Primates are members of the vertebrate class: Mammalia, there are over + 4000 mammals. Primates are part of the subgroup of placental mammals.

Three types of primates

• Prosimians (pre-monkeys)
• Monkeys (Old World and New World)
• Apes

Characteristics

to differentiate primates as a distinct group from other mammals, we need to describe those characteristics that, taken together, set primates apart. primates have remained quite generalized. This means that primates have retained several ancestral mammalian
traits that some other mammals have lost over time. Primates can’t be defined by one or even a few traits they share in common because they aren’t so specialized.

General characteristics common to class mammalia-

• body hair,
• a relatively long gestation period followed by live birth,
• mammary glands (thus the term mammal),
• different types of teeth (incisors, canines, premolars, and molars) ie Heterodontism
• the ability to maintain a constant internal body temperature through physiological means, or endothermy and Homeothermy
• increased brain size, and
• a considerable capacity for learning and behavioral flexibility.

Characteristics of Primates

• Difficult to define by one or two common traits
• Primates are generalized (rather than specialized) mammals.
• Defined by evolutionary trends
• Not all traits found in every member of the order.

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 animals.

Characteristics of Primates:
Limbs and Locomotion

• Tendency toward erect posture.
• Flexible, generalized limb structure
• Engage in a number of locomotor behaviors.

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 generalized limb structure, which allows most primates to practice numerous forms of locomotion. Various aspects of hip and shoulder anatomy 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, like many other mammals are. Primates also use their limbs for many activities besides locomotion.

Hands and Feet

• High degree of grasping ability.
• 5 digits on hand and feet.
• Opposable thumb and partially opposable great toe.
• Tactile pads enriched with sensory nerve fibers at the ends of digits.
• Prehensile hands (and sometimes feet).

Many animals can manipulate objects, but not as skilfully as primates . 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:

1. 1. 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).
   2. 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 .
   3. Nails instead of claws. This characteristic is seen in all primates except some New World monkeys (marmosets and tamarins). All lemurs and lorises also have a claw on one digit.
   4. Tactile pads enriched with sensory nerve fibers at the ends of digits. This characteristic enhances the sense of touch.

Diet and Teeth

• Lack of dietary specialization and tend to eat a wide variety of foods.
• Generalized dentition, teeth are not specialized for processing one type of food.

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.

Senses and the Brain

Primates (diurnal ones in particular) rely heavily on vision and less on the sense of smell, especially when compared with other mammals. This emphasis is reflected in evolutionary changes in the skull, eyes, and brain.

• Color vision (excerpt for nocturnal primates)
• Depth perception
• Decreased reliance on the sense of smell (olfaction)
• Expansion and increased complexity of the 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:
   1. Eyes placed toward the front of the face (not to the sides). This position provides for overlapping visual fields, or binocular vision .
   2. 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.
   3. 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. Corresponding reduction of the entire olfactory apparatus has also resulted in decreased size of the snout in most species. This is related to an increased dependence on vision. Some species, such as baboons, have large muzzles, but this isn’t related to olfaction, but rather to the need to accommodate large canine teeth.
4. Expansion and increased complexity of the brain. This is a general trend among placental mammals, but it’s especially true of primates . 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).

Maturation, Learning, and Behavior

• Longer gestation, fewer offspring, delayed maturation, and longer life span.
• Greater dependence on flexible, learned behavior.
• Tendency to live in social groups.
• Tendency for diurnal activity patterns.

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 subsequently longer periods of infant and adolescent 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 parental care.
3. The tendency to live in social groups and the permanent association of adult males with the group. Except for some nocturnal species, 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.

Primates are an extremely diverse group of between 190 and 350 living species, depending on different taxonomic structures, and exhibit a wide range of characteristic features that help distinguish them from other mammals. They range in size from the 2-ounce pygmy mouse lemur to the 440-pound wild gorilla. Humans share many traits with the other primates in the group.