The pattern of monkey evolution in South America is poorly documented and little understood. Some argue that New World monkeys (Platyrrhini) known from 16-20 million year old rocks of Patagonia predate the origins of the modern families, that is, they are 'stem platyrrhines'. Others argue that they are early representatives of the modern platyrrhine families. The two alternative interpretations have profound implications for how the evolutionary radiation of platyrrhines is viewed. Further fossil material of early platyrrhines will contribute to resolving this debate. A joint team of US and Argentine paleontologists will search for fossil primates in ~16 million-year-old rocks of the Santa Cruz Formation and its equivalents in Patagonian Argentina. Collecting will concentrate on proven localities and expand collecting efforts to other lesser-known sites said to be richly fossiliferous from the Atlantic coast inland to the Andean front at 50-55 degrees South latitude. Analysis of the existing materials and recovery of even more complete specimens of primates will offer a rare insight about the phylogeny and adaptations of these early anthropoid primates. A phylogenetic analysis will clarify the pattern of diversification of South American platyrrhine monkeys and help to refine hypotheses about the origins of the modern platyrrhines families. To reconstruct adaptive profile of the various extinct species, a team of scientists from the US, Argentina and Brazil will study various aspects of the teeth, skulls and limb bones to reconstruct important details of the each species' adaptation and life history. Collections of other faunal remains by the field group will fill out the environmental context in which early platyrrhines evolved. A second team of research specialists headed by the Argentine scientists will study the functional anatomy and ecomorphology of non-primate fossils. Much work already has been undertaken to study the sloths and armadillos. Using these established approaches as a model, the research group will extend this work to encompass other major mammal groups including rodents, notoungulates, and marsupials.
The research was conducted along the coast of Patagonian, Argentina, South America just 600 km from Antarctica by an international collaborative team of US and Argentinean scientists from disparate fields of paleoprimatology, stratigraphy, paleontology, paleobotany, and geochemistry. The fossil localities studied are world-famous for their 19 to 15 million year old (Miocene) fossil mammals, especially South American anthropoid primates, also called platyrrhines or New World monkeys. The sites contain the most complete fossil platyrrhines from their first known appearance on the continent at about 26 million years ago until the Holocene. The information that has been revealed by such complete fossils has given scientists unparalleled insights into early platyrrhine biology, ecology, and phylogeny. The scientific questions addressed in this research are of broad paleoanthropological and paleontological significance. First, the newly recovered fossils document more fully the evolution and adaptations of platyrrhines that make up a significant fraction of the modern biodiversity of tropical South America (17 genera and >130 species). Some argue that these Patagonian Miocene monkeys predate the origins of the modern families, that is, they are 'stem platyrrhines'. Others argue that they are early representatives of the modern families. The two alternative interpretations have profound implications for how the evolutionary radiation of platyrrhines is understood. Our recovery of new fossil skulls and limb-bones of monkeys adds support to the ‘stem’ platyrrhine hypothesis. A second question involves the response of mammals to climate change. The fossil sites offer added scientific information about the onset of a period of climate warming called the Mid-Miocene Climate Optimum (MMCO), which accounts for the occurrence of monkeys and other typically ‘tropical’, e. g., temperature sensitive, mammals, birds, reptiles and amphibians and even palm trees 20° of latitude south of their current distributional limits. An analysis was undertaken to evaluate of the responses of vertebrates to MMCO climate and has increased our understanding of the mammalian community structure and environments of the Miocene at far-southern latitudes. The broader impact of this research was the field and laboratory training of students and professionals including three US graduate students and three Argentinean postgraduate students. As a result of the fieldwork we collected more than 4000 fossil vertebrate specimens that were deposited in the regional natural history museum in Santa Cruz Province, Argentina. Each year the lead scientists from both countries visited local public and private primary schools allowing students to handle, talk about, and understand the significance of fossils.
