Final answer:
Old World monkeys, found in Africa and Asia, have narrow, downward-facing nostrils and non-prehensile tails, with some species being ground-dwellers. New World monkeys, located in Central and South America, have broad noses, side-facing nostrils, and prehensile tails, with many species forming pair bonds and exhibiting little sexual dimorphism.
Step-by-step explanation:
Old World Monkeys vs. New World Monkeys
The primary differences between Old World monkeys and New World monkeys involve physical and behavioral characteristics that have evolved due to their geographical separation. The Old World monkeys belong to the infraorder Catarrhini and are mostly found in Africa and Asia. They have narrow, downward-facing nostrils, and their tail is not prehensile. Unlike New World monkeys, some Old World species are ground-dwelling in addition to being arboreal, and they often display sexual dimorphism with males typically being larger than females.
New World monkeys, belonging to the infraorder Platyrrhini, inhabit the tropical forests of Central and South America. They are recognizable by their broad noses with nostrils that open to the sides. These monkeys have a distinctive feature, a prehensile tail, which acts as an extra limb for better arboreal navigation. In terms of social behavior, many New World monkey species form pair bonds and tend to show little size difference between sexes.
The divergent evolutionary paths of the Old World and New World monkeys are a result of being in separate environments after their ancestors drifted apart amidst continental shifts. Additionally, Old World monkey groups include both cheek pouch monkeys and leaf-eating monkeys, while the New World groups consist of species like tamarins and marmosets. Reproductive isolation allowed these two groups to undergo distinctive adaptive radiations, developing unique adaptations to their respective environments.