1. ^*Department of Geology, Field Museum, Roosevelt Road at Lake Shore Drive, Chicago, Illinois 60605, USA
2. ^†Department of Geological Sciences, University of California, Santa Barbara, California 93106, USA
3. ^‡Departamento de Geología, Facultad de Ciencias Fisicas y Matematicàs, Universidad de Chile, Casilla 13518, Correo 21, Santiago, Chile
4. ^§Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, California 94709, USA

Abstract

PARTLY because of their poor fossil record, the relationships of neotropical platyrrhine monkeys to other groups of primates and to each other remain perhaps the most poorly known for any major primate clade¹. Here we report the discovery of a complete platyrrhine skull from the Andes of central Chile, by far the best preserved Tertiary primate cranium from South America. This find, coupled with recent phylogenetic analyses of higher groups of anthropoid primates^2–4, has the potential to revise substantially our understanding of platyrrhine interrelationships, indicating, among other points, significant modification to reconstruction of the ancestral platyrrhine morphotype and a likely African origin for New World monkeys. A ⁴⁰Ar/³⁹Ar radioisotopic date directly associated with the skull indicates an Early Miocene age⁵, marking the first report of South American mammals of this age from outside Argentine Patagonia. Finally, this discovery demonstrates the enormous potential of vastly distributed, but virtually untapped, Andean volcaniclastic deposits to yield further insights into the origin and diversification of South American primates.