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Two New Archosaur Reptiles from the Late Triassic Of TWO NEW ARCHOSAUR REPTILES FROM THE LATE TRIASSIC OF TEXAS by MOMCHIL NIKOLAEV ATANASSOV, M.S. A DISSERTATION IN GEOSCIENCE Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Approved Chairperson of the Qbmmittee Accepted Dean of the Graduate School August, 2002 Copyright 2002, Momchil Nikolaev Atanassov ACKNOWLEDGMENTS I would like to thank the members of my committee. Dr. James Barrick, Dr. Thomas Lehman, Dr. Richard Strauss, and the committee chairman. Dr. Sankar Chatterjee for their guidance, help, and support during the completion of this dissertation. In particular, I would like to express my gratitude to my dissertation advisor Sankar Chatterjee, who invited me to come to Texas Tech University, offered his generous hospitality, and provided valuable advice and guidance throughout this project. I also wish to thank my fellow students and colleagues Alan Coulson, Axel Hungerbiihler, Richard Kissel, Jeffrey Martz, Kyle McQuilkin, Bill Mueller, Eric Simpson, Jonathan Wagner, and Jonathan Weinbaum for many useful discussions and their help in the field and in the lab. A special thanks goes to Mariana Ivanova for her help in the field and especially for her skillful preparation of a significant amotmt of material from the Dockum Group, a tedious and time-consuming task. Bill Mueller from the Museum of Texas Tech University took most photographs with great skill and patience. I theink the Museum of Texas Tech University for allowing unlimited access to the fossil collections and the museum facilities, and the Department of Geosciences at Texas Tech University for the material support throughout my studies. I also wish to thank all the individuals who helped me during my various stays at their institutions. I thank Silvio Renesto from Dipartimento di Scienze della Terra, Universita degli Studi in Milan; Ana Paganoni and the staff at Museo Civico di Scienze Naturali in Bergamo; and Guiseppe Muscio and Fabio Dalla Vecchia from Museo Friulano di Storia Naturale in Udine for their generous hospitality and help, which made my stay in Italy enjoyable and productive. I also thank Tim Rowe, Pamela Owen, Wann Langston, Jr., Ernest Lundelius, Jr., and Ron Tykoski at the Vertebrate Paleontology Lab of University of Texas, Austin, who allowed unlimited access to their Late Triassic collections and were very helpful with information and discussions. Peter Reser from the New Mexico Museum of Natural History and Science in Albuquerque provided access to the fossil collections of the museum. The staff at Institute de Geologia at Universidad Nacional Autonoma de Mexico in Mexico City also provided unlimited access to the material of the Early Jurassic pterosaur Dimorphodon weintraubi under their care. ni TABLE OF CONTENTS ACKNOWLEDGMENTS ii ABSTRACT v LIST OF TABLES vii LIST OF FIGURES viii CHAPTER I. INTRODUCTION 1 II. GEOLOGIC SETTING 5 III. DESCRIPTION OF THE NEW ARCHOSAUR PTEROMIMIMUS 17 IV. DESCRIPTION OF THE NEW ARCnOS,A\]R PROCOELOSAURUS ....65 V. PHYLOGENETIC ANALYSIS 118 REFERENCES 147 APPENDIX A. LIST OF CHARACTERS USED IN PREVIOUS PHYLOGENETIC ANALYSES OF ARCHOSAUROMORPHA 157 B. CHARACTER MATRIX USED IN PHYLOGENETIC ANALYSIS 346 C. PHOTOGRAPHS OF PTEROMIMUS LONGICOLLIS AND PROCOELOSAURUS BREVICOLLIS 352 IV ABSTRACT Two new basal archosaurs, Pteromimus longicollis and Procoelosaurus brevicollis are described from the Tecovas Formation (late Camian) and the Cooper Canyon Formation (early Norian) of the Dockum Group of West Texas. Pteromimus is based on an incomplete skull and associated and isolated skull and vertebral elements. The skull is high, with narrow snout, large orbit and naris, pneumatized maxilla and premaxilla, large inflated frontal, short parietal, plate-like supraoccipital, and reduced post-temporal openings. The dentition is thecodont and consists of conical teeth with fluted apices. The premaxillary teeth are long and slightly recurved, and the maxillary teeth are short and more laterally compressed. The vertebrae of both Pteromimus and Procoelosaurus £ire with procoelous and hollow centra, with large cavities for the interspinal ligament, well-developed epipophyses, and long and low neural arches carrying long neural processes v«th spine tables. Pteromimus is distinguished by low neural processes with weakly developed spine tables and ornamentation, while Procoelosaurus is characterized by higher neural processes that expand into wide spine tables with distinctive sculpturing. The cervical vertebrae of Pteromimus are elongate, dorsoventrally compressed, and bear unusual rib articulations consisting of a large posterior depression and a small anterior process. Procoelosaurus is represented by an association of vertebrae, pelvis, hindlimb and skull elements, and by a large number of isolated vertebrae. The maxilla and dentary of Procoelosaurus bear numerous teeth with thecodont implantation and crowns that are recurved, laterally compressed, and serrated. Procoelosaurus has at least three sacral vertebrae, large plate-like ischium, and ilium with a low blade, reduced preacetabular process, and a long, tapering postacetabular process. The femur appears similar to those of pterosaurs with anteriorly bowed shaft, well developed condyles, and an intumed head. The ankle and foot of Procoelosaurus are similar to those of early pterosaurs with an advanced mesotarsal tarsus, hooked fifth metatarsal, and closely appressed metatarsals I-IV subequal in length and indicating a plantigrade pes. A phylogenetic analysis of Archosauromorpha indicates that the two new reptiles and pterosaurs are omithodiran archosaurs and form a monophyletic clade that is the sister-group to Scleromochlus + Dinosauromorpha. Pteromimus is the sister- group of pterosaurs, and Procoelosaurus is the sister-group to the clade Pteromimus + Pterosauria. VI LIST OF TABLES 1. Measurements of the vertebrae of Pteromimus longicollis 45 2. Measurements of the vertebrae of Procoelosaurus brevicollis 93 3. Ratios of iliac blade height to acetabulum height in basal archosauriforms 107 4. Character matrix used in phylogenetic analysis 347 Vll LIST OF FIGURES 1. Generalized geologic map of the southern High Plains region of West Texas and eastern New Mexico, showing distribution of the Upper Triassic Dockum Group 14 2. Detailed geologic map of the Dockum Group in the upper Brazos and Colorado River Valleys in West Texas, showing the fossil localities 15 3. Stratigraphy of the Dockum Group at the Post Quarry, Garza County, and the Kirkpatrick Quarry, Crosby County, Texas 16 4. Quarry map of the type material (skull association) of Pteromimus longicollis at Post Quarry 48 5. Lateral view of skull reconstruction of Pteromimus longicollis 49 6. Dorsal view of skull restorations of P/erow/wM5'/o«g/co//w 50 7. Posterior view of skull restoration of Pteromimus longicollis 51 8. Lateral, medial, anterior and posterior view of premaxilla of Pteromimus longicollis 52 9. Lateral and medial view of the maxillae of Pteromimus longicollis 53 10. Dorsal and ventral view of nasal of Pteromimus longicollis 54 U. Lateral view of partially preserved skull of Pteromimus longicollis 55 12. Anterior view of partially preserved skull of Pteromimus longicollis 56 viii 13. Dorsolateral view of prefrontal-postfrontal association of Pteromimus longicollis 57 14. Lateral and medial views of postorbital of Pteromimus longicollis 58 15. Medial and lateroposterior views of the right quadrate of Pteromimus longicollis with fragments of the quadratojugal and squamosal attached 59 16. Dorsal and ventral views of reconstructed palate of Pteromimus longicollis 60 17. Lateral and medial views of anterior dentary of Pteromimus longicollis 61 18. Dorsal, lateral, anterior and posterior views of the mid-cervical vertebra TTUP 10081/2 of Pteromimus longicollis 62 19. Lateral, dorsal, anterior and posterior views of the anterior cervical vertebra TTUP 10088 of Pteromimus longicollis 63 20. Lateral, anterior, posterior, and oblique views of the large cervical vertebra of Pteromimus longicollis 64 21. Lateral and medial views of the maxilla of Procoelosaurus brevicollis 108 22. Lateral and medial view of dentary of Procoelosaurus brevicollis 109 23. Anterior cervical of Procoelosaurus brevicollis in all views 110 24. Dorsal vertebra of Procoelosaurus brevicollis in all views Ill 25. Lateral and medial view of ilium of Pracoe/o5flMrw5 6revzco//w 112 ix 26. Lateral view of two ischia (TTUP 10108/3 and 10109) of Procoelosaurus brevicollis 113 27, Anterior and posterior view of femur of Procoelosaurus brevicollis 114 28. Anterior wievi of i\h\didcndif\h\x\di of Procoelosaurus brevicollis 115 29. Proximal and distal views of astragalus and calcaneum of Procoelosaurus brevicollis 116 30. Anterior and posterior views of pes of Procoelosaurus brevicollis 117 31. Majority-rule consensus tree of Archosauromorpha with Lepidosauromorpha as an outgroup 146 CHAPTER I INTRODUCTION General Background of Study The continental red beds of the Late Triassic Dockum Group are widely exposed along the foot of the Caprock Escarpment of the Southern High Plains in western Texas, through the Canadian River Valley in Texas and eastern New Mexico, and along the Pecos River Valley in New Mexico and southward into Texas. The Dockum Group rests unconformably on Permian strata, and is unconformably overlain by Cretaceous, Tertiary, or Quaternary strata. The Triassic deposits have been studied by stratigraphers, sedimentologists, and paleontologists
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