UNIVERSITY OF CINCINNATI Date:___________________ I, _________________________________________________________, hereby submit this work as part of the requirements for the degree of: in: It is entitled: This work and its defense approved by: Chair: _______________________________ _______________________________ _______________________________ _______________________________ _______________________________ TAPHONOMY OF THE MOTHER’S DAY QUARRY: IMPLICATIONS FOR GREGARIOUS BEHAVIOR IN SAUROPOD DINOSAURS A thesis submitted to the Division of Research and Advanced Studies Of the University of Cincinnati in partial fulfillment of the requirements of the degree of MASTER OF SCIENCE In the Department of Geology of the College of Arts and Sciences 2004 by Timothy S. Myers B.A. & B.S., Rice University, 2002 Committee Chair: Dr. Glenn W. Storrs ABSTRACT The Mother’s Day Quarry, located in the Upper Jurassic Morrison Formation of south-central Montana, contains the remains of a number of immature diplodocid sauropod dinosaurs. If the sauropod individuals were initially part of a herd group, the site would be one of only a few thought to provide skeletal evidence of gregarious behavior in sauropods. To date, none of these sites has been taphonomically constrained in order to determine if they do, in fact, contain the remains of a herd; our only reliable data on sauropod herds currently comes from the ichnological record, which often provides conflicting information. Therefore, the Mother’s Day site has the potential to reveal interesting details of sauropod behavior and clarify ambiguities in the trackway data. This study determines the suitability of the Mother’s Day Quarry as a basis for behavioral interpretations. By reconstructing the taphonomic history of the assemblage, potential biases may be identified, and their implications explored. Analysis of the site reveals that post-mortem biases are minimal, and the sauropods in the quarry likely represent the remnants of a mobile social group. The absence of mature adult individuals in the assemblage appears to be real, and is probably the result of age segregation of some sauropod herd groups. ii iii ACKNOWLEDGEMENTS I would like to start by thanking my committee chair, Dr. Glenn Storrs, for his valuable guidance and support throughout the course of this research. His careful editing and insightful comments have made this a much better document than it would otherwise be. I would also like to thank my other committee members, Dr. Carlton Brett and Dr. David Meyer, for the helpful suggestions and candid assessments that they provided in committee meetings and on the initial draft of this work. Dr. Warren Huff patiently provided much needed assistance with the XRD portion of this study, for which I am most grateful. I am also grateful for the dedication and stoicism of my field crews in Montana. Dr. Jim Clark, Peter Falkingham, Dale Gnidovec, Angela Horner, Ben Otto, Sam Perry, Ji-Yeon Shin, and Shizuko Watanabe all have my gratitude for working tirelessly in the hot sun to help collect data and fossils. I owe an equal debt to all the volunteers in the Museum Center Paleo Lab, who spent so many hours preparing Mother’s Day material, especially Charlotte Cox. Their help was indispensable. I would like to thank Dr. Kristi Curry-Rogers for the use of her field notes from the 1995 and 1996 seasons, which proved invaluable for improving the MNI estimate for the assemblage. She and Dr. Ray Rogers have been a source of continual support and encouragement from the first summer I spent at the site. I am especially grateful to Mike Papp, who often spent his entire weekends in the lab preparing Mother’s Day specimens. He was also a pleasure iv to work with in the field, both for his skill at excavation and his delightful company. Finally, I must thank Bill Garcia for his constant support in the field and in the office. He has lent his valuable proofreading skills on more than one occasion and has been a source of knowledge, advice, and constant friendship throughout this project. Financial support for this research was provided by the Cincinnati Museum Center, a summer research stipend from the University of Cincinnati Department of Geology, and grants from Sigma Xi, the Jurassic Foundation, and the Theodore Roosevelt Memorial Fund of the American Museum of Natural History. v TABLE OF CONTENTS ABSTRACT ......................................................................................................................ii ACKNOWLEDGEMENTS ...............................................................................................iv LIST OF FIGURES .......................................................................................................... 3 LIST OF TABLES............................................................................................................ 5 LIST OF EQUATIONS ..................................................................................................... 6 CHAPTER 1. Taphonomy of the Mother’s Day Quarry INTRODUCTION............................................................................................................. 7 PREVIOUS WORK.......................................................................................................... 9 REGIONAL GEOLOGY ................................................................................................. 10 STRATIGRAPHY .......................................................................................................... 11 REGIONAL PALEOCLIMATIC SETTING...................................................................... 17 METHODOLOGY.......................................................................................................... 19 Field Methods..................................................................................................... 19 Lab Methods....................................................................................................... 24 TAPHONOMY ............................................................................................................... 27 GEOLOGICAL EVIDENCE.............................................................................................. 27 Sedimentology.................................................................................................... 27 BIOLOGICAL EVIDENCE ............................................................................................... 45 Element Location................................................................................................ 45 Element Orientation............................................................................................ 48 Voorhies Groups................................................................................................. 54 Bone Modification ............................................................................................... 56 Preservation Pattern........................................................................................... 61 Taxonomic Diversity ........................................................................................... 68 Number of Individuals......................................................................................... 71 Age Profile.......................................................................................................... 72 DISCUSSION................................................................................................................ 76 CONCLUSIONS............................................................................................................ 82 1 CHAPTER 2. Implications for Gregarious Behavior in Sauropod Dinosaurs INTRODUCTION........................................................................................................... 85 DEFINITION OF A HERD ............................................................................................. 86 ICHNOLOGICAL EVIDENCE........................................................................................ 87 LIMITS OF THE ICHNOLOGICAL RECORD ................................................................ 89 TAPHONOMIC CONSTRAINTS FOR SKELETAL EVIDENCE .................................... 92 MOTHER’S DAY QUARRY........................................................................................... 93 OTHER POSSIBLE HERD ASSEMBLAGES ................................................................ 98 BEHAVIORAL INFERENCES ....................................................................................... 99 CONCLUSIONS.......................................................................................................... 102 REFERENCES............................................................................................................ 103 APPENDIX .................................................................................................................. 114 2 LIST OF FIGURES Figure 1. Map of Montana .............................................................................................. 8 Figure 2. Map of the Bighorn Basin............................................................................... 12 Figure 3. Extent of the Morrison Formation. .................................................................. 13 Figure 4. Percent smectite in the Morrison section on the Colorado Plateau. ............... 16 Figure 5. Percent smectite in the Morrison section at the Mother’s Day site ................. 16 Figure 6. Lithologic logs for the Morrison section at