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A Phylogenetic Analysis of the Basal Ornithischia (Reptilia, Dinosauria)

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A Phylogenetic Analysis of the Basal Ornithischia (Reptilia, Dinosauria) A PHYLOGENETIC ANALYSIS OF THE BASAL ORNITHISCHIA (REPTILIA, DINOSAURIA) Marc Richard Spencer A Thesis Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements of the degree of MASTER OF SCIENCE December 2007 Committee: Margaret M. Yacobucci, Advisor Don C. Steinker Daniel M. Pavuk © 2007 Marc Richard Spencer All Rights Reserved iii ABSTRACT Margaret M. Yacobucci, Advisor The placement of Lesothosaurus diagnosticus and the Heterodontosauridae within the Ornithischia has been problematic. Historically, Lesothosaurus has been regarded as a basal ornithischian dinosaur, the sister taxon to the Genasauria. Recent phylogenetic analyses, however, have placed Lesothosaurus as a more derived ornithischian within the Genasauria. The Fabrosauridae, of which Lesothosaurus was considered a member, has never been phylogenetically corroborated and has been considered a paraphyletic assemblage. Prior to recent phylogenetic analyses, the problematic Heterodontosauridae was placed within the Ornithopoda as the sister taxon to the Euornithopoda. The heterodontosaurids have also been considered as the basal member of the Cerapoda (Ornithopoda + Marginocephalia), the sister taxon to the Marginocephalia, and as the sister taxon to the Genasauria. To reevaluate the placement of these taxa, along with other basal ornithischians and more derived subclades, a phylogenetic analysis of 19 taxonomic units, including two outgroup taxa, was performed. Analysis of 97 characters and their associated character states culled, modified, and/or rescored from published literature based on published descriptions, produced four most parsimonious trees. Consistency and retention indices were calculated and a bootstrap analysis was performed to determine the relative support for the resultant phylogeny. The Ornithischia was recovered with Pisanosaurus as its basalmost member. A monophyletic Genasauria was recovered with two major clades: Eocursor + Cerapoda and Fabrosauridae + Thyreophora. Lesothosaurus was recovered within the Fabrosauridae, along with a clade consisting of Stormbergia + Agilisaurus. iv The Heterodontosauridae was recovered as the basalmost taxon of the Cerapoda. In the bootstrap analysis, however, several taxa, including the Fabrosauridae, collapse down to form a polytomy at the base of the Genasauria consisting of Eocursor, Lesothosaurus, Stormbergia + Agilisaurus, Cerapoda, and Thyreophora. This analysis is the first to recover a weakly-supported Fabrosauridae clade, and lends further support to the placement of the Heterodontosauridae within the Cerapoda, but outside of the Ornithopoda. Additionally, the implication of the phylogenetic relationship of Eocursor and the Cerapoda indicates, paleobiogeographically, that they evolved in the southern supercontinent of Gondwana in present-day southern Africa. v This thesis is dedicated to my loving mother, Pamela Yerry, and to the memory of my loving grandfather, the late Richard Murgatroyd. Your love and guidance have made me the man that I am today and you have taught me that strength is far more than merely a physical attribute; it is a measure of character and will, how one stands up after being knocked down, and how the love of one can affect many. I am forever indebted to you both. Thank you. vi ACKNOWLEDGEMENTS A project such as this can never be completed by just one person without the help of others. For this, I am deeply grateful for the guidance and encouragement of my advisor, Dr. Peg Yacobucci. You were always willing, regardless of the time of day and how much work you had piled up, to entertain the most trivial questions, which would inevitably turn into at least half-hour discussions and, more likely, half-hour digressions. I am grateful to my committee members Dr. Don Steinker and Dr. Dan Pavuk for their patience throughout a long and arduous thesis project that began with a thesis proposal that was ultimately, as you so correctly pointed out, more along the lines of several doctoral dissertations. Dr. Richard Butler of the Natural History Museum (London) generously provided me with a copy of his 2005 data matrix regarding basal ornithischian dinosaurs. I would like to express my appreciation to the BGSU Geology Department faculty and staff for their support. To my fellow graduate students and friends in the BGSU Geology Department and, in particular, Chris Pepple, Chris Wright, and Chris Klug – you helped me through this process, perhaps unknowingly, with encouragement and, most importantly, with your company (as drinking buddies). To my family – my mother, Pam Yerry, my sister, Tracy Liuzzi, my brother-in-law, Frank Liuzzi, my brother, Scott Spencer, and my sister, Amanda Yerry – your overwhelming love and support cannot be quantified, but it can be felt and for that I am forever thankful to you all. To my friends – your support, indirectly, through your sarcastic jokes and endless mocking banter, as well as your genuine encouragement, has helped me through this project and kept me grounded. Collectively, my family and friends have all helped to make this possible, and I sincerely thank you. vii TABLE OF CONTENTS Page 1. INTRODUCTION ........................................................................................................... 1 1.1. Purpose of Study................................................................................................. 3 2. PREVIOUS WORK .......................................................................................................... 6 2.1. Phylogenetic Systematics.................................................................................... 6 2.2. Dinosauria .......................................................................................................... 8 3. REVIEW OF TAXONOMIC UNITS ............................................................................... 18 3.1. Operational Taxonomic Units ............................................................................ 18 3.1.1. Outgroup OTUs .................................................................................. 19 Marasuchus lilloensis ....................................................................... 19 Saurischia .......................................................................................... 21 3.1.2. Ingroup OTUs ..................................................................................... 24 Pisanosaurus mertii .......................................................................... 26 Eocursor parvus ................................................................................ 31 Lesothosaurus diagnosticus .............................................................. 33 Stormbergia dangershoeki ................................................................ 41 Heterodontosaurus tucki ................................................................... 43 Abrictosaurus consors ...................................................................... 47 Agilisaurus louderbacki .................................................................... 50 Hypsilophodon foxii .......................................................................... 53 Thescelosaurus neglectus .................................................................. 56 Iguanodontia ..................................................................................... 59 viii Pachycephalosauria ........................................................................... 62 Ceratopsia ......................................................................................... 65 Scutellosaurus lawleri ....................................................................... 68 Emausaurus ernsti ............................................................................ 70 Scelidosaurus harrisonii ................................................................... 72 Stegosauria ........................................................................................ 75 Ankylosauria ..................................................................................... 80 4. METHODS ........................................................................................................................ 87 4.1. Characters and Character States.......................................................................... 87 4.2. Taxon-Character Matrix ..................................................................................... 88 4.3. Phylogenetic Analysis ........................................................................................ 90 5. RESULTS ........................................................................................................................ 94 5.1. Node 1 – Ornithischia ...................................................................................... 101 5.2. Node 2 – Genasauria ........................................................................................ 102 5.3. Node 3 – Unnamed Clade (Stormbergia + Agilisaurus) ................................. 103 5.4. Node 4 – Cerapoda ........................................................................................... 104 5.5. Node 5 – Heterodontosauridae ......................................................................... 105 5.6. Node 6 – Unnamed Clade (Hypsilophodontidae + Iguanodontia + Marginocephalia) ............................................................................................. 106 5.7. Node 7 – Hypsilophodontidae ........................................................................
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