These large monkeys belong to the New World family Atelidae which also contains the Woolly Monkeys & the Howler Monkeys. All the members of this family have the ability to support their entire weights by their gripping prehensile tails. There the similarity ends as Spider Monkeys are a much smarter primate than their dim-witted Howler Monkey cousins. Spider Monkeys have complex social structures & basic problem-solving abilities which is reflected in the fact that at 107 grams, the spider monkey brain is twice the size of a howler monkey's of equivalent body size!!!