Final answer:
Old World monkeys reached South America either by drifting on log rafts or by crossing land bridges when the continents were still connected. This led to separate evolutionary developments for New World and Old World monkeys. New World monkeys are arboreal with prehensile tails, while Old World monkeys include both arboreal and ground-dwelling species with non-prehensile tails.
Step-by-step explanation:
Old World monkeys are believed to have reached South America either by drifting on log rafts or by crossing land bridges when the continents of South America and Africa were still connected. This reproductive isolation caused Old World monkeys and New World monkeys to undergo separate adaptive radiations over millions of years. New World monkeys are arboreal and have prehensile tails, while Old World monkeys include both arboreal and ground-dwelling species and have non-prehensile tails. Some established populations of introduced primates have also contributed to the presence of Old World monkeys in South America.