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Description of Tanytrachelos Ahynis and Its Implications for the Phylogeny of Protorosauria

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Description of Tanytrachelos Ahynis and Its Implications for the Phylogeny of Protorosauria Description of Tanytrachelos ahynis and its implications for the phylogeny of Protorosauria Amy C. Smith Dissertation submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Geosciences Michał Kowalewski, Chair Nicholas Fraser, Co-chair Alton Dooley Kenneth Eriksson Shuhai Xiao April 11, 2011, Blacksburg, Virginia Keywords: Protorosaurs, Archosauromorphs, Cladistics, Quantitative Morphometrics Description of Tanytrachelos ahynis and its implications for the phylogeny of Protorosauria Amy C. Smith ABSTRACT Tanytrachelos ahynis, a small (21 cm long) aquatic protorosaur from the Upper Triassic sediments in the Cow Branch Formation of the Newark Supergroup, has been briefly described in 1979 by P. E. Olsen. A growing addition of nearly 200 specimens and the availability of CT imaging allow for an extensively detailed redescription. This redescription fills in missing data in cladistic analyses of Protorosauria, allowing for protorosaur monophyly to be retested with a more robust data set. Two hundred and ninety specimens and two CT scans of specimens were examined, with seventy linear measurements, four angular measurements, and five derived variables comprising the quantitative observations. These qualitative and quantitative observations then provided data for Tanytrachelos in two cladistic analyses of Protorosauria. The first analysis included the outgroup Petrolacosaurus, twenty-one protorosaurs, and nine other archosauromorphs. The second analysis included the twenty taxa within this sample that had a data completeness of 50% or higher. Diagnostic qualities of Tanytrachelos include large orbits (11% - 13% the lateral area of the skull), a fused axis and atlas, a tail that spans half the vertebral length, and paired curved heterotopic bones in some specimens (a sign of sexual dimorphism). The disparity of size between the hind and fore limbs, as well as traces of soft tissue, suggest that Tanytrachelos propelled through the water with its back legs. This taxon is similar to Gwyneddosaurus, found in the Lockatong Formation (Newark Supergroup) in Montgomery County, PA, but should maintain its generic name due to lack of diagnostic qualities for Gwyneddosaurus. With the new observations of Tanytrachelos included, each of the two cladistic analyses yielded a single most parsimonious tree presenting a paraphyletic Protorosauria. Both results placed Prolacerta within the confines of Protorosauria, in contrast with the previous suggestion by three publications that Prolacerta was not a true protorosaur. The analysis of all taxa presented Boreopricea as the most basal protorosaur, while the analysis of the twenty most complete taxa presented Protorosaurus as most primitive. Neither tree fully agrees with any previously published data, partly due to differences in taxa sampling between studies. Dedicated to my loving husband, whose unfaltering support helped me succeed in the face of hardship at Virginia Tech. iii ACKNOWLEDGEMENTS The author would like to thank M. Kowalewski of the Virginia Polytechnic Institute and State University (Blacksburg) for help with morphometric methods, assistance with SAS, and project and academic guidance, A. Dooley of the Virginia Museum of Natural History (Martinsville) and N. Fraser of the National Museum of Scotland (Edinburgh) for access to specimen collections and for project guidance, and S. Xiao and K. Eriksson of the Virginia Polytechnic Institute and State University for project and academic guidance. The author is also grateful for the help from J. Barringer and Y. Tulu of Michigan State University (East Lansing), and S. Godfrey of the Calvert Marine Museum (Solomons, MD), who provided the author with invaluable feedback and support. The author thanks M. Lemon of the Virginia Polytechnic Institute and State University for assistance with printing the poster resulting from this study. This project was funded by the Tillman Geosciences Graduate Research Award (2008, Virginia Tech) and the D.R. Wones Research Award (2009, Virginia Tech). iv TABLE OF CONTENTS LIST OF FIGURES……………………………………………………………………...vii LIST OF TABLES…………………………………………………………………..……ix INTRODUCTION……………………..……………………………………………….…1 A morphological and morphometric redescription of Tanytrachelos ahynis……………..2 ABSTRACT……………………………………………………………………….2 INTRODUCTION………………………………………………………………...3 The Newark Supergroup and the Dan River Basin………………………..3 The Cow Branch Formation of the Dan River Group….………………….4 Tanytrachelos Locality within the Dan River Basin...…………………….4 Previous Work on Tanytrachelos………………………………………….6 MATERIALS AND METHODS………………………………………………….8 Specimens Studied……………………………………………………...…8 Photograph Acquisition…………………………………………………...8 Contrast Enhancement in Photographs……………………………………8 Gathering Qualitative Data………………………………………………10 Gathering Quantitative Data…………………………………………..…10 RESULTS……………………………………………………………………….13 Skull …………………………………………………………………….14 Vertebral Column and Ribs ……………………………………………..17 Pectoral Girdle and Anterior Limbs …………………………………….26 Pelvic Girdle and Posterior Limbs ………………………………………30 Gastralia and Heterotopic Bones ………………………………………..34 Soft Tissue Traces ……………………………………………………….37 Specimens with Noticeably Wide Bodies………………………………..39 Juvenile Specimens of Tantrachelos…………………….………………39 Quantitative Results……….…………………………………….……….41 DISCUSSION……………………………………………………………………47 Diagnostic Qualities of Tanytrachelos …………………………………..47 Possible Function of Paired Heterotopic Bones………………………….47 The Relationship of Gwyneddosaurus to Tanytrachelos………………...48 Locomotion of Tanytrachelos…………………………………………....51 The Possibility of Neoteny in Tanytrachelos…………………………….52 Comparison and Contrast between Tanytrachelos and its proposed sister taxon Tanystropheus…………………………………………..…53 Potential Sources of Error in Morphometric Measurements…………….54 v LITERATURE CITED…………………………………………………………..55 A reanalysis of protorosaur cladistics and its impact on archosauromorph evolutionary relationships……………………………………………………………………..57 ABSTRACT…………………………………………………………………….57 INTRODUCTION…………………………………………………………….....58 Previous Studies of Protorosaur Phylogeny…………………………..58 MATERIALS AND METHODS……………………………………………….63 Taxa Selection and Character Compilation……………………………..63 Cladistic Analysis of Protorosauria…….……………………………….63 RESULTS………………………………………………………………………65 Results of the Analysis Including All Taxa…………………………….65 Results of the Analysis Including Only Taxa with 50% or Higher Data Completeness……………………………………………………66 DISCUSSION……………………………………………………….………….67 Consistencies and Inconsistencies between Both Analyses……….……67 Comparison of Results to Previous Studies……………………………..68 Possibilities for Future Work……………………………………………69 LITERATURE CITED….………………………………………………………70 SYNOPSIS………………………………………………………………………………75 APPENDICES………………….……………………………………………………….77 Appendix A: List of Tanytrachelos ahynis Specimens Studied…..……………..77 Appendix B: Morphometric Measurements of Tanytrachelos Specimen Elements…………………………………………………….…………...78 Appendix C: Characters Used in the Cladistic Analysis…………….………..…94 Appendix D: Matrix of Character States used in the Cladistic Analyses………………………………………………………………..100 vi LIST OF FIGURES FIGURE 1. Locations of the southernmost basins of the Newark Supergroup…………..3 FIGURE 2. The Solite Quarry…………………………………………………………….4 FIGURE 3. Diagrams of the Van Houten Cycles of the Solite Quarry…………………...5 FIGURE 4. Photograph of YPM7496A demonstrating the Image>Calculations function as well as the Apply Image function…………………………………………9 FIGURE 5. Photograph of VMNH120016 demonstrating the Apply Image>Multiply>Red channel adjustment………………………………….10 FIGURE 6. Linear and angle measurements taken from individual elements of Tanytrachelos………..……………………………………………………...11 FIGURE 7. The type specimen of Tanytrachelos ahynis, YPM7496……………………13 FIGURE 8. Skulls of Tanytrachelos……………………………………………………..16 FIGURE 9. Comparison of the area of the orbit to the lateral area of the skull…………17 FIGURE 10. Sequences of cervical vertebrae of Tanytrachelos……………………...…18 FIGURE 11. Articulated and disarticulated dorsal vertebrae of Tanytrachelos…………20 FIGURE 12. Articulated and disarticulated ribs of Tanytrachelos………………………22 FIGURE 13. The sacral vertebrae of Tanytrachelos…………………………………….23 FIGURE 14. Caudal vertebrae of Tanytrachelos………………………………………..26 FIGURE 15. Scapulae and coracoids of Tanytrachelos…………………………………27 FIGURE 16. The anterior limb of Tanytrachelos………………………………………..29 FIGURE 17. The right manus of Tanytrachelos…………………………………………30 FIGURE 18. The pelvic girdle of Tanytrachelos in various states of articulation………31 FIGURE 19. The right hindlimb and partial left hindlimb of Tanytrachelos……………32 FIGURE 20. Illustrations and photographs of the pes of Tanytrachelos………………..34 FIGURE 21. Sets of gastralia found in Tanytrachelos…………………………………..35 vii FIGURE 22. Heterotopic bones found in Tanytrachelos............................................…...36 FIGURE 23. Traces of soft tissue in specimens of Tanytrachelos………………………38 FIGURE 24. Specimens of Tanytrachelos that have wider ribcages than average specimens…………………………………………………………………..39 FIGURE 25. The two smallest juvenile specimens of Tanytrachelos found to date…….40 FIGURE 26. VMNH3668, the specimen of Gwyneddichnium found in the Solite Quarry……………………………………………………………………...51 FIGURE 27. The cladistic analysis of Protorosauria as presented by Benton and Allen (1997)……………………………………………………………………....59 FIGURE 28. The cladistic analysis
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