New World Monkeys

Abstract

Abstract New World monkeys are the nonhuman primates of South and Central America. Because almost all of their evolutionary history took place on the island continent of South America without competition from other primates, and most likely in a strictly arboreal setting, the character of their adaptation is unique. Fossils and molecules indicate the major lineages are long enduring, having attained diverse, stable ecological conditions quite early. Today, platyrrhine (wide‐nosed) monkeys comprise the most diversified taxonomic group among anthropoids. More primitive anatomically than Old World monkeys or apes, some forms resemble early fossil anthropoids from Egypt and serve well as models for reconstructing their behaviour. Others are more like the specialised apes in their locomotor adaptations, or the modified, folivorous leaf monkeys, whereas some evoke the big‐brained, extractive foraging strategies of African apes. Highly varied in their outward appearance as well, the range of social behaviours and mating strategies exhibited by platyrrhines is without equal among the primates. Key Concepts: New World monkeys occupy a wide variety of arboreal niches in the seasonally flooded forests of the Amazon and Orinoco river systems in continental South America, as well as more peripheral and less tropical biomes in southern South America, Central America and the Caribbean. Living New World monkeys are the smallest anthropoid primates, ranging across a span from less than 1 kg to approximately 10 kg. As an isolated, highly diversified radiation they are important models for studying parallel evolution in anatomy and behaviour while also providing living analogies for reconstructing the adaptations of extinct primates. The adaptive radiation of platyrrhines unfolded along cladistic lines, with each of the four main lineages occupying a distinct ecological zone characterised by a combination of body size, feeding preference and locomotor habit. The four main branches of the platyrrhine radiation, and some of the living genera, are older than any of the lineages or genera of Old World monkeys or apes. Where platyrrhines originally came from, directly from Africa or via North America, remains a difficult question as both hypotheses have their own pros and cons. The modern radiation of New World monkeys is an Amazonian phenomenon that was taking root 11–13 million years ago, as shown by fossils from a rich site in Colombia, but older, more primitive forms are found in Patagonia. Because of their dependence on multi‐level tropical forest ecosystems, New World monkey species are under acute threat of extinction as humans occupy and consume more and more forested areas and resources.