University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1989 Taphonomy of three monospecific dinosaur bone beds in the Late Cretaceous Two Medicine Formation northwestern Montana: Evidence for dinosaur mass mortality related to episodic drought Raymond R. Rogers The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Rogers, Raymond R., "Taphonomy of three monospecific dinosaur bone beds in the Late Cretaceous Two Medicine Formation northwestern Montana: Evidence for dinosaur mass mortality related to episodic drought" (1989). Graduate Student Theses, Dissertations, & Professional Papers. 5871. https://scholarworks.umt.edu/etd/5871 This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. COPYRIGHT ACT OF 1975 Th is is an unpublished m anuscript in which copyright SUBSISTS. A ny further r e p r in t in g of it s contents must be APPROVED BY THE AUTHOR. Mansfield Library University of Montana Date ; 1 9 B3 TAPHONOMY OF THREE MONOSPECIFIC DINOSAUR BONE BEDS IN THE LATE CRETACEOUS TWO MEDICINE FORMATION, NORTHWESTERN MONTANA; EVIDENCE FOR DINOSAUR MASS MORTALITY RELATED TO EPISODIC DROUGHT by Raymond R. Rogers B.S. Northern Arizona University, 1985 Presented in partial fulfillment of the requirements for the degree Master of Science University of Montana 1989 Approved by: Ccy^j^airman, Board of Examiners ----------------- Co-Chairman, Board of Examiners Derfh, Graduate School ^ i kL '/ Date UMI Number: EP36672 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMT DituMTtaéon RjMuUiiing UMI EP36672 Published by ProQuest LLC (2013). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProOuesf ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 Rogers, Raymond R., M.S., June 1989 Geology Taphonomy of Three Monospecific Dinosaur Bone Beds in the Late Cretaceous Two Medicine Formation, Northwestern Montana: Evidence for Dinosaur Mass M ortality Related to Episodic Drought (102 pp.) D irectors: John R. Horner Donald Winston ^ Monospecific and "single-species dominated" dinosaur bone beds are relatively common within the alluvial sedi­ ments of the Late Cretaceous (Campanian) Two Medicine Formation of northwestern Montana. Taphonomic analysis of three monospecific dinosaur bone beds in the upper litho- facies of the formation suggests dinosaur mass mortality related to episodic drought. Two of the bone beds. Canyon Bone Bed and Dino Ridge Quarry, preserve the remains of an as yet undescribed species of S tyrac osaurus. The third bone bed, Westside Quarry, preserves skeletal remains of undescribed prosauralophan hadrosaurs. Taphonomic and geo­ logic data indicate that all three dinosaur quarries are autochthonous, non-catastrophic mass mortality fossil assemblages. The styracosaurs in Canyon Bone Bed and Dino Ridge Quarry are buried in shallow, vegetated oxbow lake paleoenvironments. The prosauralophan hadrosaurs of West- side Quarry are interred within and around what may have been an ephemeral floodplain water hole. Pa le oc11 matic data suggest that the Two Medicine coastal plain was affected by a seasonal, semiarid, and warm climate during the la te s t Campanian. Each of the three bone beds is S t ratigraphically associated with sediments reflecting ab­ normally dry conditions, and I propose that episodic regional drought, and resultant malnutrition and disease, lead to the mass mortality events responsible for all three bone beds. Assuming a genetic re latio n sh ip between drought and the three bone beds, certain autécologie inferences can be drawn. The styracosaurs preserved within Canyon Bone Bed and Dino Ridge Quarry and the prosauralophan hadrosaurs of Westside Quarry may have been water-dependent species. During periods of drought, these particular dinosaurs may have had to remain close to perennial water sources. The monospecific nature of the quarries suggests that the dino­ saur species under investigation were probably social, herding animals during periods of water-stress, possibly year-round. Partitioning of dry season resources by dino­ saurs on the Two Medicine coastal plain, trophic dynamics, and interspecific aggression and territorial behavior are all possible motives behind the monospecific character of the three bone beds. 11 ACKNOWLEDGMENTS I would like to express my sincere gratitude to the mem­ bers of my thesis committee: Dr. John R. Horner, Dr. Donald Winston, Dr. Robert W. Fields, and Dr. Kerry Foresman. Their insight, encouragement, and editorial assistance are greatly appreciated. I would especially lik e to thank Jack Horner for the opportunity to work on his three bone beds. I also extend thanks to Pat Leiggi, Ken Carpenter, and the late Robert Makela for invaluable conversations and ideas. Robert Makela also graciously shared his time and knowledge familiarizing me with collecting dinosaurs. Dr. Greg Retallack provided assistance in understanding and in te rp re tin g paleosols, and Ed Brook, John Kruger, Pat Reynolds, and Kirsty Erickson all furnished help in the fie ld . I am very g ratefu l to Ricky Reagan and Gloria Sundquist for allowing access to their ranches. I would also like to thank Dr. James Sears, Dr. David Alt, and Scott Sampson for helpful discussions, and John Cuplin for assistance with my graphics. Lastly, I would like to thank the M.O.R. field crews; without their help none of this would have been possible. This research was partly funded by a Sigma-Xi Society grant awarded to the author and by National Science Foundation Grant No. EAR 8705986 and a John and Catherine MacArthur Foundation Fellowship, both of which were awarded to J. R. Horner. I ll TABLE OF CONTENTS PAGE ABSTRACT .......................................................................................................................... ii ACKNOWLEDGEMENTS ................................................................................................... i l l TABLE OF CONTENTS ............................................................................................... iv-v LIST OF ILLUSTRATIONS .............................................................................. v i-v ii PART ONE— INTRODUCTION ................................................................................. 1 Landslide Butte Field Area ............................................................ 6 Procedure .............................................................................................................. 8 PART TWO—TWO MEDICINE FORMATION ................................................... 11 General Geology ............................................................................................ 11 Structural Setting ................................................................................... 14 Stratigraphy and Sedimentology ................................................ 16 Paleogeography ............................................................................................... 25 Paleoclimate ..................................................................................................... 28 PART THREE--TAPHONOMIC DATA .................................................................. 33 CANYON BONE BED ............................................................................................. 38 GEOLOGIC DATA-- Stratigraphy, Sedimentology, and Depositional Environment ................................. 38 Physical and Chemical Modifications ........................ 40 BIOLOGIC DATA-- Biologic Constraints ..................................................................... 44 Biologic Modifications ............................................................... 44 1 V LIST OF ILLUSTRATIONS FIGURE.............................................................................................................................................PAGE 1. Location Map, Landslide Butte Field Area ........................ 7 2. Generalized Outcrop Map, Two Medicine Formation ........................................................................................................... 12 3. Montana Group Stratigraphy, Northwestern and North-Central Montana ........................................................................ 14 4. Fence Diagram Illu s tra tin g S tratigraphie Relationships of the Two Medicine Formation ... 17 5. Photograph of Two Red Horizons in the Landslide Butte Field Area ...................................................................................... 21 6. Photograph of a Typical Sandstone Channel Deposit in the Landslide Butte Field Area ............ 23 7. Photograph of Root Casts and Burrows on the Uppermost Surface of a Landslide Butte Paleo-channel ..............................................................................................