What are Primate ?
Primates Members of the mammalian order . Primates, which includes lemurs, lorises, tarsiers, monkeys, apes, and humans. Primatologists have drawn attention to a group of characteristics that, when taken together, more or less characterize the entire primate order.
The following list is meant to give you a general anatomical and behavioral picture of the primates. In their limbs and locomotion, teeth, diet, senses, brain, and behavior, primates reflect a common evolutionary history with adaptations to similar environmental challenges, primarily as highly social, arboreal beings.
A. Limbs and Locomotion
- 1. A tendency toward an erect posture (especially in the upper body). All primates show this tendency to some degree, and it’s variously associated with sitting, leaping, standing, and, occasionally, bipedal walking.
- 2. A flexible, generalized limb structure, which allows most primates to practice various locomotor behaviors. Primates have retained some bones (such as the clavicle, or collarbone) and certain abilities (like rotation of the forearm). Various aspects of hip and shoulder anatomy also provide primates with a wide range of limb movement and function. Thus, by maintaining a generalized locomotor anatomy, primates aren’t restricted to one form of movement. Primates also use their limbs for many activities besides locomotion.
- 3. Prehensile hands (and sometimes feet). All primates use their hands, and frequently their feet, to grasp and manipulate objects. This ability is variably expressed and is enhanced by several characteristics, including:
- a. Retention of five digits on the hands and feet. This trait varies somewhat throughout the order, with some species having reduced thumbs or second digits (first fingers).
- b. An opposable thumb and, in most species, a divergent and partially opposable big toe. Most primates are capable of moving the thumb so that it comes in contact with the second digit or with the palm of the hand .
- c. Nails instead of claws. This characteristic is seen in all primates . All lemurs and lorises also have a claw on one digit.
- d. Tactile pads enriched with sensory nerve fibers at the ends of digits. This characteristic enhances the sense of touch.
B. Diet and Teeth
- 1. Lack of dietary specialization. This is typical of most primates, who tend to eat a wide assortment of food items. In general, primates are omnivorous.
- 2. A generalized dentition. Primate teeth aren’t specialized for processing only one type of food, a trait related to a general lack of dietary specialization.
C. The senses and the brain.
Primates (diurnal ones in particular) rely heavily on vision and less on the sense of smell, especially compared with other mammals. This emphasis is reflected in evolutionary changes in the skull, eyes, and brain.
- 1. Color vision. This is a characteristic of all diurnal primates. Nocturnal primates don’t have color vision.
- 2. Depth perception. Primates have stereoscopic vision, or the ability to perceive objects in three dimensions. This is made possible through a variety of mechanisms, including:
- a. Eyes placed toward the front of the face (not to the sides). This position provides for overlapping visual fields, or binocular vision .
- b. Visual information from each eye transmitted to visual centers in both hemispheres of the brain. In nonprimate mammals, most optic nerve fibers cross to the opposite hemisphere through a structure at the base of the brain. In primates, about 40 percent of the fibers remain on the same side, so that both hemispheres receive much of the same information.
- c. Visual information organized into three- dimensional images by specialized structures in the brain itself. The capacity for stereoscopic vision depends on each hemisphere of the brain receiving visual information from both eyes and from overlapping visual fields.
- 3. Decreased reliance on the sense of smell. This trend is expressed as an overall reduction in the size of olfactory structures in the brain. This is related to an increased dependence on vision.
- 4. Expansion and increased complexity of the brain.In primates, this expansion is most evident in the visual and association areas of the neocortex (portions of the brain where information from different sensory modalities is combined).
D. Maturation, learning, and behavior
- 1. A more efficient means of fetal nourishment, longer periods of gestation, reduced numbers of offspring (with single births the norm), delayed maturation, and extension of the entire life span.
- 2. A greater dependence on flexible, learned behavior. This trend is correlated with delayed maturation and longer periods of infant and child dependency on at least one parent. Because of these trends, parental investment in each offspring is increased; although fewer offspring are born, they receive more intense rearing.
- 3. The tendency to live in social groups and the permanent association of adult males with the group. Primates tend to associate with other individuals.
- 4. The tendency toward diurnal activity patterns. This is seen in most primates. Lorises, tarsiers, one monkey species, and some lemurs are nocturnal; all the rest (the other monkeys, apes, and humans) are diurnal.
Summery
The following are the main characteristics of the primates:
- The anatomy of Primates enables them to maintain semi-erect and erect postures and locomotor patterns.
- They have pentadactyl hands and feet (a very primitive trait).
- They have flattened nails on each of their digits excepting tree shrews.
- They possess a relatively low density of body hairs (hair instead of fur).
- They have fewer tactile hairs.
- The olfactory area of their brain is reduced. They thus have an increased dominance of vision over smell, and reduction in the length of the (nose) snout
- The visual area of their brain is expanded.
- Their eye sockets are completely encircled by a bony ridge. Their eyes are more forwardly directed on the skull (for binocular vision) suggesting development of a stereoscopic vision.
- They show an increased reliance on stereoscopic vision at the expense of smell (the dominant sensory system in majority of the mammals).
- Some primates have developed a three color vision.
- They have pseudo-and true-opposability of the thumb and the great toe (i.e., the two function, to a varying degree, independently of the other digits.
- They are widely separated from them); usually they have both these digits, on hands and feet, opposable for grasping purposes.
- Some have prehensile tails.
- They possess relatively larger and complex brains.
- Most female primates have a simple unicornuate uterus.
- They are placental mammals with longer gestation period and generally give birth to only one or two infants at a time.
- They have year round fertility.
- Their infants have prolonged physical and emotional dependence upon their mothers, i.e. they have a longer period of infant dependency and parenting.
- They have prolonged growth and maturation periods and long life spans.
- They display a reduction in the number of teeth, i.e. they have an incisor and premolar less in each half of the upper and lower jaws unlike those in the primitive placental mammals.
- They have retained a primitive clavicle.
- They possess a separate radius and an ulna in the forearm and a separate tibia and a fibula in the lower leg (excepting tarsier).
- They show reduction in the length of their external tail.
- They possess a shortened vertebral column.