 2/2, C 1/1, PM 3/3, M2/2 but of Callimico I 2/2, C 1/1, PM 3/3, M 3/3 and it has an extremely soft, silky black pelage which regard them to be transitional between the marmosets and monkeys. In the family Callithricidae the genus Cebuella is the smallest among the new world monkeys. Cebidae: The family Cebidae consists of 11 genera of monkeys which constitute a varied assortment of animals. The members of Cebidae are larger in size than those of Callithricidae, but not as large as the monkeys of the old world. The dental formula is I 2/2, C 1/1, PM 3/3, M 3/3. All digits bear nails with the exception of the first digit. They are arched or laterally compressed. The long tail is prehensile in only half of the genera namely in Cebus, Alouatta, Ateles, Lagothrix and Brachyteles. In the Uakaris monkeys (Cacejao) the tail is very short. In the spider monkey (Ateles) the forelimbs exceeds the hind limb in length. In the wooly monkeys (Lagothrix) fore and hind limbs are almost equal in length while in the rest of the genera the hind limb exceeds the forelimbs in length.

7 The projections of the jaws are appreciably less than those of the old world monkeys. The surface of the brain is richly convoluted, the fissural pattern bear surprising resemblance to those of the brains of old world monkeys. With the exception of the night monkey (Aotus), as their name implies are nocturnal animals while all the Cebidae possess a well developed fovea and macula capable of stereoscopic vision. All the Cebidae are arboreal in habit and diurnal except Aotus which is smallest among the Cebidae. One young is usually born at a time. The young is carried by the mother on her back, in Samiri and Cebus the father generally carries the infant on his back. The members of Cebidae live in communities with the exception of the night monkeys. Diet varies from genus to genus but is mainly frugivorous; some are insect eaters while the howler monkeys (Alouatta) are mainly leaf eaters. The members of cebidae are comparatively intelligent creatures, gentle, relatively unaggressive, and capable of a very wide range of facial expression. CERCOPITHECOIDEA (OLD WORLD MONKEYS): The Cercopithecoids are mostly represented in Africa while genus Macaca is represented outside the continent in Asia, Gibralter and the genus Cercopithecus (Celebes apes) are native to Celebes Isle. They have been introduced into Asia. These consist of tall quadrupedal monkeys adapted for arboreal way of life. The most numerous, however are the terrestrial varieties. The dental formula of the cercopithecoidea is I 2/2, C 1/1, PM 2/2, M 3/3. The Chief peculiarity is a pair of calloused buttocklike skin pads, or ischial callosities, which support their weighs while they sit. Cecopithecoids have molars with higher and more pointed cusps, connected by sharp shearing crests. The front lower premolars of Cercopithecoids have evolved into an elongated blade that acts as a whitstone, against which the dagger like upper canine is honed to a keen cutting edge. The living cercopithecoids are usually divided into two families- Cercopithecidae and Colobinae on the basis of different feeding adaptations. Cercopithecidae: Cercopithecidae are principally fruit eaters. Like some rodents they have cheek pouches. In these receptacles they are able to cram a great quantity of food which they masticate later at leisure and in safety. Although all Cercopithecines seek safety and shelter in trees many spend most of their time on the ground. The terrestrial habits of many Cercopithecines are widest in their vertebral column and limb bones which approach the forms seen in typical non-primate quadrupeds e.g. a narrow thorax, with a reduced ability to spread the arm. These are a reorientation of shoulder blades and shoulder joints as seen in Patas monkeys. The terrestrial habits of baboons and macaques are reflected in the relatively short fingers which together with the strong and fully opposable thumbs gives the hands a strikingly human appearance. The Guenons (Cercopithecus) are lightly built, long-tailed arboreal creatures of great ability, with short faces and rounded head. The Mangabeys (Cercocebus) are arboreal, very long-tailed, slenderly built, white lidded monkeys and the jaws projects quite prominently. The Macaca are stockily built creatures, the tail is usually short, and the muzzle projecting. The Celebes ape has an extremely reduced tail and a peculiar crest of hair which springs from

8 the crown of the head. The baboons lives in rocky regions and have dog like muzzles. Baboons and macaques are sexually dimorphic in a number of traits. The canine teeth of males are considerably larger than the canines of females. Females of the terrestrial Cercopithecidae have a striking development of the skin during the oestrus cycle. During the oestrus the preanal region of the female swells enormously and turns into brilliant red or reddish pink. Baboons and Macaques have many features that suggest the kind of adaptation which may have been part of the behavioral receptory of early hominids living on the grassy plains of Africa. We can develop hypothesis about trends in the early evolution of human social behaviour by careful study of baboons. COLOBIDAE (LEAF MONKEY): The Colobidae consist of monkeys which are lightly built with long slender tails. They all are arboreal and diurnal in their habits. Colobidae are specialized folivores which evolved stomachs with multiple sub-divisions like those of a cattles. This stores leafy forage for decomposition and digestion by bacteria. Like other folivorous mammals; Calobines do not digest leaves as such instead get the by products of the bacterial colonies in their internal compost heaps without the cheek pouches. Colobines have slender hands and feet. Their thumbs are small or vestigial. These and other features of the Colobine skeleton are parallel among monkeys and apes that habitually use their hands as hooks in swinging from overhead branches. But Colobines seldom do this. Yet the purpose of such specialization to them is unclear. They are all Asian group with the exception of Guerezas of Africa. The Colobidae are characterized by a long and often highly coloured pelage. The true langurs (Simnopithecus) are slenderly built animals with short faces. The snub-nosed langurs (Rhinopithecus) are characterized by retrousses noses, while the proboscis monkey (Nasalis) is notable for the remarkable development of the nose which projects several inches beyond the face below the level of the mouth. The Guerezas (colobus) have short faces, long slender non prehensile tails and external thumbs reduced to a tubercle which may or may not have a rudimentary nail. Among the langurs the males mature later than the females. The male dominance hierarchy is more clearly defined. It is achieved without much fighting and aggression. A new born langur is a focus of attention and social relations of adult females in a troop. Female langurs loan their infants to other females hence the new born has protective contact with many adult females. The male langurs appear to take no interest in the newborns. The differences in the nature of troop organization and social life

9 of various highly organized terrestrial or semiterrestrial monkeys suggest that the general ecological situation may be one of the fundamental determinants of the organization of social life. HOMINOIDEA: The Hominoidea are distinguished from other genera of primates by the absence of a tail, the presence of a vermiform appendix, a very large complex brain, arms which are longer than the legs, a laterally expanded pelvis, chest more or less flattened from front to back, ability to assume an erect posture, locomotion by brachiation or over arm swinging (except in man and adult gorilla). The great apes are obliquely quadrupedal while man in habitually bipedal. The thumb and big toe are opposable in the anthropomorphous apes but in man the thumb alone is opposable. The superfamily Hominoidea comprises four families. They are Hylobatidae, Pongidae, Panidae and Hominidae. HYLOBATIDAE: The representatives of the family Hylobatidae, the Siamang and the gibbon are the most specialized and the smallest of the living apes inhabiting evergreen forest of Southeast Asia. There are five species and nineteen sub species of gibbon whereas the Siamans have two species and nineteen sub species. The hylobatids savor a diverse diet ranging from fruit and leaves to spider and termites. All the hylobatids have relatively short trunk, extremely long slender arms, curved fingers and powerful shoulder muscles. These characteristics enable them to negotiate their arboreal environment through brachiation. Many primates can hang easily from the branches with one hand while feeding or wrestling with a playmate with the other. However, brachiating primates such as the gibbon swing through the tree like acrobats covering up to 30 feet in a single motion. The arms are so long that the finger tips touch the ground when the animal stands erect. The gibbon and siamangs live in monogamous family groups consisting of male-female pairs along with as many as four immature offspring. These young may stay in the group for up to ten years. The Hylobatids are noisy, often calling and vocalizing to signal their presence to other groups. The siamang differs from the common gibbon in the following characters: 1. a larger body weight (24 as against 13 pounds) and larger dimensions of nearly all body parts 2. much shorter trunk and relatively broader chest 3. shorter legs ( in proportion to the trunk) and much larger arms 4. (in proportion to the legs) 5. relatively broader hand 6. a longer skull 7. the common occurrence of supernumery molar teeth 8. the presence of a throat pouch or vocal sac

10 9. scantier body hair and 10. Frequent webbings between the 2 nd and 3 rd toes. PONGIDAE: The Orang-utan is represented by a single species Pongo pygmaeus with two sub-species, confined to the island of Borneo and Sumatra. The Orang-utan has very long arms and short legs reaching a height of slightly over four feet when the animal stands erect its finger tip touch the ankles. The average weight of a male is 165 pounds whereas that of a female is a little over 80 pounds. In the closeness of the eyes and facial prominence, an orangutan looks very humanlike. On the ground they walk with their four limbs in a fist sideways or a palm down position. Skin colour is pale yellowish brown. There is maximum development of laryngeal sacs. There are seven cervical and an average of 12 thoracic, four lumbar, five sacral and three coccygeal vertebrae.the skull exhibits a short rounded brain case and a concave hollowed-out face. This gives the facial profile an S like appearance which has been termed Sinognathism. The nasal bones are markedly reduced in breath sometimes fail to develop altogether. There is no mastoid process. Sagittal crest is present. The forehead is comparatively high and rounded. The average cranial capacity of the male is 410 cc. The movements of the Orang-utan are very slow and deliberate. On the ground an animal moves on all fours in a laborious and shaky manner. In the female menstruation occurs regularly and in some animals there is a definite swelling of the sexual skin during pregnancy. Pregnancy lasts 275 days. One young is born at a time. The Orangutan has a distinctive noyau social organization in which adult males and females do not live in large social group or pairs. Instead, adult females together with their immature offspring range over comparatively small areas searching for leaves, fruits and seeds. Adult males in contrast cover large areas often encountering several females with whom they may mate. PANIDAE: Family Panidae comprises two genera namely Pan and Gorilla. Chimpanzees: Chimpanzees inhabit a broad belt across equatorial Africa from the west coast to Lake Tanganyika in the east. Two species of Chimpanzees have been identified in Africa: the common chimpanzee (Pan troglodytes) and the Pygmy Chimpanzee (Pan paniscus). Chimpanzees are knuckle walkers however they spend a good deal of time swinging in the trees and feeding on all sorts of fruit and vegetation. There are seven cervical and an average of 13 thoracic, four lumber, six sacral and three coccygeal vertebrae. The average weight of the male is 110 pound and the female is 88 pounds. The average height of the male is five feet and of the female four feet. Skin colour varies from entirely white to black as well as brown. Most of the

11 species of chimpanzee have round low vaulted head. The supra orbital ridges are poorly developed but are continuous. The nasal bones are very small. The forward projection of the jaw is clearly visible, canines are large and projecting but they are smaller in comparison to those of Orangutan and the gorilla. The upper extremities are long, the tips of the fingers reaching to the level of the knee-joint. The thumb is opposable. Chimpanzees band together in less structural organizations than those of other anthropoid primates. Primatologist Jane Goodall (1986) observed that male-female sexual bonding among chimpanzees is extremely fluid. One female may mate with a number of males in the group. In other cases, a male and a receptive female may form a temporary sexual bond or consortship and travel together for several days. As Goodall has also noted the fluid nature of chimpanzee social life makes the day-today experiences of a chimpanzee for more varied than those of most other primates. GORILLA: Gorillas found in equatorial Africa are the largest apes; an adult male can weigh over 450 pounds while a female about half that size. There are two subspecies of this genus, the one in the western equatorial lowland or costal gorilla, Gorilla gorilla gorilla, and the other on the east central highland or mountain gorilla, Gorilla gorilla beringri. The body is covered with a thick coat of glossy black hair and mature male have a silvery gray upper back. There is a strikingly human look about the face. Like man they focus on things in their field of vision by directing the eyes rather than moving the head. Gorillas are mostly ground dwellers but the lighter females and young may sleep on the trees in carefully constructed nests. Because of the weight, adult males are limited to raising and lowering themselves among the tree branches when searching for fruit. They are knuckle-walking animals. They stand erect to reach fruits, to see something more easily or to threaten perceived sources of danger with their famous chest beating displays. Although gorillas are gentle and tolerant, bluffing is an important part of their behavioural repertoire. Gorillas rarely fight for food, territory, or sex, but will fight fiercely to maintain the integrity of the group. HOMINIDAE: The family hominidae is represented by Homo sapiens, one of the terminal products of an evolutionary radiation which also led to the development of other types which have now become extinct such as Homo neanderthalensis. As monkeys of the order Primates, humans share physical and anatomical similarities, as well as some behavioural characteristics with other primates. The striking resemblance between the skeletons of a chimpanzee and a human being clearly identifies human as primates. Yet human possesses certain novel capacities and abilities that make them unique, e.g. humans alone walk upright on two legs. Chimps, gorilla and orangutans may stand upright

12 for a short periods, but only human maintain a completely erect posture and consistently walk upright on two legs. The human pelvis, legs, and feet provide the balance and co-ordination that make this type of movement possible. Because human hands are not needed for locomotion, they have evolved into highly precise organs for the manipulation of objects. The facial height is short. It is nearly at right angles to the base of the skull with a wide spheno-maxillary suture. The pre maxilla is not marked of from the maxilla. The snout is absent and the sense of smell is also diminished. However, the power of sight has been increased and we have a stereoscopic vision. The orbits are more or less rectangular. The human skull is a large bony case situated at the anterior or the upper extremity of the vertebral column. It consists of two parts; cranial and facial. The cranium is a large and hollow case which accommodates the brain. The average cranial capacity varies from 1300 to 1415 cc. The human cerebrum referred to in common usage as the gray matter and its outer covering the neo cortex ( the section that controls higher brain functions) are far more highly developed than those of other primates, allowing humans to engage in complex learning, abstract thought, and the storing and processing of vast amounts of information. The size and complexity of the human brain together with the protracted period of dependence and maturation characteristic of young humans, stand as the most significant differences between humans and other primates and give rise to the formers extra ordinary capacity to learn, to their imaginative social interactions and to their facility-unique among all life forms to use and produce symbols, language and culture. CONCLUSION: The science of classification gives scientist a convenient way of referring to and comparing living and extinct organism. A brief history of classification along with evolutionary pattern has been given. All the living organisms in the order primates share many common characteristics but they also share a great deal of variation, hence they are divided into suborder, superfamily, family and genus, etc. and each one among them shares common characteristics than with others. All criteria of relationships are based upon essential identities of structure and development, which are called homologies, not upon the deceptive similarities due to function, which are called analogies. Although there are differences in opinion regarding the criteria to define a species, there is a general agreement in the divisions. The classification after Campbell and Loy 1966 has been adopted for the inclusion of Homonoidea as a superfamily under the suborder Anthropoidea instead of inclusion under cercopithecoidea. The evolutionary trend among the primates based on comparative morphology skull, dentition, social habit, food habit, physiology, distribution, life history, anatomy etc are taken into consideration in the classification of primates starting from prosimian to Hominoidea.