ordinal name primates, means the first or primary animals. This
naming convention reflects the egocentric orientation of humans,
but is of no help in defining the group of mammals included
in it. Primates are mainly arboral mammals, but terrestrial
forms occur in several groups. Most primates are omnivorous.
Several groups are almost entirely herbivorous. The galagos
and tasrsiers are largely insectivorous. Most primates are pentadactyl,
although some fingers are shorter in some Lorises. The thumb
is reduced in several brachiating forms and completely absent
in spider monkeys. In most primates the digits are prehensile
and the pollex and/or the hallux are more or less opposable.
These prehensile and apposable digits yield a hand or foot with
great dexterity, allowing the animal to better grasp and manipulate
objects. In general the sense of smell in primates becomes less
acute as the hand becomes better adapted for manipulation. Primates
have developed very good vision, particularly those that are
diurnal. The field of vision of the two eyes overlap considerably,
resulting in more precise depth perception. The retina of some
nocturnal primates is composed entirely of rods. The eyes are
directed more or less frontally, and the face is foreshortened
in many forms. Only humans are completely bipedal.
single species, Homo sapiens, is nearly worldwide in
distribution. Otherwise other members of the order are found
in the Americas from eastern and southern Mexico to southeastern
Brazil, most of Africa, Madagascar, the southwestern part of
the Arabian Peninsula, south-central and southeastern Asia,
Japan and the East Indies as far as Sulawesi and Timor.
includes 13 Families, 71 genera and 233 species within the Order
Primates. Since humans are themselves primates, the order has
attracted much interest and investigation, and there are numerous
views on classification, especially between the order and family
levels. Simpson's (1945) scheme is followed by Walker.