are an ancient and diverse eutherian group, with around 233 living
species placed in 13 families. Most dwell in tropical forests. The
smallest living primate is the pygmy mouse lemur, which weighs around
30 g. The largest is the gorilla, weighing up to around 175 kg.
Primates radiated in arboreal habitats, and many of the characteristics
by which we recognize them today (shortened rostrum and forwardly
directed orbits, associated with stereoscopic vision; relatively
large braincase; opposable hallux and pollex; unfused and highly
mobile radius and ulna in the forelimb and tibia and fibula in the
hind) probably arose as adaptations for life in the trees or are
primitive traits that were retained for the same reason. Several
species, including our own, have left the trees for life on the
ground; nevertheless, we retain many of these features.
usually recognized based on a suite of primitive characteristics
of the skull, teeth, and limbs. Some of these are listed above,
including the separate and well-developed radius and ulna in the
forearm and tibia and fibula in the hindleg. Others include pentadactyl
feet and presence of a clavicle. Additional characteristics (not
necessarily unique to primates) include first toe with a nail, while
other digits bear either nails or claws, and stomach simple in most
forms (sacculated in some leaf-eating cercopithecids). Within primates,
there is a tendency towards reduction of the olfactory region of
the brain and expansion of the cerebrum (especially the cerebral
cortex), correlated with an increasing reliance on sight and increasingly
complex social behavior.
The teeth of
primates vary considerably. The dental formula for the order is
0-2/1-2, 0-1/0-1, 2-4/2-4, 2-3/2-3 = 18-36. The incisors are especially
variable. In some forms, most incisors have been lost, although
all retain at least 1 lower incisor. In others, the incisors are
intermediate in size and appear to function as pincers or nippers,
as they commonly do in other groups of mammals. In some, including
most strepsirhines (see next paragraph), the lower incisors form
a toothcomb used in grooming and perhaps foraging. In the aye-aye
(Daubentoniidae), the incisors are reduced to 1 in each jaw and
are rodent-like in form and function. Canines are usually (but not
always) present; they vary in size, including within species between
males and females. Premolars are usually bicuspid (bilophodont),
but sometimes canine-like or molar-like. Molars have 3-5 cusps,
commonly 4. A hypocone was added early in primate history, and the
paraconid was lost, leaving both upper and lower teeth with a basically
quadrate pattern. Primitively, primate molars were brachydont and
tuberculosectorial, but they have become bunodont and quadrate in
a number of modern forms.
are divided into two great groups, the Strepsirhini and the Haplorhini.
Strepsirhines have naked noses, lower incisors forming a toothcomb,
and no plate separating orbit from temporal fossa. The second digit
on the hind foot of many strepsirhines is modified to form a "toilet
claw" used in grooming. Strepsirhines include mostly arboreal
species with many primitive characteristics, but at the same time,
some extreme specializations for particular modes of life. Haplorhines
are the so-called "higher" primates, an anthropocentric
designation if ever there was one. They have furry noses and a plate
separating orbit from temporal fossa, and they lack a toothcomb.
Haplorhines include many more species, are more widely distributed,
and in most areas play a more important ecological role. Haplorhines
are further divided into two major groups, the Platyrrhini and the
Catarrhini. Platyrrhines have flat noses, outwardly directed nasal
openings, 3 premolars in upper and lower jaws, anterior upper molars
with 3 or 4 major cusps, and are found only in the New World (families
Cebidae and Callitrichidae). Catarrhines have paired downwardly
directed nasal openings, which are close together; usually 2 premolars
in each jaw, anterior upper molars with 4 cusps, and are found only
in the Old World (Cercopithecidae, Hylobatidae, Hominidae).
species live in the tropics or subtropics, although a few, most
notably humans, also inhabit temperate regions. Except for a few
terrestrial species, primates are arboreal. Some species eat leaves
or fruit; others are insectivorous or carnivorous.
Here, we follow
Anderson and Jones (1984) in formally dividing living primates into
two suborders, the Strepsirhini and the Haplorhini. We differ, however,
in that we place humans and their close relatives, the chimpanzee,
gorilla, and orang in the family Hominidae.