STABLE ISOTOPE PALEOECOLOGY OF AN EARLY MIOCENE EQUID (PARAHIPPUS LEONENSIS) FROM THE THOMAS FARM SITE, GILCHRIST COUNTY, FLORIDA By SEAN MICHAEL MORAN A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2014 © 2014 Sean Michael Moran To Mom, whose constant bravery and strength during her fight against cancer has been a constant source of inspiration ACKNOWLEDGMENTS First and foremost, I would like to thank my advisor, Bruce MacFadden, for providing superb guidance of the project along the way. He always pushed me to look at things in a different light when the data appeared utterly uninteresting. I also thank my committee, Jonathan Bloch and Andrea Dutton, who provided much needed, valuable input over the last couple of years. The Geological Society of America, National Science Foundation (CSBR 1203222, PIRE 0966884), University of Florida Department of Geological Sciences, and the Southwest Florida Fossil Club provided funding throughout the duration of this project and for that I am grateful. For those listed below, who provided assistance, whether lending an ear to listen to various ideas, providing useful suggestions, critiquing the final product, or assisting with sampling and sample selection: Elliot Arnold, Jason Bourque, Mark Brenner, Jason Curtis, Amanda Friend, Pam Haines, Richard Hulbert, Michal Kowalewski, Carly Manz, Ellen Martin, Candace McCaffery, Paul Morse, Irv Quitmyer, Dave Steadman, Chanika Symister, Julia Tejada, Lane Wallet, Evan Whiting, Aaron Wood, and my family. This is far from an inclusive list and I am truly appreciative for the many other people who have provided support. 4 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 7 LIST OF FIGURES .......................................................................................................... 8 LIST OF ABBREVIATIONS ............................................................................................. 9 ABSTRACT ................................................................................................................... 10 CHAPTER 1 INTRODUCTION .................................................................................................... 12 Background ............................................................................................................. 12 The Thomas Farm Site ........................................................................................... 13 An Important Miocene Equid ................................................................................... 15 Stable Isotopes ....................................................................................................... 16 A Review of δ13C .................................................................................................... 18 A Review of δ18O .................................................................................................... 19 Research Questions ............................................................................................... 20 2 MATERIALS AND METHODS ................................................................................ 24 Sample Selection .................................................................................................... 24 Isotope Sample Collection ...................................................................................... 25 Sample Pretreatment .............................................................................................. 25 Sample Analysis ..................................................................................................... 26 3 RESULTS ............................................................................................................... 28 δ13C: Corrections .................................................................................................... 28 δ18O: Conversions and Corrections ........................................................................ 28 δ13C: Results ........................................................................................................... 30 18 δ Ocarbonate: Results ................................................................................................ 31 18 δ Ow: Results ......................................................................................................... 32 Diagenesis .............................................................................................................. 33 4 DISCUSSION ......................................................................................................... 44 No Evidence for C4 Feeding in Parahippus leonensis ............................................. 44 Patterns of Weaning ............................................................................................... 45 Paleoclimatic Interpretations of Thomas Farm ........................................................ 48 No Evidence for Seasonality of Birthing in P. leonensis ......................................... 51 5 Mineralization Patterns ........................................................................................... 52 5 CONCLUSIONS ..................................................................................................... 55 APPENDIX A ISOTOPIC DATA .................................................................................................... 57 LIST OF REFERENCES ............................................................................................... 61 BIOGRAPHICAL SKETCH ............................................................................................ 70 6 LIST OF TABLES Table page 18 3-1 δ Ow (V-SMOW) estimates for the four known equations. ................................ 34 3-2 δ13C (V-PDB) data for each of the six sample locations ..................................... 34 18 3-3 δ Ocarbonate (V-PDB) data for each of the six sample locations .......................... 34 18 3-4 δ Ow (V-SMOW) data for each of the six sample locations ............................... 35 A-1 All isotope data collected from the study ............................................................ 58 7 LIST OF FIGURES Figure page 1-1 Map of Florida showing the location of the Thomas Farm locality and other data used in the study. ....................................................................................... 22 1-2 Diagram showing δ13C fractionation in vegetation and herbivores. All values given are in reference to V-PDB ......................................................................... 23 2-1 UF 258802 .......................................................................................................... 27 18 18 3-1 Plot showing the linear relationship between δ Ophosphate and δ Ow ................. 36 18 3-2 Box and whisker plot showing the variation in δ Ow estimates between equations 3-3 to 3-6 ............................................................................................ 37 18 13 3-3 Bivariate plot of estimates of δ Ow and δ C ...................................................... 38 3-4 Box and whisker plot of δ13C by sample location ................................................ 39 3-5 Plot of δ13C values of each sample position compared with a resampled distribution .......................................................................................................... 40 13 13 3-6 Plot of mean δ C against Δδ Capex-base. ............................................................ 41 13 3-7 Histogram showing the distribution of Δδ Capex-base values. ............................... 42 18 3-8 Box and whisker plot for estimated δ Ow values. .............................................. 43 4-1 Graph of δ18O values for north-central Florida. ................................................... 54 8 LIST OF ABBREVIATIONS E/P Ratio of evaporation to precipitation FGS Specimens collected by the Florida Geological Survey, now in collections of the Florida Museum of Natural History Vertebrate Paleontology division FLMNH Florida Museum of Natural History M1 Upper first molar m1 Lower first molar M2 Upper second molar m2 Lower second molar m3 Lower third molar p2 Lower second premolar UF Denotes specimens housed in the collections of the Florida Museum of Natural History at the University of Florida 9 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science STABLE ISOTOPE PALEOECOLOGY OF AN EARLY MIOCENE EQUID (PARAHIPPUS LEONENSIS) FROM THE THOMAS FARM SITE, GILCHRIST COUNTY, FLORIDA By Sean Michael Moran August 2014 Chair: Bruce MacFadden Major: Geology The importance of the early Miocene equid, Parahippus leonensis, in the evolution of modern grazing horses of the subfamily Equinae has long been recognized. Several important characteristics suggest an increase in grass consumption in P. leonensis compared to earlier equids, including an increase in molar crown height, presence of cement, increased wear rates, and a dental microwear pattern with an abundance of fine scratches. I used carbon and oxygen stable isotope compositions of a large sample (n=74) of P. leonensis tooth enamel, extracted from along the molar tooth row to control