An adaptive or evolutionary grade among the primates, represented by members of two of the three modern anthropoid superfamilies. The New World, platyrrhine monkeys (Ateloidea) and Old World, catarrhine forms (Cercopithecoidea) probably reached a monkey level of adaptation independently some time after their separation from a common ancestor, perhaps 45 million years ago (MYA; Fig. 1). The term monkey is not indicative of taxonomic or phylogenetic relationship: the closest relatives of the cercopithecoids are not the ateloid monkeys but the Old World apes and humans.  See also: Apes; Fossil apes; Fossil primates; Primates