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Dental Ecometrics As a Proxy of Paleoenvironment Reconstruction in the Miocene Of Dental Ecometrics as a Proxy of Paleoenvironment Reconstruction in the Miocene of South America by Jackson Ples Spradley Department of Evolutionary Anthropology Duke University Date:_______________________ Approved: ___________________________ Richard F. Kay, Supervisor ___________________________ Blythe A. Williams ___________________________ James D. Pampush ___________________________ V. Louise Roth ___________________________ Doug M. Boyer Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Evolutionary Anthropology in the Graduate School of Duke University 2017 ABSTRACT Dental Ecometrics as a Proxy of Paleoenvironment Reconstruction in the Miocene of South America by Jackson Ples Spradley Department of Evolutionary Anthropology Duke University Date:_______________________ Approved: ___________________________ Richard F. Kay, Supervisor ___________________________ Blythe A. Williams ___________________________ James D. Pampush ___________________________ V. Louise Roth ___________________________ Doug M. Boyer An abstract of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Evolutionary Anthropology in the Graduate School of Duke University 2017 Copyright by Jackson Ples Spradley 2017 Abstract In this dissertation I compile modern mammalian faunal lists, as well as ecomorphological measurements on living marsupials and rodents, to relate the diversity of small mammals, specifically the distributions of their dental topographies, to the climates in which they are found. The emphasis of this dissertation is to demonstrate the potential of distributions of dental topography metrics as proxies for the reconstruction of paleoenvironments in the Miocene of South America. In Chapter 2, I compile complete, non-volant mammalian species lists for 85 localities across South America as well as 17 localities across Australia and New Guinea. Climatic and habitat variables were also recorded at each locality using GIS spatial data. Additionally, basic ecological data was collected for each species, including: diet, body size, and mode of locomotion. Niche indices that describe the relative numbers of different ecologies were calculated for each locality. These indices then served as the predictor values in a handful of regression models, including regression trees, random forests, and Gaussian process regression. The Australian/New Guinean localities were used as a geographically and phylogenetically independent for the purposes of testing the models derived from South America. As for the dental ecomorphological analysis, I use three separate measures of dental topography, each of which measures a different component of dental topography; relief (the Relief Index, or RFI), complexity (orientation patch count rotated, OPCR), and iv sharpness (Dirichlet normal energy, DNE). Together, these metrics quantify the shape of the tooth surface without regard for tooth size. They also do not depend on homologous features on the tooth surface for comparative analysis, allowing a broad taxonomic sample as I present here. After a methodological study of DNE in Chapter 3, I present correlative studies of dental topography and dietary ecology in marsupials and rodents in Chapters 4 and 5, respectively. Finally, using the same localities from Chapter 2, I analyze the distributions of dental topography metrics as they relate to climate and habitat. Results suggest that sharpness and relief are positively correlated with a higher amount of tough foods—such as leaves or insects—in the diet of marsupials, and that relief is positively correlated with grass-eating in rodents. The distributions of all three metrics show some utility when used as a proxy for climatic variables, though the distributions of RFI in marsupials and OPCR in rodents demonstrate the best correlations. Overall, this dissertation suggests that dental topography can be used to discriminate dietary categories in a wide variety of mammalian groups, and that the distributions of dental ecometrics can be used as proxies for paleoenvironment reconstruction. This may eliminate the need to reconstruct behavior in individual taxa in order to construct ecological indices for fossil mammalian communities, thus offering a more direct avenue to reconstructing past environments. v Dedication “Nature never did betray the heart that loved her.” -William Wordsworth To my mother and father, Patti and Ples Spradley, for their passing on to me the joy of understanding, and encouraging in me a love and appreciation of the Natural World. “You give but little when you give of your possessions. It is when you give of yourself that you truly give.” -Khalil Gibran To my wife, Sara, for her unceasing love, support, and companionship during this journey of intellectual and personal growth. Table of Contents Abstract ......................................................................................................................................... iv List of Tables ...............................................................................................................................xiv List of Figures ........................................................................................................................... xvii Acknowledgements ................................................................................................................... xxi 1. Introduction ............................................................................................................................... 1 1.1 Historical Context ............................................................................................................. 2 1.2 Modern Methods .............................................................................................................. 2 1.3 Dental Topography Metrics ............................................................................................ 8 1.4 Ecometrics of Small Mammal Cheek Teeth ................................................................ 12 1.5 Vagaries of the Fossil Record ........................................................................................ 14 1.6 Outline of Chapters ........................................................................................................ 17 2. Past Life Regression: Mammalian Faunas, Ecological Indices, and Machine-Learning Regression for the Purpose of Paleoenvironment Reconstruction in the Miocene of South America ........................................................................................................................................ 21 2.1 Background ..................................................................................................................... 23 2.1.1 Regression Methods of Paleoecological Reconstruction ...................................... 28 2.1.1.1 Multivariate Linear Regression ........................................................................ 28 2.1.1.2 Regression Tree Analysis .................................................................................. 29 2.1.1.3 Random Forests .................................................................................................. 31 2.1.1.4 Gaussian Process Regression ............................................................................ 35 2.1.2 Paleoecological Reconstruction ............................................................................... 36 vii 2.1.2.1 La Venta Paleogeography ................................................................................. 37 2.1.2.2 Santa Cruz Paleogeography ............................................................................. 38 2.2 Materials and Methods .................................................................................................. 40 2.3 Results .............................................................................................................................. 47 2.3.1 Spatial Autocorrelation ............................................................................................. 47 2.3.2 South American extant faunas ................................................................................. 47 2.3.3 Australian extant faunas........................................................................................... 56 2.3.3 Paleoclimatic Reconstructions ................................................................................. 60 2.3.3.1 The Monkey Beds of La Venta ......................................................................... 60 2.3.3.2 Santa Cruz Faunal Levels 1-7 ........................................................................... 61 2.4 Discussion ........................................................................................................................ 62 2.4.1 Performance of regression techniques in South American data ......................... 63 2.4.2 Results from modern localities ................................................................................ 65 2.4.2.1 Mean annual precipitation (MAP) ................................................................... 65 2.4.2.2 Mean annual temperature (MAT) ................................................................... 66 2.4.2.3 Temperature seasonality ................................................................................... 67 2.4.2.4 Precipitation seasonality ..................................................................................
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