The primate characters reveal their usefulness in locomotion in terms of terrestrial and arboreal adaptations. An examination of their locomotory patterns ‘ reveals how the primates have shifted their locomotory pattern from climbing and clinging to bi-pedal locomotion.
Primate skeleton is basically a generalized one. The skeleton has retained a relatively large number of traits that existed in the early ancestral mammals. At the same time many ancestral features have been replaced by a number of specialized ones. This difference can be seen in the traits that play a role in the movement.
i) Forelimb – Forelimb structure of primates corresponds well to the generalized limb structure of early placental ancestors. For example, all primates have retained clavicle, two separate bones namely radius and ulna in the lower arm and penta dactylism. This permits a greater flexibility in the shoulder, fore arm and hand, which facilitates movement through the tree.
ii) Flexible Skeleton : Primates have a more flexible skeleton and consequently wide range of locomotion patterns, both in trees and on ground.
- (a) Graspino big toe – It is one of the most important characteristic features of the primates except humans and to some extent Orang-utan. Matt Cartmill postulates that more than locomotion this plays a role in arboreal insect predation i.e., to catch insects with hand while holding onto one branch with feet. The adaptation for arboreal niche served to differentiate the early primates from the early mammalian stock.
- (b) Grasping thumb – Many primates have this. In many cases the thumb has become truly opposable. This is also important for manipulating objects.
- (c) Claws have evolved into nails in most primates.
- (d) Tactile pads – Fingers of primates end in tactile pads. These pads act as friction pads in grasping and confer refined sense of touch that helps convey information about the environment.
iii) Senses-
- (a) Smell – In terrestrial mammals olfactory sense plays a crucial role. Smells are relatively unimportant in the trees as most odours hug the ground and the wind as it blows through the trees eliminates their usefulness. Olfactory sense does not indicate useful information (for arboreal environment) like the exact direction and distance between two branches. Therefore, the olfactory region of the brain is reduced and the muzzle or snout is relatively small.
- (b) Vision – Most mammals have 2D black and white vision with increased dependence on olfactory sense but vision in most primates is 3D colour. Primate vision develops in response to the selective pressures of the arboreal environment where precise information of direction and distance is crucial. Excellence in vision combined with fine motor coordinative and manipulative ability permits the development of a superb hand-eye coordination.
- (c) Bonv eve socket – Most primate eyes are encased in bony eye sockets. Complete eye socket is not present in the pro-simiians though they have a bony ring that completely encircles the eye.
- (d) Situation of eves – over many generations, eyes have come to lie on the front of the face permitting 3D stereoscopic vision.
- (e) Stereoscopic vision – Their eyes lie on the front of the face. Stereoscopic vision enables the arboreal primate to determine distance with a high degree of precision, which aids in moving rapidly through the trees. 3D Vision improves the accuracy of the final strike when the primate is pursuing a fast moving insect prey. Vision plays a key role in primate communication i.e,, they communicate largely through visual stimuli although vocalizations also play important rotes.
- (f) Teeth – Primates have fewer teeth than in the ancestral placental mammal, which has 44 teeth. Most higher primates including humans have 32 teeth. Primate teeth are relatively simple in structure compared to teeth of grazing animals and carnivores.
(iv) Placenta:
- (a) Epitheliochorial Placenta – Blood vessels of foetus and mother come into close contact and nutrients and other substances must pass through two vessel walls from eaternei to foetal blood stream. Hemochorial Placenta (Most primates) – Foetal blood vessels penetrate the lining of the uterus. Uterus undergoes cellular changes and the fine blood vessels of the mother break down to form a spongy, blood filled mass. Consequently, foetal blood vessels are surrounded by natural blood, so materials pass through only a single vessel wall in moving from one blood system to another. Primates usually give single births.
- (b) Longer life span – Among mammals, longevity is related to body size. With the larger mammals in general living longer than smaller ones yet when other mammals of similar size are compared with primates, the latter tend to exhibit longer life spans.
(v) Longer life span – Among mammals, longevity is related to body size. With the larger mammals in general living longer than smaller ones yet when other mammals of similar size are compared with primates, the latter tend to exhibit longer life spans.
( vi) Longer life cycle events – Primates have longer life cycle events. A comparison of the life cycle events of primates and non -primates reveals the fact. This is shown in the following table:
| Events | Impala ( loafedmammal) | Coyote (Carnivore) | Chimpanzee(Primate) |
| Gestation period (in days) | 191 | 63 | 224 |
| Age at which female givesbirth to her first off spring( in years) | 2 | 3 | 14 |
| Life span ( in years) | 12.5 | 16 | 41 |
(vii) Intelligence – Primates are known for their great intelligence which is related partly to their great awareness of the environment and their abilities to manipulate their environment. Non -human primates do well on various psychological tests. The following two features of brain permit a great degree of behavioural flexibility in them:
- (a ) Primate brain is large in relation to body size.
- ( b) Areas in the brain that control complex behavioural patterns are well developed.
(viii ) Learning – Much primate adaptability is the result of behavioural adaptation that are learned . Most primates live in large social units and have long childhood periods; these factors facilitate learning.