22 Description and Identification of the disarticulated skeleton of primates

Ms. Sangeeta Dey and Prof. A.K. Kapoor

Contents:

1. Introduction

2. Characteristics of the Primates

3. Non Human Primates

4. Classification of Order Primates

5. The Prosimians

5.1 Tarsiiformes

5.2 Lorisiformes

5.3 Lemuriformes

6. The Anthropoids

6.1 Platyrrhine (The New World Monkey)

6.2 Catarrhine ( The Old World Monkey)

7. The superfamily – Cercopithecoidea

7.1. Guenons

7.2. Mangabeys

7.3. Baboons and Macaques

7.4. Langurs

8. The superfamily – Hominoidea

8.1. Hylobatidae – Gibbons

8.2 Pongidae – Orangutan, Chimpanzee and Gorilla

8.2.1 Orangutan

8.2.2. Chimpanzee

8.2.3. Gorilla

9. Anatomical similarities and dissimilarities between human and non-human primates

Learning Objectives:

To describe the physical Characteristics of the Primates
To understand the Non Human Primates and their skeletal features
To describe and identify and distinguish between prosimians and anthropoids
To know about facts of Gibbons, Orangutans, chimpanzees and gorillas.

1. Introduction

The first radiation of primate order has its roots in the beginning of the explosive adaptive radiation of placental mammals. The earliest discovered traces suggesting the beginnings of our order came from late cretaceous period about 70 million years ago probably early paleocene. The fossil form, purgatorius recovered and exhibit the primate tendency towards a bulbous cusp pattern in the molar teeth compared to the sharper cusps seen in insectivores. Such a dental pattern apparently indicates that early primates were adapting to fruit and leaf-eating diets or perhaps a diet also including insects exploited in an arboreal niche. Paleocene and early Eocene archaic primates have been found in both Europe and North America. However, very limited numbers of skeletal fossil remains have been discovered from Oligocene epoch. Most of the remains are from Africa. The Egyptian varieties include Parapithecus, Propliopithecus, Aegyptopiyhecus.

2. Characteristics of the Primates

The Primates bear flat nails upon their digits. This makes the grasping function of the hands and feet easier.
The presence of well developed clavicle is a characteristic feature of the primates.
The orbits are completely surrounded by bony rims.
The limbs are prehensile and adapted for arboreal life. This was probably an earliest mammalian characteristic.
Either the thumb or the great toe or both are opposable. This possibility, which is an ancient mammalian feature, has been retained by the primates during their long arboreal life.
The teeth are adapted for mixed food-vegetation and animal. Three kinds of teeth are present in the primate, atleast at one time of its life. The teeth are differentiated into incisors, canines and molars to serve different functions of cutting, holding and grinding, etc.
In the primates, the mammae are two in number and they are pectoral in position. The nursing habits of the mother determine the position of the mammary glands.
The development of the brains of the primates shows wide variation. But a calcarine fissure and a posterior lobe is always present in the primate brain.
The primate possess pendulous penis. The character is shown by some other mammals also.
They have a well developed caecum that is a sac connected with the intestine of an animal.
The stomach is simple.
The femur has never third trochanter.
The testes are descended into the scrotum. Of course, it is present in many other agile and active mammals also.

3. Non – Human Primates

When Linnaeus set up a group including lemurs, monkeys, apes and human in his 1758 classification of the mammals, he chose to name it the Primates, a medieval Latin word meaning ‘chieftains’. He had human beings clearly in his mind when he gave this name. The primates derive not only the name but also most of the scientific interest from the fact that human beings are primate. Thus, apart from the humans, all the species in the order primate are considered as non-human primates whether it is apes or monkeys. Biologists since Darwin have studied primates or non-human primates with an eye to their relationship to human beings. Non human primates provide insights in evolutionary trend through comparison of the approved tendencies towards big brains, reduced ability to smell or olfaction, increased manual dexterity, upright posture and other comparable human characteristics.

Classification of Order – Primates

The Prosimians

There are three major infra-orders in the prosimian sub-order. These are –

Tarsiiformes
Lorisiformes
Lemuriformes

5.1. Tarsiiformes

The tarsier is the only remaining member of the once large Tarsiiformes infra-order. These tiny creatures, which live in Borneo and the Philippines, are equipped with a very long tail and hind limbs for hoping from branch to branch. Their huge eyes and the pads at the ends of their fingers add to their strange frog like appearance. The special pads help them cling to smooth, vertical surfaces. During the day, they sleep clinging to a vertical branch. They wake at dusk and spend the evening hopping from tree to tree looking for insects and lizards to eat.

Skeletal features:

In the skull, the post orbital wall is present. The orbits are very large and completely directed forward. The lachrymal foramen is outside the orbit. The bulla is large and inflated. The tympanic annulus is outside the auditory meatus. The typical dental formula is I 2/2 : C1/1 : PM 2/2 : M 3/3. The tibia and fibula are fused together at their lower ends.

5.2. Lorisiformes

Nocturnal primates, Lorisiformes are divided into two distinct types – Lories and galagos according to their locomotor patterns. Lorises are found in Sub-Saharan Africa and in Asia. They are adapted to slow climbing and creeping. This movement is made possible by a very powerful grasp and strong muscles. Lorises can hang by one hind limb while reaching for food. Insects seem to form the bulk of their diet, but they will eat almost anything from flowers to young birds. Galogos by contrast, leap gracefully through the trees, taking long kangaroo like hops with their strong hind limbs. Their shorter forelimbs are used to grab hold of branches when they land. They can easily leap from one vertical support to another. Galagos range from the size of large mice to the size of large rabbits. Like the Lorises, They are omnivorous and thus eat both plants and animals.

5.3. Lemuriformes

The lemuriformes which include lemurs are found primarily on the island of Madagascar, off the southeast coast of Africa. They have developed many variations because of the lack of competition and predators. The member of one genus, the mouse lemurs, are smaller than a mouse and they are the tiniest living primates. Most lemuriformes are active during the day and at dusk but some are nocturnal. Most are completely arboreal and are wonderful acrobats. They can leap greater distances is due not only to their musculature but also to unusually well-developed binocular vision. Unlike other prosimians, the lemurs avoid animal foods and seem to be highly social. Lemurs live in troops of up to 60 members and sleep cuddled in small groups with their tails wrapped around one another.

Skeletal features:

In the skull, the post orbital wall is absent. The eyes are directed outwards. The lachrymal foramen or the tear duct is outside the orbit. In the inner wall of the orbit portion of the palatine bone is present. The skull is not balanced upon the vertebral column, but is suspended from occipital condyles. The external auditory meatus is absent. A large spherical auditory bulla is present. The jaw is elongated to give it fox-like appearance. The typical dental formula is I 2/2 : C1/1 : PM 2/2 : M 3/3.The canines and the incisors are placed in front of the jaw in a row like the teeth of a hair comb. These are separated from the first premolar by a gap.

6. The Anthropoids

The anthropoids are also a diverse suborder. But they are characterized by their own shared set of specialized adaptations. These adaptations mainly allow a more effective use of arboreal environments. Forward-facing eyes permit stereoscopic vision among the anthropoids, and the visual centers of the brain are complex, allowing integration of large amounts of visual data. Depth perception and quick reaction to visual cues are essential to tree-living. Anthropoids also possess colour vision, which aids in depth perception and the sighting of brightly coloured fruit in trees. Adaptations for grasping and handling objects are crucial to life in trees, as well. Finally, the characteristically high brain to body ratio of anthropoids increases their ability to survive by agility and learning. These qualities are more appropriate in the trees than are the specializations of terrestrial animals for attack and defence such as large horns, tusks and claws.

6.1. Platyrrhine (The New World Monkey)

The new world monkeys live throughout the heavily forested regions of Central and South America. They are divided into families: Callithricidae, which include the marmosets and tamarins, and the Cebidae which contains six subfamilies. Most new world monkeys belong to Cebidae.

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Most new world monkeys seem to spend their lives in the trees. They do not come down even for water. Apparently they get enough moisture from the flowers, fruits, and nuts they eat. Locomotion patterns vary among the new world monkeys. Some walk on all fours both on the ground and on tree branches. Others can also move in an upright position. They do so by swinging from their arms, which are longer than their legs. Some use their strong prehensile tails to swing and to grasp limbs as they pick fruits. They can jump as far as 30 feet. They have been seen in troops of up to 30 and in family bands.

6.2. Catarrhine ( The Old World Monkey)

Within the Catarrhine line, there are two super families – Cercopithecoidea or the old world monkeys and Hominoidea (Humans, apes, gibbons, orangutans, chimpanzees and gorillas) The major differences that have evolved between these two groups are:

Most species of old world monkeys have tails; hominoids have no tails.
Old world monkeys have prenatal development of ischial callosities. Most hominoids are not born with these rump pads although they may grow after birth.
Old world monkeys have a shorter life span than the hominoids.
Old world monkeys have smaller brain size to body weight ratios as well as less complex brains than the hominoids. The cerebral cortex is especially well developed in hominoids.

7. The superfamily – Cercopithecoidea

The superfamily Cercopithecoidea contains a single family, which can be divided into two subfamilies, the Cercopithecinae and the Colobinae. The most common genera in the Cercopithecinae are – guenons, mangabeys, baboons and macaques. Langurs are the most common genus in the Colobinae subfamily.

Skeletal features: All species possess ischial callosities. All digits with more perfectly flattened nails. The tail is not prehensile. The nostrils are situated close to each other. The bregma is placed relatively far forwards. The pre-maxilla is extended up to the nasal opening. Sometimes it touches the frontal bone. The jugal never articulates with the parietal bone. The palate is relatively long. The basicranial axis is comparatively short. The auditory bulla is absent. The tympanic annulus is elongated and it forms external auditory meatus. The typical dental formula is I 2/2 : C1/1 : PM 2/2 : M 3/3. The upper premolars are three rooted and the lower are two rooted.

7.1. Guenons

The cercopithecine monkeys or guenons are widely distributed in Africa. Although they live mostly in trees, some species come down to feed on the forest floor, in plantations, in open bush, and in savanna country. They live largely on insects, fruits and vegetation, but will sometimes eat birds, bird eggs and even small mammals. They seem to live in small groups made up of a dominant male and small harem of females and their children.

7.2. Mangabeys

The long-tailed mangabeys that are sometimes seen with cercopithecines spend much of their day on the ground. Through they possess some adaptations to life on the trees, they also have some of the traits of terrestrial primates. Their hands, for instance, are more like those of the terrestrial baboons than those of totally arboreal primates. They live mostly in the swampy forests of Africa.

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7.3. Baboons and Macaques

Baboons and macaques are closely related though classified as separate genera. If they mate, they can sometime produce fertile offspring. But they inhabit different ranges. The baboons live in Africa and the Arabian Peninsula. The macaques range from India east to Japan. They both live mainly on the ground, though they sleep in trees. Both have developed finely controlled hands with precision grips that function like ours.

7.3. Baboons and Macaques

The baboons live in highly structured troops of 10 to 100 members. Within the troop a clear dominance hierarchy reduces tensions and provides protection from predators.The threat of predators may be the reason for their extreme sexual dimorphism. The males are specialized for defence on the ground. They are twice as big as the females and they can put on impressive threat displays with their huge canine teeth and their great ruffs of fur at the neck.

7.4. Langurs

Langurs are slender, long tailed Asiatic monkeys. They often feed on the ground but prefer graceful flight into the tress rather than an organized show of force. Group organization is not as important for defence. Langurs sometimes live alone and sometimes in troops. The relationship between males and females are not well defined. The status of females is high when they are paired with a male. But when their infants are born the mothers seem to drop out of the status system altogether. When dominant males are found near temples, they form harems (group of females) and actually chase away other males.

8. The superfamily – Hominoide

The superfamily – Hominoidea includes three family – Hylobatidae which represent gibbons; Pongidae which includes orangutan, Chimpanzee and gorilla and Hominidae that is human beings.

8.1. Hylobatidae – Gibbons

Gibbon is one of the smallest apes inhabiting South East Asiatic Islands, viz., Java, Sumatra, Borneo, and Philippines. They are also seen in Southern China. There are about 12 varieties of gibbon. The height of the gibbon does not exceed 3 feet and the weight of the adult gibbon ranges from 11 to 15 pounds. There is no sexual dimorphism with regards to the size. The body of these animals covered with fine wooly hairs, whereas, the hairs of gorilla, chimpanzee, and orang-utan are coarse. The colour of the hair is white, gray and sometimes black or a combination of these three colours.

At times, gibbons can stand erect. The arms are excessively long in comparison to the length of the leg. It is said that during erect position, the finger tips of the gibbons generally touch to the ground. The gibbon can pick up any material from the ground without stooping. Due to their adaptation to arboreal conditions, the hands of the gibbons, especially the radius and the ulna (fore arm bones) have elongated enormously. The hand is very long and narrow with a relatively short thumb, which is not perfectly opposable. With the help of the light and slender body, powerful arms provided with long fingers and short thumb, the gibbon can easily travel through the trees with a free swinging and pendulum motion. In length of the leg, as compared to the trunk, the gibbon exceeds all other anthropoids and stand next to man. The foot is elongated and narrow. The great toe will be found far apart from other digits. This wide separation has an advantage in grasping the branches of the tree.

The cranium is enlarged and slightly flattened, while the facial portion is reduced in size. The cranium presents ovoid contour and low frontal elevation. The orbits are large and prominent; the supraorbital torus is absent. The nasal bones are flat and broad. The nasal aperture is ovoid. The mastoid and the styloid processes are not developed. The bregma is situated far back on the roof of the cranium. The dental characters show sexual differentiation. The canine is large, sharp and pointed and it interlocks on closure of the jaws. The cranium length of the gibbon is 7.5 cm. The cranial capacity varies from 76 – 90 CC. It is greatly below than that of the higher apes, but higher than those of the monkeys.

The gibbons are gentle and pleasant and they live in families, which are composed of the parents and the minor children. They can be kept as pets. Their food consists of fruits, leaves, buds, eggs, different kinds of insects and smaller birds. The gibbons possess ischial callosities which is the characteristics of Old world monkeys. In males, the ischial callosities are widely separated into two halves.

8.2. Pongidae – Orangutan, Chimpanzee and Gorilla

8.2.4. Orangutan

The orangutan differ very much from the gibbons in their bulky and heavy bodies. They are found mostly in the islands of Borneo and Sumatra. In erect position, the animal is nearly 5 feet high. The weight of the adult males varies from 165 to 200 pounds. The females are somewhat higher. The body of orang-utan is covered with long, coarse hairs of reddish brown colour. No hair is found on the face, ears, palm and soles. The chest is barrel like. The breasts are laterally situated near the armpits. In profile the nose gives a flat, concave appearance as the root is narrow and the bridge is not elevated. The face is concave in profile. Such a condition of face is described as ‘sinognathism’. The arms are long and narrow with elongated fingers. The thumb is small and all the digits have flat nails. The forearm is much longer than the upper arms. The legs are short and the foot is long and narrow. When the orangutan is kept in erect posture the fingertips reach the ankles. The great toe is opposable and very small.

The skull is distinguished by its relatively small braincase and enormous facial portion. The average cranial capacity is 416 CC. The orbits are elliptical in shape. The supraorbital ridges are not continuous and as such no torus is formed. The forehead is high and rounded. The nasal bones are extremely small and these are fused together even in young animals. The mastoid process is not developed. There is no styloid process. The glenoid fossa is shallow and the post glenoid tubercle is large. The external auditory meatus is not much prolonged. The jaw is of enormous size and is projecting forward. The chin is absent. The dental characters show sexual differentiation. The canines are long, sharp, tusk – like and are interlocking. They have 12 pairs of ribs as in man as against 13 pairs in the gibbon, gorilla and chimpanzee.

The orangutans are arboreal in nature. They live on trees by building nests on the branches. They walk on all four extremities when they come to the ground. The whole body of orangs is built in such a manner that it can enjoy the arboreal life to a lesser degree than the gibbon, but to a higher degree than the other two apes. The food of the orangutan consists of fruits, different varieties of leaves, insects etc. The orangutan is represented by a single species.

The skull of the orangutan is distinguished from that of a gibbon by its absolute larger size. It differs from those of the gorilla and chimpanzee by

the large jaw in relation to the skull
splint-like nasal bones and sinognathous face
non-continuous supraorbital ridges

8.2.5. Chimpanzee

The body of the chimpanzee is not so well built as in the case of the orangutan and the gorilla. The chimps are found in large numbers in the tropical forests of Africa. There are three species of chimpanzees – the common chimpanzee, the black-faced, bald-headed chimpanzee and the pygmy chimpanzee. The body proportion of chimpanzee shows some tendency toward that of man. The average height of the full grown common chimpanzee is 5 feet. The weight of the adult male and female are 110 and 88 pounds respectively.

The body is covered with loose and coarse hairs of various colours. There are no hairs on the face, hands and feet. The head of the bald-headed chimpanzees are devoid of hairs. Most species of the chimpanzees have round low vaulted heads. The average cranial capacity is 400 CC. There is a poor development of the supraorbital ridges and it is continuous and prominent but not so massive as in the gorilla. The nasal bones are very small, the bridge is not elevated with the tip of the nose is not like that of the man. The external auditory meatus is prolonged and tubular. The glenoid fossa is shallow in comparison to that of gorilla with the postglenoid region is well marked. In chimpanzee the forward projection of the jaw is evident. The canines are large and projecting but are smaller in comparison to that of the orangutans and the gorilla. The chin is absent and the lips are thin. The general appearance of the skull is oval however the facial region is small in proportion to the skull. The orbits are elliptical but not so as we encountered in the case of the orangutans.

The hands of the chimpanzee are elongated and narrow. The fingers are long and the thumb is small opposable. The legs are long and these are larger than those of the orangutan. The foot is long but the hind limbs of chimpanzee are poorly adapted for walking upright. The great is opposable and it is not in line with the other toes. The heel is rudimentary and in erect position the hands of the chimpanzee generally reach up to the knee-level.

The chimpanzees are experts in climbing and brachiating. They build nests on the trees and sleep there during the night. Their food consists of fruits, different vegetable products, eggs, small birds and sometimes rodents.

8.2.6. Gorilla

Among all the non- human primates, the gorilla is the largest and the stoutest. They are found in equatorial regions of Africa. The gorillas are represented by two species – the Western Coastal or the lowland gorilla and the eastern or mountain gorilla. The former inhabit mainly in the regions of Cameroons while the latter is found in the region of the Eastern Congo, west of Lake Edward and Lake Kivu. When the gorilla stands erect, the hands go below the knee joint. The height ranges from 5 feet to 6 feet in the lowland gorillas and 5 feet 3 and a half inches to 5 feet 11 inches in the mountain gorillas. The weight of the body of adult males ranges from 350 to 600 pounds.

The body is covered with long and black coloured hairs. The face, palms and soles are completely devoid of hairs. The massive skull of the gorilla is a note worthy feature. The head is very large but consist of smaller cranium with enormous and projecting face and jaw. The supraorbital ridges above the eye openings are of enormous size and it goes from left to right of the skull. It is continuous to form a torus. The forehead is very low. The general appearance of the skull is more or less oval and there is a prominent sagittal crest. It is weaker in females. The average cranial capacities of the males and the females are 550 CC and 450 CC respectively. The big cranium consists of solid bones and there is little space for the brain. The facial portion is larger in proportion to the cranial part. The jaws are large and projected forward and downwards. The upper jaw is prognathus and the lower jaw is massive. The size of the canines is enormous and they interlock. The nasal bones are long, low and narrow; the bridge is slightly elevated. Nostrils are broad and forwardly directed and these are covered by cartilaginous rings mostly like nasal wings but not so developed as in man. The lips are thin and chin is completely absent.

The gorilla is more human in different features than in other anthropoid apes. The upper arms are longer than the forearms and therefore it is different from gibbon, orangutan and the chimpanzee. The hand is shorter and broader than in other apes and the thumb is well developed. On the whole, the hand of the gorilla resembles more that of man than any other apes.

The leg is short. The foot of the gorilla also resembles that of man in many respects. The thumb is opposable and it is set apart from the other digits. The heel is more or less well developed. The anatomy of foot of the gorilla speaks that it is less adapted for arboreal prehension. The gorillas spend most of their time on the ground. They climb on the trees also, build their nests and pass the nights there. Sometimes they can walk erect but their usual gait is obliquely quadrupedal.

The mountain gorilla differs from the lowland gorilla in the following characteristics – narrow skull, longer trunk, larger face, shorter limbs, shorter and broader hands, body covered by thick and black coloured hairs.

9. Anatomical similarities and dissimilarities between human and non-human primates

Gorilla and Man: In hands, feet and pelvis and in the size of the brain, the gorilla shows close relationship with man. But the massive jaws of the gorillas have no resemblances with those of man.
Chimpanzee and man: The chimpanzee and man relate to each other to a greater extent by means of the likeness of the skull and the pigmentation of the body. The chest proportion of chimpanzee is mostly human.
Orangutan and Man: With respect to high forehead and the same number of pairs of ribs, the orangutan demands a closer relationship with man, than all other apes. On the other hand, the two factors like the shortness and degenerate characters of the legs and the adoption of the feet for suspension, separate these two individuals from each other.
Gibbon and Man: The length of legs and the erect gait of the gibbon indicate its closer relationship with man anatomically. But in characters like excessive arm lengths, general size, pelvis, hands and feet, length of canine teeth and the size of the brain, the gibbon goes farthest from the man.

It is very difficult to identify the man’s closest relative among the four non-human primates or apes. This is especially true when all the physiological, anatomical, morphological, anthropological and genetic characters are considered.

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