Doctoral Dissertation Improvement: Paleoecological Modeling and the Evolution of Early Eocene Primates in the Bighorn Basin, WY

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This study is proposed to advance the current understanding of the origin and evolution of the earliest primates. A broad-based, multidisciplinary approach will be used to analyze one of the most complete sequences of early fossil primates known. Though important contributions will also be made to the sciences of paleontology and paleoecology (the study of the interactions of ancient ecosystems), the main goal of this project is to relate primate evolution to environmental and community changes. The Willwood Formation of the Bighorn Basin, Wyoming, contains an extraordinary record of the history of early modern mammals. Deposited between 55 and 52.5 million years ago, it is one of the richest and most continuous early Eocene sequences in the world. Primates formed a significant and diverse element of the fauna preserved in the Willwood Formation, accounting for 10-20% of the individuals from many Willwood assemblages. Most of the fossil localities from the southern part of the Bighorn Basin have been tied into a composite sedimentary section of nearly 700m in thickness that is exposed over an area of more than 3000 km2.Intense fossil collecting efforts have been focused in the southern Bighorn Basin since the early 1960s, resulting in an enormous collection of fossils conservatively estimated to include as many as 100,000 vertebrate specimens. Recently, paleoenvironmental studies of the Bighorn Basin have incorporated innovations in stable isotope analysis to characterize the climate and depositional environment of these sediments. These new data are in excellent accord with previous paleoenvironmental reconstructions based on fossil soils and plant leaf physiognomy. With the emergence of these exciting and varied lines of evidence, it is now possible to examine the evolution of the Willwood primates in a tightly constrained time frame and in the context of a changing, regional environment.Studies of this type, grouped loosely under the heading 'paleoecology', have been critical in shaping hypotheses of primate and hominid evolution. The proposed project aims to accomplish a paleoecological analysis of the southern Bighorn Basin mammal community in two stages. The first is to quantify, using a random-sampling procedure, the pattern of faunal evolution during the first 2.5 million years of the Eocene in the southern Bighorn Basin. Preliminary analysis suggests that there have been episodes of concentrated faunal change (turnover). In the second stage, the resultant pattern will be tested for correspondence with the predictions of eight different current hypotheses of ecological models for evolutionary change. The results of this study will have important implications for scenarios of the evolution of the earliest primates and current arguments surrounding the paleoecological modeling of ancient ecosystems.The broader impacts of this study will include a contribution to current debates surrounding the impact of climate change on modern mammalian ecosystems. The results will illustrate the behavior and evolution of an ancient ecosystem in the face of changing regional temperature and moisture regimes, and shifting geological environments. In addition, the broader impacts include the graduate training of the Co-PI. The data collected will be useful in further research and will advance the scientific career of the Co-PI.