Primates

Monkeys
Prosimians
Apes

Physical description

Living primates cover a very large range of body sizes.

There is accordingly a more than 5,000-fold difference between the smallest and largest living primates.

Among living primates, it is notable that nocturnal species are generally markedly smaller than diurnal species.

The hands and feet of primates are typically adapted for grasping rather than grappling while moving around.

A widely divergent big toe (hallux) provides the basis for a powerful grasping action of the foot in all primates except humans, while the hand usually exhibits at least some grasping capacity.

It is notable that nocturnal species are generally markedly smaller than diurnal species.

In most primates, the digits (fingers and toes) typically bear flat nails rather than narrow claws, and in all cases the hallux bears a nail.

On the ventral surfaces of the hands and feet there are tactile pads with skin ridges (dermatoglyphs) that serve an anti-slip function on twigs and branches.

Patterns of movement are typically hindlimb-dominated.

The location of the body's center of gravity is typically closer to the hind limbs, with the result that the typical walking style shows a diagonal sequence.

In the foot, there is usually at least some degree of relative drawing out of the distal segment of the heel bone.

Primates also tend to have longer limbs, in relation to overall body size, than other mammals, and this results in increased stride length.

The visual sense is greatly emphasized in primates.

Primates are unique among living mammals in that the brain constitutes a significantly larger proportion of body weight at all stages of fetal development.

The dental formula exhibits a maximum of two incisors, one canine, three premolars and three molars on each side of upper and lower jaws.

The difference from ancestral mammals in the loss of one incisor and one premolar from each toothrow.

In association with the reduction in the number of incisors, the premaxilla bone at the front of the upper jaw is very short, and the incisors are arranged more across than the other side.

The cheek teeth are typically relatively unspecialized, although the cusps are generally low and rounded, while in the lower molars the heels (tabloids) are raised and enlarged.

Behavior

Primates generally live in well-developed social networks and this can be regarded as a defining characteristic of the order.

Although species that are active by night (nocturnal) have commonly been described as solitary, field studies have revealed that there are intimate social links between individuals, maintained by intermittent contacts during the night and by sharing of nests during the daytime.

Nevertheless, there is a major distinction between day-active (diurnal) primates and nocturnal species in that the former typically live in obvious cohesive social groups, whereas the latter usually move around and feed alone at night.

In sum, while all primates have intricate social systems, as a general rule diurnal species are gregarious whereas in nocturnal species individuals are dispersed.

Among nocturnal primates, the only exceptions to solitary behavior are found in a few species that are monogamous (pair living), such as the avahis (Avahi) in Madagascar and the owl monkeys in the New World.

Among diurnal primates, the only representative that is almost solitary like most nocturnal primates is the orangutan of Southeast Asia.

	The groups of social diurnal primates can be classified into three main categories according to the composition of their groups
	Monogamous
	Family units
	One-male groups and multi-male groups.

	Monogamous (married) groups typically consist of an adult pair living together with their immature offspring.
	Clear-cut examples of monogamy are found among lemur’s avahis, mongoose lemurs, red-bellied lemurs, and indri,

	New World monkeys
	Owl monkeys
	Marmosets
	Tamarins
	Goeldi's monkey
	Capuchins
	Howler monkeys
	Spider monkeys
	Woolly monkeys
	Old World monkeys
	Mentawai langur
	Gibbons.
	Plains baboons,
	Vervet monkeys,
	Red Colobus

	One male group
	Hamadryas baboons
	Geladas
	Guenons
	Patas monkeys
	Black-and-white Colobus
	Several langur species
	Gorillas
	Several harem groups
	Hamadryas baboons
	Geladas.

	Social groups
	Ringtails Lemur
	Sifaka
	Chimpanzees.

One very common form of social interaction is grooming, which is frequently reciprocal.

Even in nocturnal primate species that show dispersal of individuals at night, and in orangutans, which are usually dispersed by day.

Social grooming is a prominent feature of occasional encounters between familiar individuals.

	Prosimians
	Social grooming is usually carried out mainly with the teeth.

Lemurs and Lorises the toothcomb is actively used called (strepsirrhines).

Nocturnal lemurs and Lorises still have relatively large olfactory bulbs in the brain, and marking with urine or feces and with secretions from special skin glands on the chest is prominent.

In higher primates, by contrast, the hands usually play a more intense role in social grooming, particularly in Old World monkeys and apes.

For dispersed nocturnal Prosimians, olfactory marking may be the primary means of communication between individuals while active.

Visual displays are particularly important in diurnal primates.

Some of which have developed quite striking coloration patterns of the fur certain lemurs, Old World monkeys, and gibbons.

In fact, ring-tailed lemurs show an interesting display pattern that combines both olfactory and visual elements.

During encounters between groups that have been labeled stink fights, individuals anoint their tails with secretions from marking glands on the arms and then wave their tails in the air while strutting around.

Perhaps the greatest diversity of color patterns on the face and elsewhere on the body is found in the African guenons, which often have characteristic head movements that emphasize any species-specific facial markings.

Vocalizations are also generally important for social interactions among primates.

Nocturnal primates usually have a relatively restricted vocal repertoire, but the calls that they do have are important for maintaining contact between dispersed individuals.

Diurnal primates generally have richer vocal repertoires containing numerous calls in the audible range and their subtlety can be quite pronounced, particularly in certain Old World monkeys and chimpanzees.

Many species like the lion Tamarins have long calls to maintain contact between neighboring groups.

Although it is often assumed that all primates show territorial behavior, defense of an exclusive territory is in fact comparatively rare among primates.

Numerous nocturnal primates show range overlap between adults of both sexes, and diurnal primates that live in gregarious groups often show quite extensive overlap between group ranges.

Some nocturnal Prosimians, such as sportive lemurs in Madagascar and in a minority of diurnal primates, including some lemurs, show true territoriality in the sense of behavior shown to defend an exclusive area.

There seems to be a general trend for primates that live in monogamous groups to show marked territorial behavior, and it has in fact been suggested that one of the factors promoting monogamy is joint defense of an area containing vital resources.

Territorial behavior has been found in a variety of monogamous species, including such nocturnal lemurs as avahis, such cathemeral lemurs as the mongoose lemur, such diurnal lemurs as the indri, most marmosets and Tamarins, and all gibbons

In fact, the indri, the gibbons, lion Tamarins, and titi monkeys show conspicuous, often melodious vocalizations that carry over great distances in the forest and seem to play a part in territoriality.

These "great calls" of the monogamous indri and gibbons provide one of the most striking examples of convergent evolution to be found among primates.

	Most primate species are either exclusively nocturnal (active at night between morning and evening) or clearly diurnal (active by day between morning and evening).
	The majority of Prosimians primates are nocturnal in habits, whereas simian primates are typically diurnal.
	Indeed, the only nocturnal representatives among simian primates are the owl monkeys of South and Central America and all the rest of the monkeys and apes, like humans, are diurnal.
	Natural groups of Prosimians primates
	Nocturnal species
	Loris
	Tarsiers
	Lemurs

These species contains mainly nocturnal species but also some diurnal species. Lemurs, there is also an unusual pattern known as cathemerality in which there is a combination of nocturnal and diurnal activity.

Compared to other mammals, all primates have relatively large eyes, but in nocturnal primates the eyes are generally even larger.

Feeding Habits

Primate species exhibit a wide range of diets, although most of them include at least some fruits in their food intake.

If there is a typical dietary category for primates generally, it is surely fruit consumption, as this is found from the smallest to the largest species.

Although most primates eat at least some fruits, primates can be classified into three main dietary categories representing at least 50% of food intake:

	Insectivores, feeding mainly on arthropods (tarsiers)
	(2) Frugivores, feeding mainly on fruits (e.g., most forest-living monkeys).
	(3) Folivores, feeding mainly on leaves (leaf-monkeys).
	There is a general trend among primates for the diet to shift progressively from insectivore through frugivory to folivory as body size increases.

This is understandable because small-bodied mammals have relatively high-energy requirements per unit body weight and must eat foods with rich, easily available energy content.

Large-bodied mammals have relatively low energy requirements per unit body weight and can consume foods that have a poor energy content and require extensive digestion.

As a general rule, insectivorous primates do not exceed 1.5 lb (700 g) in body weight, while folivorous primates tend to be quite large-bodied species.

In fact, a fourth dietary category known as gummivory must be recognized for primates whose food intake includes more than 50% of plant exudates (gums).

Gums resemble fruits in that they are a major source of carbohydrates.

But they resemble leaves in that the carbohydrates are polymerized and require extensive digestion.

Many primate species include at least some plant exudates in their diets,

Gum-Feeding Specialists

	Fork-crowned lemur
	Needle-clawed bush baby
	Marmosets