Platyrrhine Ecophylogenetics in Space and Time

Abstract

New World Monkeys (NWM) evolved not in a monolithic South America, but within and around at least four now distinct regions, the Amazonian, Atlantic, Patagonian and Caribbean provinces. Large-scale features of the continent, including its geometry, tectonics and proximity to Antarctica have been important in shaping platyrrhine evolution. While the insular Caribbean is difficult to characterize, only the Amazonian environment, which covers roughly 40% of the continent, is the stereotypically warm, wet, lush, physically complex, three-tiered rainforest habitat, with ultra-high biotic productivity, biodiversity and endemism. Driven by Andean uplift, the evolution of Amazonian physiography may have begun only 15 million years ago (Ma), to become modern in structure about 3 Ma, whereas primates arrived in South America more than 26 Ma. Paleontology and biogeography suggest that today’s Amazonian primates, despite great endemism, are a composite fauna involving forms that may have emerged outside the basin, in less rich, less productive, semi-deciduous environments resembling the Atlantic province and even more marginal habitats. Possible genera of extra-Amazonian origin include Alouatta, Cebus, Callicebus and Aotus; native genera may include Ateles, Chiropotes and Cacajao. The fossil primates from La Venta, Colombia, and the younger ones from Acre, Brazil, are frequently modern and Amazonian in character, indicating the province has been ecophylogenetically and geographically coherent for at least 12-14 Ma. Fossils and subfossils of the Caribbean and the Quaternary of Brazil have a primitive, pre-Amazonian aspect. In the far south, over a five million year period, 15-20 Ma, there is little evidence of temporal continuity. That primate fauna is diminished, dominated by primitive, though ecologically adaptable pitheciines, and probably marked by high extinction rates. Adjacent to Antarctica, the development of polar ice sheets strongly influenced the Patagonian climate, promoting the evolution of an extensive grassland flora and fauna long before NWM arrived, probably limiting influx to those able to live in marginal conditions. Although most of habitable South America remains grassland, the low probability of terrestriality evolving among NWM is explicable in light of: the predominance of arboreality in the Order Primates; ecological conditions of the past 15 million years during which time the gigantic Amazonian province was composed of lakebed or immense riverbeds; selection for positional behaviors related to subcanopy resource exploitation, and are antithetical to preadaptations promoting a locomotor transition to the forest floor which was very likely flooded for long stretches of geological time.