The modern primates are a diverse order of mammals that includes lemurs, lorises, tarsiers, monkeys, apes and humans. They are united by a 65 My evolutionary history originally built on an adaptive foundation of tropical arboreality and so they share a collection of traits that are unique among mammals, such as an excellent sense of balance, acute vision, good hand–eye coordination, a large grasping first toe, prehensile feet and hands and a flexible, athletic limb anatomy. Primates also tend to live in relatively large social groups and often have correlatively enlarged brains. They almost always give birth to singletons that grow over a prolonged period, which is advantageous to cognitive development, learning and socialisation. Fossil nonhuman primates have been found on all continents but Australia and Antarctica. Primates have been important elements of tropical and subtropical faunas since mammals rebounded following the mass extinction that also promoted the demise of dinosaurs.

Key Concepts:

• Primates are a highly diversified and successful order of mammals adapted to an arboreal, tropical lifestyle.
  
• There are three major surviving radiations – lemurs and lorises (strepsirhines) and Old World monkeys and apes (catarrhines) occur in Africa and Asia, and New World monkeys (platyrrhines) live in Central and South America – but many species are now threatened with extinction and the fourth radiation consists of only one genus, the tarsiers of eastern Asia.
  
• Although they arose from different ancestral stocks and display their own distinctive character, each radiation exhibits parallel evolution in dietary, locomotory and social adaptation to a treed environment, and all exhibit the universal primate characteristics of grasping big toes, some form of manual prehension and a preference for eating fruits – except for the exclusively predaceous tarsiers.
  
• Fossil primates are fairly well known and modern in appearance as early as the Eocene epoch, when many existing orders of mammals are also prevalent, but there is controversy as to where to set the primate–nonprimate boundary that influences how the older plesiadapiforms should be classified – in or outside of the primate order.
  
• The two largest primate clades, strepsirhines and haplorhines, one heavily reliant on the sense of smell and basically nocturnal and the other depending on vision and essentially diurnal, already existed approximately 55 Ma, but where and when anthropoids split from early haplorhines, and how the earliest members can be identified from limited sets of fossils, has not been determined.
  
• The New World platyrrhine monkeys are an early offshoot of anthropoids and only distantly related to Old World monkeys, a group that is more closely related to apes and humans.
  
• Increasing brain size as a correlate of increasing social group size is a pattern that evolved multiple times among anthropoids, irrespective of dietary preferences.
  
• The prolific early apes of the Miocene were eclipsed by the diversification of Old World monkeys in forested and open country habitats, especially in sub-Saharan Africa.