Marshall University Marshall Digital Scholar Theses, Dissertations and Capstones 2014 Shape evolution and sexual dimorphism in the mandible of the dire wolf, Canis Dirus, at Rancho la Brea Alexandria L. Brannick [email protected] Follow this and additional works at: http://mds.marshall.edu/etd Part of the Animal Sciences Commons, and the Paleontology Commons Recommended Citation Brannick, Alexandria L., "Shape evolution and sexual dimorphism in the mandible of the dire wolf, Canis Dirus, at Rancho la Brea" (2014). Theses, Dissertations and Capstones. Paper 804. This Thesis is brought to you for free and open access by Marshall Digital Scholar. It has been accepted for inclusion in Theses, Dissertations and Capstones by an authorized administrator of Marshall Digital Scholar. For more information, please contact [email protected]. SHAPE EVOLUTION AND SEXUAL DIMORPHISM IN THE MANDIBLE OF THE DIRE WOLF, CANIS DIRUS, AT RANCHO LA BREA A thesis submitted to the Graduate College of Marshall University In partial fulfillment of the requirements for the degree of Master of Science in Biological Sciences by Alexandria L. Brannick Approved by Dr. F. Robin O’Keefe, Committee Chairperson Dr. Julie Meachen Dr. Paul Constantino Marshall University May 2014 ©2014 Alexandria L. Brannick ALL RIGHTS RESERVED ii ACKNOWLEDGEMENTS I thank my advisor, Dr. F. Robin O’Keefe, for all of his help with this project, the many scientific opportunities he has given me, and his guidance throughout my graduate education. I thank Dr. Julie Meachen for her help with collecting data from the Page Museum, her insight and advice, as well as her support. I learned so much from Dr. O’Keefe and Dr. Meachen over the past 2 years, and for that I am so grateful. I also thank Dr. Paul Constantino for raising questions that I had not considered, as well as for his suggestions for my thesis. I would also like to thank University of California Museum of Paleontology at Berkeley, specifically Pat Holroyd, and The George C. Page Museum, specifically John Harris, Chris Shaw, Aisling Farrell, and Gary Takeuchi, for allowing Dr. O’Keefe, Dr. Meachen, and I to collect data from the dire wolf specimens used in this project and for their assistance. I also thank Dr. H. David Sheets for his assistance using the IMP programs, including pcagen_7a. I thank the Graduate College for the Marshall University Summer Thesis Award and the Marshall University Drinko Research Fellowship to FRO for funding towards this project. I also thank all of the graduate students of the Biological Sciences, specifically Elise Edwards, Lyndsay Rankin, Mark DeBlois, Derek Breakfield, and Kelli Herrick for their support, encouragement, and their willingness to listen and give feedback on “practice talks” and my work. Finally, I thank my parents, my sisters, and Mike Black for the enormous support system they have provided me, as well as for always encouraging me to follow my dreams. iii ABSTRACT The Rancho La Brea tar pits are a classic fossil lagerstätten, famous for the deposition of episodic accumulations of large numbers of fossils over short intervals in the late Pleistocene. I analyzed 157 Canis dirus (dire wolf) hemi-mandibles from Rancho La Brea through a 2D landmark-based morphometric analysis to test for size and shape changes through time. I scored 16 landmarks on each mandible gathered from four pits of different ages: 61/67 (~13-14 thousand years ago [ka]), 13 (~17-18 ka), 2051 (~26 ka), and 91 (~28 ka). Analyses indicate size does change through time, and shares a broad correlation with climate change. A principal components analysis revealed shape variables also fluctuated from pit to pit. Other environmental effects, such as competition, nutritional stress, and prey-preference, may also vary through time. These effects, along with climate, must be considered in determining the causalities of the size and shape changes we see in the dire wolf jaws. In addition, some sexually dimorphic signals are also distinguishable among the mandibles, and are similar to those seen in the extant gray wolf (Canis lupus). iv CONTENTS Abstract………………………………………………………………………………………….. iv Chapter 1, Introduction……..……………………………………………………………………. 1 Background……………………………………………………………………………. …1 The Origin of Dogs……………………………………………………………………. …2 The Family Canidae………………………………………………………………….... …3 The Dire Wolf………………………………………………………………………..... ..10 Canis dirus and Canis lupus……………………………………………………………..11 Morphological Changes and the Environment………………………………………......12 Study Design…………………………………………………………………………… 14 Chapter 2, Landmark-Based Shape and Size Analyses………………………………………… 18 Materials and Methods…………………………………………………………………. .18 Results………………………………………………………………………………….. .21 Discussion………………………………………………………………………………..26 Chapter 3, Sexual Dimorphism and Allometry…………………………………………………. 33 Introduction………………………………………………………………………………33 Materials and Methods………………………………………………………………….. 36 Results…………………………………………………………………………………....39 Discussion………………………………………………………………………………..46 Literature Cited…………………………………………………………………………………..53 Appendixes………………………………………………………………………………………68 Appendix A: Letter from Institutional Review Board…………………………………...68 Appendix B: List of Specimens, Procrustes Coordinates and Distances………………...69 CHAPTER 1 INTRODUCTION Background The end of the Pleistocene epoch (2.6-0.01 Ma) saw numerous, extreme fluctuations in global climate, as well as the demise of many genera of large mammals (Barnosky et al., 2003; Rahmstorf, 2003; Barnosky et al., 2004; Koch and Barnosky, 2006). The causality of these global extinctions are contentious, but some combination of climate change and overkill by humans is the current consensus (Koch and Barnosky, 2006; Gill et al., 2009; MacDonald et al., 2012; Guthrie, 2006; Nogues-Bravo et al., 2008). Analyzing the structure of the fossil communities leading up to the end Pleistocene megafaunal extinctions may allow for clearer interpretations of the causalities of these extinctions. The Rancho La Brea tar pits are located in Los Angeles, California. They are famous for the deposition of episodic accumulations of large numbers of fossils during the terminal Pleistocene (Stock and Harris, 1992). These asphaltic seeps range in age from ~50,000-10,000 years ago (O’Keefe et al., 2009). The pits formed when Paleogene oil deposits migrated to the surface and formed open pools where plants and animals became entrapped. The open seeps were then covered by alluvial sediments (Quinn, 1992; Frisca et al., 2008; O’Keefe et al., 2009). Radiocarbon dating has provided depositional time frames for each pit, and the foundation of a climate correlation to these times of deposition. The La Brea tar pits are exceptional and offer an important opportunity to study fossil communities through dramatically varying Pleistocene climates (Stock and Harris, 1992; Meachen et al., 2014; O’Keefe et al., 2014). Carnivores are found in high proportions in the pits at Rancho La Brea; a ratio of 10 carnivores for every 1 herbivore, the opposite of what is seen in nature and at most fossil sites 1 (Stock and Harris, 1992; Binder and Van Valkenburgh, 2010). This disparity is due to the method of entrapment at the tar pits, where one herbivore became mired in the tar and attracted a large number of carnivores, which then became mired themselves. Carbone et al. (2009) suggested a carcass domination scenario, where large, social carnivores were more likely to become entrapped due to greater attraction to the sights and sounds of easy prey and the willingness to challenge other predators for this opportunity. A recent study supported this hypothesis by reporting significantly higher social carnivoran abundance at Rancho La Brea in comparison to the fauna of Southern California and North America as a whole (McHorse et al, 2012). The most common species at Rancho La Brea is the dire wolf, Canis dirus (Leidy, 1854), an extinct wolf species endemic to North and South America (Dundas, 1999). The dire wolf comprises over 50 % of the relative abundance of carnivorans at Rancho La Brea (McHorse et al., 2012). Because of the large numbers of dire wolf fossils, and the radiocarbon dating of each pit, C. dirus is an excellent species for the examination of shape over time at Rancho La Brea. The dire wolf is classified as a carnivoran within the family Canidae (Tedford et al., 2009), and it will be the focus species of this project. The Origin of Dogs. The order Carnivora appeared in the early Paleocene (65-60 Ma) and encompasses a great diversity of mammalian lineages, including 11 extant families (Van Valkenburgh, 2007). The first true carnivorans, diagnosed by the presence of derived teeth called carnassials, reside in the extinct family Viverravidae, and spread throughout most of the world during the early Tertiary. Determining this lineage as a progenitor for later carnivorans, including the families Felidae and Hyaenidae, has remained controversial (Polly et al., 2006; Wang and Tedford, 2008). Fossil remains of viverravids are rare, and gaps in the fossil record complicate reconstructions of phylogenetic relationships. Evidence of plesiomorphic 2 characteristics within the auditory bulla of Viverravus acutus place viverravids outside of crown- group Carnivora, indicating this family probably did not give rise to the extant members of this order. The family Miacidae, another ancient lineage of early carnivorans, is thought to be the ancestor of many, if not all, modern families within Carnivora (Polly et al., 2006; Heinrich et al.,