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Evolution of Primates and of Mammalian Faunas in South America
For the past several years, I have been engaged in research in Argentina, Colombia, and Bolivia with three objectives:
1. to reconstruct the evolutionary history and adaptive patterns of South American primates and other mammals;
2. to establish a more precise geologic chronology for the mammalian faunas between the late Eocene and middle Miocene (between about 36 and about 15 million years ago); and
3. to use anatomy and niche structure of modern mammals as a means to reconstruct the evolution of mammalian niche structure in the Neotropics.
Primate Anatomy -- Implications for Phylogeny and Adaptations
A major theme of my work is to improve our understanding of two related topics:
1. the phylogeny of primates based (principally) on anatomical evidence; and
2. inferring the adaptations of extinct primates based mainly on cranial and dental evidence.
Plans for Future Research
Plans for research over the next 3-5 years are embodied in three projects. One is a particularly important site called the Gran Barranca in Patagonian Argentina that spans the Eocene-Oligocene transition, a period of particularly significant climatic change. A second project concentrates more particularly on recovery of early SA primate fossils at several localities of Early Miocene age (~17 Million years ago) in Argentine Patagonia. Finally, a project with Blythe Williams (principal investigator) is beginning in western India to search for continental vertebrates (especially primates) from the Paleocene through the Miocene.
Tracing Climate Change in the Eocene-Oligicene interval
This research is a study terrestrial biotic change in Patagonia through the Eocene-Oligocene transition (EOT). The end of the Eocene and the beginning of the Oligocene mark an important change in world climate from latitudinally more uniform, warmer, and more equable conditions to climates characterized by more latitudinal variation, cooler temperatures and more seasonality, i.e., when world climate transitioned from 'greenhouse' to 'icehouse'. The causes of this change are complex but involved regional tectonic activity as well as reorganized oceanic circulation. The timing and biotic impact of the change has been studied in the continental records of North America, Europe and Asia and shows a response to both local and global influences. As yet, however, no sequence of continental mammals and plants for the Eocene-Oligocene transition has been studied in the Southern Hemisphere. Recent revision of the ages of rock units and biotas in Patagonia has demonstrated that the Sarmiento Fm at Gran Barranca at 45° South in Patagonian Argentina spans the late Eocene through early Oligocene interval. In fact, this is the only known continental vertebrate and plant sequence so far identified from the Southern Hemisphere that spans this interval. The formation contains an as-yet inadequately sampled, but certainly rich, sequence of mammalian faunas and plant microfossils. Preliminary analysis of the mammalian herbivores suggests that dramatic changes occurred over a comparatively short interval of geologic time. The same sedimentary interval contains plant microfossils that document important change in the plant communities. Pilot data from mammalian tooth enamel suggest that these events occurred within the context of increasingly arid and more seasonal environments. The precise timing and nature of this biotic change, and its relation to the marine and Northern Hemisphere changes, will remain obscure until more fossils are collected in a more highly resolved temporal framework.
In this collaborative research undertaking, the geochronology of the Sarmiento Fm at Gran Barranca will be further refined using radiometric dating, chemical identification of tephra, and paleomagnetism. Stratigraphically-controlled collections will be made of vertebrates and plant microfossils. Climate change and its impact on the biota will be assessed 1) using biogeochemical analysis of stable oxygen isotopes in fossil mammalian tooth enamel; 2) by documenting changes in mammalian community structure (richness, origination and extinction rates, and ecological morphology); and 3) by documenting changes in vegetation and floral composition from the study of phytoliths. These three independent lines of evidence in a refined geochronologic framework will then be compared with similar evidence from continental sequences in the Northern Hemisphere and oceanic climatic data to improve our understanding of the timing and character of climatic change in continental high latitudes during this temporal interval.
Paleontological Investigations to Recover Fossil Monkeys from the Middle Cenozoic of South America
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.
Exploration for middle Cenozoic primates, Kutch District, Gujarat, western India
This funded project led by Blythe Williams and in collaboration with scientists at Panjab University will undertake a reconnaissance of Cenozoic (especially late Oligocene and early Miocene) rocks of Kutch, Gujarat State. The scientific importance of such an undertaking is high for documenting the earlier (hominoid) stage of human evolution. The immediate ancestors of the living Asian monkeys and apes, macaques, gibbons, and orangutans had African origins and disbursed to Europe and the Middle East beginning about 18 million years ago. But the oldest hominoid remains in Indo-Pakistan are dated at about 12 Ma. The timing of the movement of hominoids into Indo-Pakistan, and the nature of the evolutionary radiation of early representatives of the modern groups is constrained by the extremely poor record of fossil mammal sites older than 12 million years in this region. Since there are records of these groups from Turkey going back to 16 million years it is reasonable to suppose that they could have reached India in the early Miocene. We propose to prospect early Miocene strata already known to be fossiliferous in hopes of recovering earlier fossil apes.
Excavation of an Underwater Cavern Containing Primates, Other Extinct Vertebrates and Archaeological Remains in Hispaniola
A multidisciplinary survey of the Padre Nuestro cavern, southeastern Dominican Republic is the goal of this research. The cavern is underwater, but its floor was dry at the time of emplacement of extinct vertebrates and archaeological materials. Primates, rodents and sloths originated in South America and had arrived in the Antilles by the early Miocene, but absence of other typical Miocene South American taxa like carnivorous marsupials, armadillos, and notoungulates suggests that a connection between the continent and the islands were intermittent and subject to biotic or cross-water filters. Padre Nuestro contains thousands of loose bones on its floor that so far include many species of native cavioid rodents and several kinds of ground sloths. A skull of an Antillean primate has already been recovered and conserved. A particular emphasis will be the reassessment of the phylogenetic patterns of the primates and sloths using the new material because this contributes important information to the debate over the biogeographic origins of the Antillean fauna: did vertebrates arrive by a filter or via long-distance over-water sweepstakes dispersal and were there a single or multiple dispersal events? In addition, the cavern contains archaeological material that will improve knowledge of the timing and causes of extinction of sloths and primates in Hispaniola, in particular whether extinction was caused by climate change or was induced by the arrival of humans. If the archaeological remains can be shown to be autochthonous and undisturbed since the time of cave flooding, they represent an unusual insight about the culture of some of the earliest immigrants to the Antilles. The improved phylogenetic analyses made possible by the recovery of more complete remains of primates and sloths will allow tests of hypotheses regarding how and when these mammals entered the Greater Antilles. Geochemical analyses will provide the first direct evidence about the local environmental conditions under which these vertebrates lived. The research also contributes significantly to the Museo del Hombre Dominican and assists in training of staff in the conservation of bone preserved under these circumstances. The research is part of the effort to strengthen the fragile status of archaeological and paleontological remains and provide further support for stronger protection measures of this and similar sites.
Coastal exposures of the Santa Cruz Formation in southern Patagonia have been a fertile ground for recovery of Early Miocene vertebrates for more than 100 years: studies began in the 1840s when specimens were sent for study to Charles Darwin. The formation is noted for yielding remarkably complete specimens, and a richly varied taxonomic assemblage very different from other continents, due to the long isolation of South America. This volume presents the most comprehensive compilation of important mammalian groups which continue to thrive today. It includes the most recent fossil finds as well as important new interpretations based on 10 years of fieldwork by the authors. A key focus is place on the paleoclimate and paleoenvironment during the time of deposition in the Middle Miocene Climatic Optimum (MMCO) between 20 and 15 million years ago - a transient warming event similar to our current climate. Using newly recovered pollen, phytoliths and plant macrofossils together with invertebrates, amphibians and reptiles, the authors present the first reconstruction of what climactic conditions were like for this most southerly continental record of the MMCO. They also present important new evidence of the geochronological age, habits and community structures of fossil bird and mammal species. Academic researchers and graduate students in paleontology, paleobiology, paleoecology, stratigraphy, climatology and geochronology will all find this a valuable resource of information about this fascinating geological formation.