New World monkeys are the five families of primates that are found in Central and South America and portions of Mexico: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Platyrrhini parvorder and the Ceboidea superfamily, which are essentially synonymous since Ceboidea is the only living platyrrhine superfamily. Platyrhini means flat-nosed, and their noses are flatter than those of other simians, with sideways-facing nostrils. Monkeys in the family Atelidae, such as the spider monkey, are the only primates to have prehensile tails. New World monkeys' closest relatives are the other simians, the Catarrhini ("down-nosed," comprising Old World monkeys and apes). New World monkeys descend from African simians that colonized South America, a line that split off about 40 million years ago.