Development, Evolution, and Teeth: How We Came to Explain The Morphological Evolution of the Mammalian Dentition by Katherine MacCord A Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Approved March 2017 by the Graduate Supervisory Committee: Manfred Laubichler, Co-Chair Jane Maienschein, Co-Chair Richard Creath James Hurlbut Lucie Laplane William Kimbel ARIZONA STATE UNIVERSITY May 2017 ABSTRACT This dissertation begins to lay out a small slice of the history of morphological research, and how it has changed, from the late 19th through the close of the 20th century. Investigators using different methods, addressing different questions, holding different assumptions, and coming from different research fields have pursued morphological research programs, i.e. research programs that explore the process of changing form. Subsequently, the way in which investigators have pursued and understood morphology has witnessed significant changes from the 19th century to modern day research. In order to trace this shifting history of morphology, I have selected a particular organ, teeth, and traced a tendril of research on the dentition beginning in the late 19th century and ending at the year 2000. But even focusing on teeth would be impossible; the scope of research on this organ is far too vast. Instead, I narrow this dissertation to investigation of research on a particular problem: explaining mammalian tooth morphology. How researchers have investigated mammalian tooth morphology and what counts as an explanation changed dramatically during this period. i DEDICATION This dissertation is the result of seven years of research. Over seven years, I have received the support of an unbelievable number of people. The degree is for me, but this dedication is for them. With love: My partner in crime. My family. My friends. ii ACKNOWLEDGMENTS I would like to thank Jane Maienschein, Manfred Laubichler, and Lucie Laplane for their intense discussions and feedback on ideas and drafts of this dissertation, as well as the rest of my committee (Rick Creath, Bill Kimbel, and Ben Hurlbut) for their help along the way. I would also like to thank Jukka Jernvall at the University of Helsinki for hosting me in his laboratory during my Fulbright Fellowship and allowing me to become a member of his laboratory, as well as Postdoc, Jacqueline Moustakas-Verho, for her discussions about the history of embryology and turtle biology. Over the years, I have given presentations of different ideas and pieces of chapters at a number of meetings, including, “The Enamel Knot at 100” in Helsinki, Finland, in December, 2013, the Joint Atlantic Seminar for the History of Biology at Johns Hopkins University in April, 2014, the History of Science Society in Chicago, IL, in November, 2014, the PhilBioMed seminar at the Institute for History and Philosophy of Sciences and Technology in Paris, France, in November, 2014, the Pan American Society for Evolutionary Developmental Biology in Berkeley, CA, in August 2015, &HPS6 at the University of Edinburgh in July, 2016, the Marine Biological Laboratory McDonnell Foundation Workshop in November, 2016, and the Mathematical Biosciences Institute Workshop on “The Biological Challenges in Morphogenesis” in February, 2017. This research was completed with funding from the Fulbright Foundation, Finland, the Graduate College at ASU, the Graduate & Professional Student Association at ASU, the School of Life Sciences at ASU, and the Center for Biology and Society at ASU. iii TABLE OF CONTENTS Page LIST OF TABLES ................................................................................................................. vi LIST OF FIGURES ............................................................................................................... vii CHAPTER 1 INTRODUCTION ................. ...................................................................................... .. 1 Morphology Matters ................................................................................. 1 Why Teeth? .............................................................................................. 7 Tooth Development and the Special Characteristics of Teeth ................ 9 Homologies, Types, and the Relationship between Ontogeny and Phylogeny: Morphology in the 19th Century ......................................... 13 Morphology in the 20th Century: From Morphogenesis to a New Intersection of Development and Evolution .......................................... 21 Thesis ...................................................................................................... 24 2 EDWARD DRINKER COPE, HENRY FAIRFIELD OSBORN, AND THE TRITUBERCULAR THEORY ................................................................ 26 Introduction ............................................................................................ 26 Cope, Osborn, and Assumptions ............................................................ 29 Cope’s Understanding of Evolution and Mammalian Molar Complexity ............................................................................................................... .31 Cope’s Tritubercular Theory .................................................................. 37 Cope and the Mechanical Causes of Evolution ..................................... 39 iv CHAPTER Page Recap: Cope, Morphological Complexity, and the Origin of the Tritubercular Theory .............................................................................. 40 Osborn, Mesozoic Mammals, and the Tritubercular Molar .................. 40 Osborn’s Molar Types ............................................................................ 46 Types and Progress ................................................................................. 47 Types and Cusp Homologies ................................................................. 50 Osborn and the Tritubercular Theory ..................................................... 53 The Tritubercular Theory, by the End of the 19th Century .................... 54 Assumptions of the Tritubercular Theory .............................................. 55 3 CARL RÖSE AND THE CONCRESCENCE THEORY ........................................... 57 Introduction ............................................................................................ 57 The Context of Concrescence: Dental Development in the 19th Century ................................................................................................... 59 Röse’s Early Work and the Biogenetic Law .......................................... 63 Röse, Teeth, and the Concrescence Theory ........................................... 66 Reception of Röse’s Work and the Concrescence Theory .................... 76 4 A CONFLICT OF ASSUMPTIONS: TRITUBERCULAR THEORY VERSUS CONCRESCENCE THEORY ................................................................. 79 Introduction ............................................................................................ 79 The Relationship between Assumptions and Theories within the Research of Cope, Osborn, and Röse ..................................................... 80 v CHAPTER Page Statements of the Tritubercular and Concrescence Theories and Assumptions ........................................................................................... 82 The Controversy that Arose Between Assumptions .............................. 83 Challenges to the Tritubercular and Concrescence Theories ................ 86 Theories, Assumptions, and the Fates of the Tritubercular and Concrescence Theories ........................................................................... 91 5 THE ENAMEL KNOT .............. ................................................................................. 94 Introduction ............................................................................................ 94 Discovery of the Enamel Knot: Hans Ahrens, 1913 .............................. 96 Ahrens and the Enamel Knot ............................................................... 100 Summary and Assumptions .................................................................. 104 Erwin Reichenbach, 1926/1928 ........................................................... 105 Reichenbach and the Enamel Knot ...................................................... 109 Summary and Assumptions .................................................................. 112 Nozue and Colleagues, 1971-1973 ...................................................... 113 Summary and Assumptions .................................................................. 120 The Enamel Knot’s Finnish Renaissance: Jukka Jernvall, 1994 ......... 121 Jernvall and the Enamel Knot .............................................................. 123 Summary and Assumptions .................................................................. 127 The Enamel Knot throughout the 20th Century .................................... 129 6 JUKKA JERNVALL, MAMMALIAN MOLAR DIVERSITY, AND BRINGING DEVELOPMENT AND EVOLUTION TOGETHER .......................... 132 vi CHAPTER Page Introduction .......................................................................................... 132 The Structure of this Chapter ............................................................... 134 Morphological Diversity ...................................................................... 139 Evolution of a Cusp: The Hypocone ...................................................