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Phylogenetic Character Analysis of Crocodylian Enamel Microstructure and Its Relevance to Biomechanical Performance Jennifer Erin Creech

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Phylogenetic Character Analysis of Crocodylian Enamel Microstructure and Its Relevance to Biomechanical Performance Jennifer Erin Creech Florida State University Libraries Electronic Theses, Treatises and Dissertations The Graduate School 2004 Phylogenetic Character Analysis of Crocodylian Enamel Microstructure and Its Relevance to Biomechanical Performance Jennifer Erin Creech Follow this and additional works at the FSU Digital Library. For more information, please contact [email protected] THE FLORIDA STATE UNIVERSITY COLLEGE OF ARTS AND SCIENCES PHYLOGENETIC CHARACTER ANALYSIS OF CROCODYLIAN ENAMEL MICROSTRUCTURE AND ITS RELEVANCE TO BIOMECHANICAL PERFORMANCE By JENNIFER ERIN CREECH A Thesis submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of Master of Science Degree Awarded: Spring Semester, 2004 The members of the Committee approve the thesis of Jennifer Erin Creech defended on March 29th, 2004. _____________________ Gregory M. Erickson Professor Directing Thesis _____________________ Scott J. Steppan Committee Member _____________________ Joseph Travis Committee Member Approved: _______________________________________________________ Timothy S. Moerland, Chairman, Department of Biological Science _______________________________________________________ Donald Foss, Dean, College of Arts and Sciences The Office of Graduate Studies has verified and approved the above named committee members. ii This research is dedicated to the memory of my mother Jessica Irene Buchanan Creech who passed away during my first year of graduate work. She taught me to see the world through open eyes; her dedication to her work taught me to appreciate science, her dedication to her family always made me feel loved. I wish she could be here to see what I have accomplished by following in her footsteps. iii ACKNOWLEDGEMENTS I want to thank my family for believing in me. Whenever I was in doubt they were sure to know just what to say to get me back on track. Throughout my time at Florida State University there were people who were vital in helping me complete my research. I would like to thank Greg Erickson for always involving me in his research and his input and help with my own research as well as his support during my mother's death. I also would like to thank the rest of my committee; Scott Steppan and Joe Travis for their help and input throughout my research. Jill Holliday's constant support, advice, and encouragement throughout my undergraduate and graduate education were always appreciated. Thank you Jill for getting me interested in research. All of my specimens were the result of the help of Tony Hunter, the St. Augustine Alligator Farm and Zoological Park in St. Augustine, Florida, and the Gladys Porter Zoo in Brownsville, Texas. Many thanks to Kim Riddle and John Ekman from the Florida State University Biological Science Imaging Resource for all of their assistance with my samples and scanning electron microscopy. I am grateful to Sunny Hwang for an endless supply of enthusiasm and an open mind. Michelle Stuckey and the members of EERDG contributed helpful input on my Natural history presentation. And many thanks to James Albright, Sara Tso, and Stacey Halpern for reading so many drafts of my manuscript and making many valuable comments that have improved the final product immeasurably. iv TABLE OF CONTENTS List of Tables ............................................................................................................................... vii List of Figures.............................................................................................................................. viii Abstract ...................................................................................................................................... ix INTRODUCTION ...........................................................................................................................1 1. THE EVOLUTION OF PRISMLESS ENAMEL MICROSTRUCTURE WITHIN THE CROCODYLIA.................................................................................................................9 Introduction..........................................................................................................................9 Materials and Methods.......................................................................................................12 Specimen selection Element selection Specimen preparation Scanning electron microscope examination Character assignments Statistical analyses Results................................................................................................................................15 Discussion..........................................................................................................................17 Conclusions........................................................................................................................19 2. MICRO-SCALE EFFECTS ON THE MECHANICAL PROPERTIES OF PRISMLESS TOOTH ENAMEL AS A RESULT OF MUSEUM PREPARATION TECHNIQUES.........27 Introduction........................................................................................................................27 Materials and Methods.......................................................................................................29 Specimen selection Element selection Specimen preservation methods Specimen preparation for nanoindentation testing Specimen preparation for scratch testing Material testing Statistical analyses Results................................................................................................................................34 Discussion..........................................................................................................................34 v Conclusions .......................................................................................................................36 3. ENAMEL MICROSTRUCTURAL VARIATION AND BIOMECHANICAL PROPERTIES TESTING: AN INTEGRATIVE APPROACH ..............................................45 Prismless enamel microstructure evolution within the Crocodylia ...................................45 Micro-scale effects on the mechanical properties of prismless tooth enamel ...................46 APPENDIX A................................................................................................................................47 APPENDIX B ................................................................................................................................49 REFERENCES ..............................................................................................................................50 BIOGRAPHICAL SKETCH .........................................................................................................59 vi LIST OF TABLES 1. Species examined within the Crocodylia listed in alphabetical order. ...................................20 2. Summary of grinding and polishing steps ................................................................................21 3. Consistency indices (CI) and rescaled consistency indices (RC) for all microstructural characters described in Appendix A. ......................................................................................22 4. Test parameters assigned to the nanoindentation test procedure. ..........................................37 5. The mean values ± SD of the Vicker's hardness (Hv) and Young's modulus (E) of the enamel 40µm from the enamel edge for the three treatments. .........................................38 6. Two-level nested ANOVA on Vicker's hardness (Hv). ..........................................................39 7. Two-level nested ANOVA on Young's modulus (E). ..........................................................40 vii LIST OF FIGURES 1. Cross-section through the tooth crown (A) and longitudinal section through the jaw and tooth (B) of a crocodylian showing the major components of the tooth. ...........................8 2. Diagram of a caniniform tooth. ..............................................................................................23 3. Three separate preparations from different orientations are necessary to characterize the 3-dimensional structure of crocodylian tooth enamel: longitudinal (A), cross- sectional (B), and tangential (C). ...........................................................................................24 4. Cutting diagram of caniniform tooth for microstructural examination using SEM (A). .......25 5. Microstructural character variation mapped onto the robust crocodylian phylogeny (Gatsey et al. 2004). ...............................................................................................................26 6. Cutting diagram of teeth used in biomechanical properties study. ........................................41 7. Cross-section of a crocodylian tooth. .....................................................................................42 8. Mean hardness (Vickers) values by treatment technique. ......................................................43 9. Mean Young's modulus (GPa) by treatment technique. .........................................................44 viii ABSTRACT Tooth enamel microstructure has been shown to vary among mammals. Such variation has a major bearing upon whole-tooth biomechanical function and may reflect gross-level phylogenetic signal. Although variation is substantial within reptilian lineages, comprehensive standardized sampling has not been done from which a similar understanding can be garnered. In the present study I sampled caniniform teeth from the
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