Journal of Systematic Palaeontology 6 (1): 1–40 Issued 22 February 2008 doi:10.1017/S1477201907002271 Printed in the United Kingdom C The Natural History Museum The phylogeny of the ornithischian dinosaurs RichardJ.Butler∗ Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK & Department of Palaeontology, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK Paul Upchurch† Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK David B. Norman‡ Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK SYNOPSIS Ornithischia is a familiar and diverse clade of dinosaurs whose global phylogeny has remained largely unaltered since early cladistic analyses in the mid 1980s. Current understanding of ornithischian evolution is hampered by a paucity of explicitly numerical phylogenetic analyses that consider the entire clade. As a result, it is difficult to assess the robustness of current phylogenetic hypotheses for Ornithischia and the effect that the addition of new taxa or characters is likely to have on the overall topology of the clade. The new phylogenetic analysis presented here incorporates a range of new basal taxa and charac- ters in an attempt to rigorously test global ornithischian phylogeny. Parsimony analysis is carried out with 46 taxa and 221 characters. Although the strict component consensus tree shows poor resolution in a number of areas, application of reduced consensus methods provides a well-resolved picture of ornithischian interrelationships. Surprisingly, Heterodontosauridae is placed as the most basal group of all well-known ornithischians, phylogenetically distant from a stem-defined Ornithopoda, creating a topology that is more congruent with the known ornithischian stratigraphical record. There is no evidence for a monophyletic ‘Fabrosauridae’, and Lesothosaurus (the best-known ‘fabrosaur’) occupies an unusual position as the most basal member of Thyreophora. Other relationships within Thyreophora remain largely stable. The primitive thyreophoran Scelidosaurus is the sister taxon of Eurypoda (stegosaurs and ankylosaurs), rather than a basal ankylosaur as implied by some previous studies. The taxonomic content of Ornithopoda differs significantly from previous analyses and basal relationships within the clade are weakly supported, requiring further investigation. ‘Hypsilopho- dontidae’ is paraphyletic, with some taxa (Agilisaurus, Hexinlusaurus, Othnielia) placed outside of Ornithopoda as non-cerapodans. Ceratopsia and Pachycephalosauria are monophyletic and are united as Marginocephalia; however, the stability of these clades is reduced by a number of poorly preserved basal taxa. This analysis reaffirms much of the currently accepted ornithischian topology. Nevertheless, in- stability in the position and content of several clades (notably Heterodontosauridae and Ornithopoda) indicates that considerable future work on ornithischian phylogeny is required and causes problems for several current phylogenetic definitions. KEY WORDS vertebrate palaeontology, Ornithischia, systematics, cladistics, Dinosauria Contents Introduction 1 Institutional abbreviations 2 Previous analyses of ornithischian phylogeny 2 Traditional classifications 2 Cladistic studies 3 Material and Methods 5 The aim of the analysis 5 Phylogenetic framework 5 Selection of ingroup taxa 5 ∗E-mail: [email protected]; †Email: [email protected]; ‡Email: [email protected] 2 R. J. Butler et al. Supraspecific taxa 5 Included species level taxa 7 Excluded species level taxa 11 Selection of outgroup taxa 11 Analyses 12 Search methods 12 Testing the support for relationships 12 Randomisation tests 12 Bremer support 12 Bootstrapping 14 Results 16 Ornithischian monophyly 16 Pisanosaurus mertii 17 Heterodontosauridae 17 ‘Fabrosaurids’ 18 Thyreophora 19 Basal neornithischians 19 Ornithopoda 20 Hypsilophodontidae 20 Marginocephalia 21 Ceratopsia 21 Pachycephalosauria 22 Conclusions 22 Stability, instability, and future directions in ornithischian phylogeny 22 Implications for phylogenetic taxonomy of Ornithischia 22 Acknowledgements 23 References 23 Appendix 1 – Specimens and references used for coding operational taxonomic units 29 Appendix 2 – Character list 30 Appendix 3 – Data matrix 35 Appendix 4 – Tree descriptions 40 Introduction tebrate faunas are dominated by saurischians (Weishampel et al. 2004b). Ornithischians became much more abundant during the Late Jurassic and Early Cretaceous and ornith- The clade Ornithischia represents a major grouping within ischian diversity peaked during the Campanian stage of the Dinosauria, the most familiar and widely popularised of Late Cretaceous. Late Triassic–Early Jurassic ornithischians all extinct organisms. An ornithischian, Iguanodon Mantell, were generally small-bodied (1–2 m in length) bipedal curs- 1825, was the second dinosaur genus to be named, while ors (e.g. Lesothosaurus diagnosticus: Thulborn 1972; Sereno of the three taxa explicitly included within Dinosauria by 1991a), but during the rest of the Mesozoic they diversified Owen (1842), two (Iguanodon and Hylaeosaurus) were later into a considerable range of morphologies and sizes, with recognised as ornithischians. Since these early discoveries, a many groups reverting to quadrupedality. The vast majority large number of genera and species of ornithischians have of ornithischians are believed to have been herbivorous, al- been named: a recent review (Weishampel et al. 2004a) though some basal forms have been interpreted as potentially recognised over 180 valid genera. The earliest ornithischi- omnivorous (Barrett 2000). ans are known from the Carnian stage of the Late Trias- One major problem in understanding ornithischian sic (Casamiquela 1967) and the clade disappeared in the evolution is that, to date, there are few published numer- mass extinctions at the end of the Cretaceous. During this ical phylogenetic analyses dedicated solely to Ornithischia time ornithischians achieved a global distribution and are (Weishampel 2004). It is difficult, therefore, to assess the re- now known from every continent, including Antarctica (e.g. lative phylogenetic support for ornithischian clades, to look Hooker et al. 1991; Weishampel et al. 2004b). at the effects upon phylogenetic results of adding or deleting Ornithischians appear to have been extremely scarce taxa or characters, or to test alternative hypotheses of taxon during the Late Triassic (Sereno 1997) and remained un- or character evolution. Here, we present a new phylogen- common (although apparently more diverse) during the Early etic analysis of Ornithischia, as part of an on-going study of and Middle Jurassic; during this time interval terrestrial ver- ornithischian phylogeny. Phylogeny of ornithischian dinosaurs 3 Institutional abbreviations ZDM = Zigong Dinosaur Museum, Dashanpu, People’s Republic of China BMNH = Natural History Museum, London, UK ZPAL = Institute of Paleobiology of the Polish BRSMG = Bristol City Museum and Art Gallery, Bris- Academy of Sciences, Warsaw, Poland. tol, UK BP = Bernard Price Institute for Palaeontological Research, Johannesburg, South Africa BYU = Earth Science Museum, Brigham Young Previous analyses of University, Provo, Utah, USA ornithischian phylogeny CAMSM = Sedgwick Museum, University of Cam- bridge, Cambridge, UK Traditional classifications CEUM = Prehistoric Museum, College of Eastern Utah, Price, Utah, USA Although material from the clade began to be described and CV = Chongqing Natural History Museum, named in the early 19th century (Mantell 1822, 1825, 1833), Chongqing, People’s Republic of China the recognition that ornithischians formed a grouping dis- GCC = Museum of the Chendgu University of tinct from other reptiles (including other dinosaurs) was not Technology (formerly Chendgu College of reached until the work of Seeley (1887). Seeley was the first Geology), Chengdu, People’s Republic of to identify and articulate a fundamental morphological dicho- China tomy within the then described dinosaurian taxa. He recog- GI = Geological Institute, Ulaanbaatar, Mongo- nised two orders, distinguished mainly on the basis of pelvic lia anatomy, that he named Ornithischia and Saurischia. Major GSM = Geological Survey Museum, Keyworth, subdivisions of Seeley’s Ornithischia (Stegosauria, Ornitho- UK poda, Ceratopsia) were identified by Marsh (1877a, 1881, GZG = Geowissenschaftliches Zentrum der Uni- 1890) and Marsh (1894) later grouped these subdivisions versitat¨ Gottingen,¨ Gottingen,¨ Germany together as the order Predentata, generally considered syn- IGCAGS = Institute of Geology, Chinese Academy onymous with Ornithischia. of Sciences, Beijing, People’s Republic of Nopcsa (1915) proposed a subdivision within Ornithis- China chia, between the bipedal, unarmoured forms (ornithopods) IVPP = Institute of Vertebrate Paleontology and and a new suborder that he named Thyreophora (compris- Paleoanthropology, Bejing ing ankylosaurs, stegosaurs and ceratopsians). The group- MCZ = Museum of Comparative Zoology, Harvard, ing Thyreophora was often ignored by later workers, but USA the name was revived by Norman (1984) and Sereno (1984, MB = Museum fur¨ Naturkunde, Berlin, Germany 1986), although its current usage (for a clade consisting of MCF-PVPH = Museo Carmen Funes, Paleontolog´ıa de all armoured ornithischians) differs somewhat from that pro- Vertebrados Plaza Huincul, Argentina posed by Nopcsa (i.e. in current usage ceratopsians are not MNA