Patterns of Variance and Covariance in Anthropoid Limb Proportions: Implications for Interpreting the Hominin Fossil Record
Total Page：16
File Type：pdf, Size：1020Kb
Patterns of Variance and Covariance in Anthropoid Limb Proportions: Implications for Interpreting the Hominin Fossil Record by Vance C. R. Powell B.A. in Anthropology, December 2011, University of South Florida M.Phil. in Hominid Paleobiology, June 2016, The George Washington University A Dissertation submitted to The Faculty of The Columbian College of Arts and Sciences of the George Washington University in partial fulfillment of the requirements for the degree of Doctor of Philosophy August 31, 2018 Dissertation directed by Bernard A. Wood University Professor of Human Origins The Columbian College of Arts and Sciences of The George Washington University certifies that Vance C. R. Powell has passed the Final Examination for the degree of Doctor of Philosophy as of May 11, 2018. This is the final and approved form of the dissertation. Patterns of Variance and Covariance in Anthropoid Limb Proportions: Implications for Interpreting the Hominin Fossil Record Vance C. R. Powell Dissertation Research Committee: Bernard A. Wood, University Professor of Human Origins, Dissertation Director Sergio Almécija, Assistant Research Professor of Anthropology, Committee Member W. Andrew Barr, Visiting Assistant Professor of Anthropology, Committee Member ii Dedication This dissertation is dedicated to all those instructors who are responsible for instilling in me a love of science and the motivation to pursue an advanced degree in a STEM field. To my high school science instructor, Robert Geach, who encouraged the friendly rivalry for best grades between myself and classmate Nia Mapp. Despite being a Christian private school instructor, Mr. Geach always answered questions about evolution directly and honestly. To my instructors from the University of South Florida, Melissa Pope, Edgar Amador, Michelle Raxter, and Thomas Pluckhahn. For me, these individuals laid the founding knowledge about the four fields of anthropology, and I thank them for dealing with my endless questions. To my family, my mother, my sister Nikki (aka, Peyton), my brothers Khnum (aka, Mark) and Terry, and my partner Desiree. Without your influences early in my life, and your encouragement and support throughout my academic career, I would not have made it this far. iii Acknowledgements I would like to begin by thanking my graduate school advisor, Dr. Bernard A. Wood. Bernard’s is among the first paleoanthropological research with which I became familiar during undergraduate studies. I will never underestimate how fortunate I am to have worked under his guidance, and to have had his support during the emotionally, intellectually, and financially trying graduate school experience. I have not been an easy student to work with, but I am immensely grateful. I would also like to thank my other committee members and examiners, Drs. Sergio Almécija, W. Andrew Barr, Ashley Hammond, and Adam Gordon, who, despite having no obligation to me as an individual or student, dedicated countless hours to reviewing, editing, and offering comments on my thesis. In the time we worked together I have learned more about producing good research than I can account for here. I also acknowledge the students and other faculty at the George Washington University (GWU), and especially in the Center for the Advanced Study of Human Paleobiology (CASHP). Like my committee members, many offered ideas to help me form my thesis topic, reviewed drafts of other projects, and others offered their companionship. I am particularly thankful for the latter, as the last 5 and a half years, during which I’ve seen my family only very rarely, have proven to be particularly lonely, especially considering the “social butterfly” I had frequently been described as during my undergraduate. Finally, I would like to thank the George Washington University and the National Science Foundation, which funded my research and studies. iv Abstract of Dissertation Patterns of Variance and Covariance in Anthropoid Limb Proportions: Implications for Interpreting the Hominin Fossil Record Interpreting the taxonomic and behavioral implications of variation in the inferred limb proportions of fossil hominin taxa is contingent upon assessing how much variation exists in extant primate taxa and, by extension, how much of that variation is associated differences in their locomotor behaviors. However, the majority of evidence linking limb proportions to behavior in extant primates is based on taxonomically-restricted samples, or on species means as opposed to individual values, or does not account for field observations that capture the complexity of locomotor behavior in a primate taxon (see Napier & Napier, 1967; Fleagle, 1988; see also Preuschoft, 2002). With regards to extinct taxa, the problem is compounded by a necessary reliance on relatively few associated skeletons, most of which are incomplete, or fragmented or both. This thesis addresses the aforementioned issues using a) multivariate methods to quantify the relationships between limb proportions and behavioral repertoires in extant anthropoids; b) machine-learning methods to select relevant extant models with which to interpret the limb proportions of extinct taxa; and c) resampling methods to evaluate hypotheses regarding major adaptive shifts in inferred locomotor behavior. v Table of Contents Dedication iii Acknowledgements iv Abstract of Dissertation v List of Figures viii List of Tables ix Chapter 1: Introduction 1 Extant primate locomotion 3 Primate limb proportions 4 Inferring behavior from fossil hominin 5 skeletons Thesis outline and goals 18 Chapter 2: Phylogenetic and functional signals of anthropoid limb 21 proportions Abstract 21 Introduction 22 Materials and Methods 27 Sample 27 Analytical methods 29 Results 38 Discussion 46 Chapter 3: Are extant apes appropriate models for hominin limb proportions? 75 Insights from machine learning analyses Abstract 75 Introduction 77 Materials and Methods 80 Extant training sample 80 Fossil sample 80 Analytical methods 84 Results 89 Discussion 91 Chapter 4: Evaluating hominin locomotor grades 113 Abstract 113 vi Introduction 114 Materials and Methods 117 Fossil specimens 117 Comparative sample 118 Analytical methods 118 Results 121 Discussion 125 Chapter 5: Conclusion 135 Bibliography of References 141 Appendix 181 vii List of Figures Chapter 2 figures 54 Figure 2.1. Measurements 54 Figure 2.2. Phylogenetic tree 55 Figure 2.3 a&b. Box plots 56 Figure 2.4 a&b. PCA 58 Figure 2.5 a-c. 2-BPLS 60 Figure 2.6. Phylomorphospace 63 Chapter 3 figures 98 Figure 3.1 a-d. CART decision trees 98 Figure 3.2. Comparative PCA 102 Figure 3.3 a&b. Comparative box plots 104 Chapter 4 figures 129 Figure 4.1 a&b. Genus distributions 129 Figure 4.2. Putative “grade” distributions 131 viii List of Tables Chapter 2 tables 64 Table 2.1. Anthropoid sample 64 Table 2.2. Average percent inter-observer error per taxon 65 Table, 2.3. Tukey’s HSD results 66 Table 2.4. PCA loadings 67 Table 2.5. Percent locomotor behavior 68 Table 2.6. Percent positional behavior 70 Table 2.7 a-c. 2-BPLS scores 71 Table 2.8. Phylogenetic signal 74 Chapter 3 tables 106 Table 3.1. CART validation results 106 Table 3.2. Published fossil sample 107 Table 3.3. Fossil regression estimates 108 Table 3.4 a-d. Regression formulae 109 Chapter 4 tables 132 Table 4.1. Extant sample 132 Table 4.2. Fossil specimens 133 Table 4.3. Arithmetic index differences and percentile values 134 ix Chapter 1: Introduction Two of the major competing hypotheses about variation in the inferred limb length proportions of hominins have posited either taxic diversity, or major adaptive shifts from more ape-like to more modern human-like ancestors with occasional “reversals” to more ancestral phenotypes (Hartwig-Scherer and Martin, 1991; Wood and Richmond, 2000; Richmond et al., 2002; Harcourt-Smith and Aiello, 2004; Berger, 2010; Harcourt-Smith, 2015). However, testing hypotheses about the significance of variation for interpreting fossil behavioral differences is hampered by uncertainty about hominin alpha taxonomy (i.e., the number of taxa represented in the hominin fossil record) and how morphology (e.g., limb proportions) is related to locomotor behavior in extant taxa (see Wood & Boyle, 2016; Villmoare, 2018; Hunt et al., 2016). To address these points, comparative approaches are used to investigate the relationship between variation in limb proportions and behavior in extant primate taxa, and then these relationships are used as reference points against which to interpret the variation among fossil hominins (see Ackermann & Smith 2007). Research addressing these points must contend with the fact that most of the critical fossil evidence about the limb proportions of early hominins comes from incomplete and fragmentary skeletons (e.g., OH 62, BOU-VP 12/1) (Johanson et al., 1987; Asfaw et al., 1999; see also Harcourt-Smith, 2007). Moreover, some of these skeletons, such as those assigned to Homo habilis (OH 62) and Australopithecus garhi (BOU-VP-12/1), suggest reversions to more primitive or ‘ape-like’ body proportions (e.g., relatively longer forelimbs and radii) when compared to Australopithecus afarensis (Johanson et al., 1987; White, 1980; White et al., 1981; White & Suwa, 1987; Asfaw et 1 al., 1999; but see Stern & Susman, 1983; Tuttle, 1984, 1990, 1991; and Harcourt-Smith & Hilton, 2005 for alternative interpretations). However, those claims have not been carefully evaluated against appropriate comparative samples to determine if the fossil variation actually exceeds extant variation (White,