Mandibular Growth in Australopithecus robustus by Zachary Daniel Cofran A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Anthropology) in the University of Michigan 2012 Doctoral Committee Professor, Milford H. Wolpoff, Chair Professor, Laura M. MacLatchy Assistant Professor, Eric A. Hetland Assistant Professor, Adam P. Van Arsdale, Wellesley College © Zachary Cofran All rights reserved 2012 Acknowledgements There is absolutely no way I could have done any of this work, or survived any of the last five years, on my own. There are a number of people I wish to thank for their help and support along the way. I have learned a tremendous amount about my field, the world, and the secrets of comedy from my advisor Milford Wolpoff, and I am very fortunate to’ve stood on his anthropological shoulders. I have also benefited tremendously from the sagacity and advice of Adam Van Arsdale, regarding this dissertation and especially fieldwork. These two and the rest of my committee, Laura MacLatchy and Eric Hetland, have been extremely patient and helpful in making this dissertation possible. And the past five years could not have gone as smoothly without the UM biological anthropology faculty, who have been exquisite mentors and friends. I would not have survived a day of fossil research without the assistance of Stephany Potze, Laz Kgasi, and Tersia Perregil at the Ditsong National Museum. Not only did they help me in my time crunch, but they also helped me navigate the left-sided streets of Gauteng on my own. Good company and good advice from my cottage roommates Justin Adams and Anthony Kegley made a good research trip great. I am very grateful to the Anthropology department and graduate students of Kent State University. Richard Meindl provided very generous access to the Libben collection, and I could not have navigated it without his and Mary Ann Raghanti’s help. I am ever indebted to Caroline Tannert and Aidan Ruth who really made me feel at home in Kent. ii My friends at the University of Michigan, especially anthropologists, but especially my bioanthrobuddies, made this journey unforgettable. They were always there to help me get into, or out of, trouble – whichever was appropriate at the time. Dana Begun deserves special mention for helping me stay sane all the while. Last and most certainly not least, I owe all I am and all I have to the love and support of my family, the Cofrans and Stuckeys. iii Table of Contents Acknowledgements ...............................................................................................ii List of Figures ....................................................................................................... v List of Tables ........................................................................................................vi List of Appendices ............................................................................................... vii Abstract .............................................................................................................. viii Chapter 1 Introduction .......................................................................................... 1 Chapter 2 Background and Theoretical Contexts ................................................. 8 Chapter 3 Materials and Methods ....................................................................... 40 Chapter 4 Results of the Test .......................................................................... 65 Chapter 5 Implications of A. robustus mandibular growth ................................ 116 Chapter 6 A Look Back and Ahead .................................................................. 158 Bibliography ...................................................................................................... 193 iv List of Figures Figure 1 The Australopithecus robustus ontogenetic series from Swartkrans ....... 3 Figure 2.1. Schematic of how species’ morphology might arise in ontogeny ......10 Figure 2.2. Schematic of facial rotation in A. robustus. ....................................... 14 Figure 2.3. Sampling possibilities created by cross-sectional data. .................... 35 Figure 3.1. The randomization strategy employed in the test. ......................... 61 Figure 4.1. Comparison of A. robustus and human pairwise size metrics (geometric mean of measurements shared in pairwise comparisons) ......... 68 Figure 4.2. A. robustus (blue) and human (green) pairwise sizes across ontogeny ................................................................................................................................... 69 Figure 4.3. statistics for the overall size metric for all pairwise combinations of differently-aged humans ........................................................................................ 72 Figure 4.4 statistic for the overall size metric comparing successive dental eruption stages. ...................................................................................................... 73 Figure 4.5. The number of traits shared between individuals in the test validation ..................................................................................................... 75 Figure 4. the test validation ........................................................................................ 76 Figure 4.7. The number of traits (k) shared between specimens spanning different eruption stages .............................................................................. 78 Figure 4.8. statistics for species difference in overall size change between all eruption stages ............................................................................................ 82 Figure 4.9.ζstatistics for interspecific difference in relative size change between successive eruption stages ......................................................................... 85 Figure 4.10: The effects of preservation on the value of ...................................... 87 Figure 4.11. Distribution of for each difference between eruption stages ........ 90 Figure 4.12. The distributions of all possible interspecificζstatistics for each individual trait .............................................................................................. 92 Figure 4.13. Comparison of the statistic for individual traits and for the pairwise size metric across ontogeny ...................................................................... 110 Figure 5.1. Distribution of statistics measuring difference in overall size change, from the validation and interspecific tests .................................................. 121 Figure 5. 2. The relationship between the value of and the number of traits used to calculate ..................................................................................... 122 Figure 5.3. All statistics for height at the mandibular symphysis and at the ramus ........................................................................................................ 139 v List of Tables Table 3.1. Provenience and catalog numbers of Australopithecus robustus specimens in this analysis. .......................................................................... 42 Table 3.2. Sample sizes for each eruption stage ................................................ 48 Table 3.3. List and description of measurements. .............................................. 56 Table 3.4. Sample metadata (aside from the statistic) stored for each resampled comparison ................................................................................ 62 Table 4.1. Species’ average pairwise size in each eruption stage ...................... 69 Table 4.2. statistics for the overall size metric comparing the human sample with itself. ..................................................................................................... 71 Table 4.3. Relationship between resampled and metadata ............................. 74 Table 4.4. Species difference in relative change for the pairwise size metric (geometric mean). ....................................................................................... 81 Table 4.5. Relationship between resampled and metadata. ............................ 86 Table 4.6. Summary of statistics comparing humans and A. robustus for each trait, across all age comparisons. ................................................................ 96 Table 4.7. statistics comparing humans and A. robustus for each trait between successive eruption stages ......................................................................... 99 Table 4.8. Position of the ramus root across eruption stages in each species.. 100 vi List of Appendices Appendix I: Raw measurements plotted against eruption stage………………..171 Appendix II: “Robusticity index” plotted against eruption stage…………………186 Appendix III: R codes for analyses…………………………………………………190 vii Abstract Mandibular growth in Australopithecus robustus by Zachary Daniel Cofran Chair: Milford H. Wolpoff This dissertation tests the hypothesis that humans’ unique pattern of growth was present in our fossil relative, Australopithecus robustus. Growth and development encompass the mechanisms and processes that bring about morphological variation and adaptation. Growth is also an important life history variable influencing both an animal’s energy requirements and how it is treated by predators and conspecifics. Humans’ unique pattern of growth, featuring long juvenile and childhood phases of slow