THE BURGESS SHALE: A CAMBRIAN MIRROR FOR MODERN EVOLUTIONARY BIOLOGY by Keynyn Alexandra Ripley Brysse A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Institute for the History and Philosophy of Science and Technology University of Toronto © Copyright by Keynyn Alexandra Ripley Brysse (2008) Library and Bibliotheque et 1*1 Archives Canada Archives Canada Published Heritage Direction du Branch Patrimoine de I'edition 395 Wellington Street 395, rue Wellington Ottawa ON K1A0N4 Ottawa ON K1A0N4 Canada Canada Your file Votre reference ISBN: 978-0-494-44745-1 Our file Notre reference ISBN: 978-0-494-44745-1 NOTICE: AVIS: The author has granted a non­ L'auteur a accorde une licence non exclusive exclusive license allowing Library permettant a la Bibliotheque et Archives and Archives Canada to reproduce, Canada de reproduire, publier, archiver, publish, archive, preserve, conserve, sauvegarder, conserver, transmettre au public communicate to the public by par telecommunication ou par Plntemet, prefer, telecommunication or on the Internet, distribuer et vendre des theses partout dans loan, distribute and sell theses le monde, a des fins commerciales ou autres, worldwide, for commercial or non­ sur support microforme, papier, electronique commercial purposes, in microform, et/ou autres formats. paper, electronic and/or any other formats. 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Canada The Burgess Shale: A Cambrian Mirror for Modern Evolutionary Biology Keynyn Alexandra Ripley Brysse Doctor of Philosophy Institute for the History and Philosophy of Science and Technology University of Toronto 2008 Abstract The Burgess Shale, discovered in 1909, contains the fossilized remains of unusual marine animals from shortly after the Cambrian explosion. This thesis delineates three distinct phases in Burgess Shale research. It examines why the Burgess Shale has inspired such dissimilar interpretations and asks what the consequences of these different views are for our understanding of the tempo and mode of evolution and the place of systematics in evolutionary biology. The Burgess Shale fossils were initially classified by Charles Doolittle Walcott as primitive members of modern groups. Later, in the 1960s, Cambridge (UK) paleontologists, led by Harry Whittington, came to think of the Burgess creatures as unique evolutionary experiments, unrelated to modern animal phyla. This "weird wonders" view was taken to its extreme by Stephen Jay Gould. Gould used the Burgess fossils to advance a highly distinctive theory of the tempo and mode of evolution, and to argue that morphological disparity has decreased over time, not increased as commonly believed. Gould held to this view until his death. The third phase, initiated by Derek Briggs and Simon Conway Morris in the 1980s, gives a very different interpretation to the Burgess Shale. On this new understanding, disparity has not decreased, and the Burgess creatures are no longer weird ii wonders deserving unique phylum status, but are now seen as "stem groups" on the evolutionary paths leading up to the modern phyla. This thesis investigates the motivations of the protagonists in this debate. Briggs and Conway Morris each arrived at their Phase 3 view for different reasons. Briggs credited the adoption of cladistics, a new method of classification. Conway Morris credited the increased information provided by the discovery of new fossils, and the re-interpretation of known fossils. Despite the fact that Gould and Conway Morris both dismissed cladistics as an inadequate tool for the study of biological diversity, they held radically divergent views about the diversity of the Burgess Shale. This dissertation will show that these men had different theories of the tempo and mode of evolution; therefore, each saw the Burgess fossils in the light of his own theories, assumptions, and goals. iii Quotations "Fossils provide just enough data to fuel a debate but not enough to resolve it."1 "It becomes clear that there has been a battle underway to monopolize the Cambrian explosion and impose a story that fits a triumphant set of preconceived notions. So who owns the Burgess Shale now?"2 1 Andrew Berry, "Wonderful crucible," Review of The Crucible of Creation: The Burgess Shale and the Rise of Animals by Simon Conway Morris (Oxford: Oxford University Press, 1998) Evolution vol. 52, no. 5 (October 1998), 1529. 2 Jeffrey Levinton, "Who owns the Cambrian explosion?" Review of The Crucible of Creation: The Burgess Shale and the Rise of Animals by Simon Conway Morris (Oxford: Oxford University Press, 1998) The Quarterly Review of Biology vol. 74, no. 2 (June 1999): 201-204. IV Acknowledgments I would like to thank my supervisor, Denis Walsh, for his excellent advice and tremendous support: intellectual, psychological, and financial. Special thanks are also due to the rest of my dissertation committee, Polly Winsor and Marga Vicedo, and my other final examiners, David Sepkoski and Paul Thompson, who were all kind, supportive, and full of excellent suggestions. Jean-Bernard Caron, Curator of Invertebrate Paleontology at the Royal Ontario Museum, and Allison Daley, a paleontology student currently writing her dissertation on the Burgess Shale, have been frequent and extremely friendly sources of information and encouragement. Athena McKown, who recently received her Ph.D. in botany from the University of Toronto, provided helpful information about the evolution of C4 photosynthesis in plants, and was a valuable source of insight into modern phylogenetic and other scientific practices. She has also been, and continues to be, a huge source of comfort and advice, usually served with tea. I am grateful to John Henry at the University of Edinburgh, who first suggested that the Burgess Shale reclassifications might make a good dissertation topic, and to Christian Baron, a Ph.D. candidate at the University of Copenhagen, who made me aware of Sidnie Manton's connection to the German idealistic morphology tradition. Thanks are also due to Trevor Levere and Isaac Record, Editor-in-Chief and Editorial Assistant ofAnnals of Science, who kindly let me use the Annals scanner to upload images for my thesis. I am also very grateful for the assistance, advice, and support of Denise Horsley and Muna Salloum, who have both reassured and rescued me countless times over the past five years. I would also like to thank the staff of the General and Zoology Library at the British Museum of Natural History, who let me examine and photograph their collection of Sidnie Manton's correspondence. Finally, and most profoundly, I am especially indebted to Derek Briggs, Graham Budd, Simon Conway Morris, Richard Fortey, and Harry Whittington for so kindly and generously taking the time to discuss with me their work on the Burgess Shale. Their ideas, spoken and written, published and unpublished, are the subject of the research described in these pages, and as such my work would not have been possible without their support and very generous assistance. Briggs and Fortey even allowed me to read and photocopy materials of interest from among their unpublished notes and correspondence, which have proven indispensible for my work. v My Ph.D. studies were supported by a Doctoral Fellowship from the Social Sciences and Humanities Research Council of Canada (SSHRC), and also by a Margaret and Nicolas Fodor Fellowship, two travel grants and a bursary from the School of Graduate Studies, and two travel grants from the Institute for History and Philosophy of Science and Technology, all at the University of Toronto. I am very grateful for this financial assistance, as well as the income provided by several teaching and research assistantships and an instructorship, without which I would not have been able to conduct my research. vi Table of Contents Abstract ii Quotations iv Acknowledgments v Table of Contents vii List of Tables , viii List of Figures ix List of Appendices xi Chapter 1 Introduction: "The Single Most Important Fossil Discovery Ever Made" 1 Chapter 2 Cladistics and Stem Groups: "Building a Phylogeny from the Bottom Up" 59 Chapter 3 Conway Morris's Reclassifications: "Fishing in the Cambrian Sea" 120 Chapter 4 The Occupation and Navigation of Morphospace 157 Chapter 5 "The Golden Age of Body Plans:" Phyla in the Burgess Shale 200 Chapter 6 Conclusion: The "Battle" for the Burgess Shale 253 Bibliography 260 Appendix A 289 vii List of Tables Table 1. Appendage Distributions in Modern vs. Burgess Shale Arthropods 22 Table 2. The Three Phases of Burgess Shale Research 52 Table 3. Changing Classifications of Burgess Shale Species 53 viii List of Figures Figure 1. Location of Three Main Burgess Shale Quarries 3 Figure 2. Geological Time Scale ..8 Figure 3. Four Major Arthropod Body Plans 19 Figure 4. Biramous Arthropod Appendage 20 Figure 5. Marretta splendens. 23 Figure 6. Yohoia tenuis 24 Figure 7. Opabinia regalis 26 Figure 8. Nectocaris pteryx... 29 Figure 9. Hallucigenia sparsa (Conway Morris, 1977) 30 Figure 10. Wiwaxia corrugata 31 Figure 11. Anomalocaris canadensis - The Complete Animal 32 Figure 12. Two Models of Morphological Disparity through Time 40 Figure 13. Whittington's Phylogenetic Lawn Diagram 63 Figure 14.