ABSTRACT Thermoregulation and Dental Isotopes Reveal the Behavior and Environment of Pleistocene Megafauna at Waco Mammoth National Monument Donald A. Esker, Ph.D. Mentor: Steven L. Forman, Ph.D. Waco Mammoth National Monument (WMNM) in central Texas is a significant Pleistocene paleontological site, containing at least 16 Columbian mammoths and specimens of 12 other vertebrate taxa. Interpreting this site, however, is contingent on understanding the environment Pleistocene animals lived in and how they interacted with that environment behaviorally. Actualistic studies of modern analogs can be used to better understand the behavior and geographic range of a Pleistocene animal and thus increase their usefulness as paleoclimate and paleoenvironmental indicators. Mass and thermal modeling studies done on modern tortoises have been used to determine the temperature tolerance of the giant tortoise species of central Texas, constraining the climate present at WMNM during its formation. Understanding the long-term movements of a fossil organism can reflect the environment it lives in. Strontium isotope ratio analysis of megafaunal teeth from WMNM have shown that not all of the mammoths at the site shared a geographic origin. The behavior revealed – mammoths congregated at WMNM from a wide area – necessitated a reconsideration of the long-standing mechanism of death for the megafauna there. Serial analysis of carbon and oxygen isotopes from the same teeth revealed that while the animals at WMNM shared a diet, some may have had distinct sources of drinking water. They also reveal that the WMNM megafauna lived in a drier, more drought-prone world that previously thought. Taking a multi-proxy approach to better understand interactions between Pleistocene megafauna and the environmental changes they experienced should inform our attempts to conserve our remaining megafauna. Thermoregulation and Dental Isotopes Reveal the Behavior and Environment of Pleistocene Megafauna at Waco Mammoth National Monument by Donald A. Esker, B.S., M.S. A Dissertation Approved by the Department of Geosciences ______________________________________ Steven Driese, Ph.D., Chairperson Submitted to the Graduate Faculty of Baylor University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Approved by the Dissertation Committee Steven L. Foreman, Ph.D., Chairperson Rena C. Bonem, Ph.D. Daniel J. Peppe, Ph.D. Steven Dworkin, Ph.D. Ken Wilkins, Ph.D. Elizabeth Petsios, Ph.D. Accepted by the Graduate School December 2019 J. Larry Lyon, Ph.D., Dean Page bearing signatures is kept on file in the Graduate School Copyright © 2019 by Donald A. Esker All rights reserved TABLE OF CONTENTS LIST OF FIGURES .......................................................................................................... vii LIST OF TABLES ........................................................................................................... viii LIST OF EQUATIONS ..................................................................................................... ix ACKNOWLEDGMENTS .................................................................................................. x CHAPTER ONE ................................................................................................................. 1 Introduction ..................................................................................................................... 1 CHAPTER TWO ................................................................................................................ 3 Reconstructing the Mass and Thermal Ecology of North American Pleistocene Tortoises .......................................................................................................................... 3 Abstract ....................................................................................................................... 3 Introduction ................................................................................................................. 4 Methods....................................................................................................................... 8 Results ....................................................................................................................... 14 Conclusions ............................................................................................................... 27 Acknowledgements ................................................................................................... 28 CHAPTER THREE .......................................................................................................... 30 Home Range of the Columbian Mammoths (Mammuthus columbi) and Grazing Herbivores from the Waco Mammoth National Monument, (Texas, USA) Based on Strontium Isotope Ratios from Tooth Enamel Bioapatite ............................................ 30 Abstract ..................................................................................................................... 30 Introduction ............................................................................................................... 31 Geologic Setting........................................................................................................ 33 Methods..................................................................................................................... 37 Results ....................................................................................................................... 46 Discussion ................................................................................................................. 58 Conclusions ............................................................................................................... 60 Acknowledgements ................................................................................................... 61 CHAPTER FOUR ............................................................................................................. 62 Environmental Constraints from Serial δ13C and δ18O Analysis of Teeth from Waco Mammoth National Monument, TX USA .................................................................... 62 Abstract ..................................................................................................................... 62 Introduction ............................................................................................................... 63 Modern Conditions ................................................................................................... 64 Materials & Methods ................................................................................................ 69 v Results ....................................................................................................................... 73 Discussion ................................................................................................................. 82 Synthesis: WMNM ................................................................................................... 89 Acknowledgements ................................................................................................... 92 CHAPTER FIVE .............................................................................................................. 93 Summary and Future Research ..................................................................................... 93 Reconstructing the Mass and Thermal Ecology of North American Pleistocene Tortoises .................................................................................................................... 93 Home Range of the Columbian Mammoths (Mammuthus columbi) and Grazing Herbivores from the Waco Mammoth National Monument, (Texas, USA) Based on Strontium Isotope Ratios from Tooth Enamel Bioapatite .................................... 94 Environmental Constraints from Serial δ13C and δ18O Analysis of Teeth from Waco Mammoth National Monument, TX USA ...................................................... 94 Overall Conclusions .................................................................................................. 95 APPENDIX A ................................................................................................................... 97 Supplementary Data for Chapter Two .......................................................................... 97 APPENDIX B ................................................................................................................... 98 Supplementary Data for Chapter Three ........................................................................ 98 APPENDIX C ................................................................................................................... 99 Supplementary Data for Chapter Four .......................................................................... 99 WORKS CITED ............................................................................................................. 100 vi LIST OF FIGURES Figure 2.1 Selected phylogenies of tortoises .............................................................7 Figure 2.2 3D regression describing cooling .............................................................11 Figure 2.3 Cooling curves for four living tortoises ....................................................14 Figure 2.4 Four linear measurement vs. weight regressions ......................................15 Figure 2.5 Two linear measurement vs. weight regressions