Primate - Distinguishing Features

Distinguishing Features

Primates have diversified in arboreal habitats (trees and bushes) and possess many characteristics that are adaptations to this environment. They are distinguished by:

• retention of the collar bone in the pectoral girdle;
• shoulder joints which allow high degrees of movement in all directions;
• five digits on the fore and hind limbs with opposable thumbs and big toes;
• nails on the fingers and toes (in most species);
• a flat nail on the hallux (in all extant species);
• sensitive tactile pads on the ends of the digits;
• orbits encircled in bone;
• a trend towards a reduced snout and flattened face, attributed to a reliance on vision at the expense of olfaction (most notably in haplorrhines, and less so in strepsirrhines);
• a complex visual system with stereoscopic vision, high visual acuity and color vision;
• a brain having a well-developed cerebellum with posterior lobe and a calcarine fissure;
• a large brain in comparison to body size, especially in simians;
• differentiation of an enlarged cerebral cortex;
• reduced number of teeth compared to primitive mammals;
• three kinds of teeth;
• a well-developed cecum;
• two pectoral mammary glands;
• typically one young per pregnancy;
• a pendulous penis and scrotal testes;
• long gestational and developmental periods; and
• a trend towards holding the torso upright leading to bipedalism.

Not all primates exhibit these anatomical traits, nor is every trait unique to primates. For example, other mammals have collar bones, three kinds of teeth and a pendulous penis, while spider monkeys have greatly reduced thumbs, ruffed lemurs have six mammary glands and strepsirrhines generally have longer snouts and a strong sense of smell.

In regard to behavior, primates are frequently highly social, with flexible dominance hierarchies. New World species form monogamous pair bonds, and show substantial paternal care of their young, unlike most Old World monkeys.