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The Phylogeny of Ceratosauria (Dinosauria: Theropoda)

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The Phylogeny of Ceratosauria (Dinosauria: Theropoda) Journal of Systematic Palaeontology 6 (2): 183–236 Issued 23 May 2008 doi:10.1017/S1477201907002246 Printed in the United Kingdom C The Natural History Museum The Phylogeny of Ceratosauria (Dinosauria: Theropoda) Matthew T. Carrano∗ Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560 USA Scott D. Sampson Department of Geology & Geophysics and Utah Museum of Natural History, University of Utah, Salt Lake City, UT 84112 USA SYNOPSIS Recent discoveries and analyses have drawn increased attention to Ceratosauria, a taxo- nomically and morphologically diverse group of basal theropods. By the time of its first appearance in the Late Jurassic, the group was probably globally distributed. This pattern eventually gave way to a primarily Gondwanan distribution by the Late Cretaceous. Ceratosaurs are one of several focal groups for studies of Cretaceous palaeobiogeography and their often bizarre morphological develop- ments highlight their distinctiveness. Unfortunately, lack of phylogenetic resolution, shifting views of which taxa fall within Ceratosauria and minimal overlap in coverage between systematic studies, have made it difficult to explicate any of these important evolutionary patterns. Although many taxa are fragmentary, an increase in new, more complete forms has clarified much of ceratosaur anatomy, allowed the identification of additional materials and increased our ability to compare specimens and taxa. We studied nearly 40 ceratosaurs from the Late Jurassic–Late Cretaceous of North and South America, Europe, Africa, India and Madagascar, ultimately selecting 18 for a new cladistic analysis. The results suggest that Elaphrosaurus and its relatives are the most basal ceratosaurs, followed by Ceratosaurus and Noasauridae + Abelisauridae (= Abelisauroidea). Several additional forms were identified as noasaurids, including Genusaurus. Within Abelisauridae, our analysis reveals a clade including Majungasaurus and the Indian forms, as well as a more weakly supported clade comprising Carnotaurus and Ilokelesia. These results greatly clarify the sequence of character acquisition lead- ing to, and within, Abelisauroidea. Thanks to new noasaurid materials (particularly Masiakasaurus), numerous formerly ambiguous characters can now be resolved as either abelisaurid, noasaurid or abelisauroid synapomorphies. Skull and forelimb shortening, for example, now appear to be features confined to Abelisauridae. Nevertheless, a great deal of phylogenetic resolution is lacking, particu- larly among noasaurids, which hampers attempts to glean meaningful biogeographical information from the phylogeny. As a result, temporal and geographical sampling biases are probably contributing to the apparent patterns in the data and we suggest that definitive answers must await new discover- ies. None of the recent ceratosaurian discoveries bear directly on the controversy surrounding latest Cretaceous ceratosaur biogeography. KEY WORDS systematics, dinosaur, Saurischia, evolution, Abelisauroidea, Abelisauridae, Noasaur- idae, biogeography, morphology Contents Introduction 185 Historical background 185 Constituency and placement of Ceratosauria 185 Ingroup relationships of Ceratosauria 187 Materials and methods 187 Outgroup relationships 187 Operational taxonomic units 190 Institutional abbreviations 190 Abelisaurus comahuensis Bonaparte & Novas, 1985 190 Aucasaurus garridoi Coria et al., 2002 191 Carnotaurus sastrei Bonaparte, 1985 191 Ceratosaurus nasicornis Marsh, 1884a 192 Deltadromeus agilis Sereno et al., 1996 192 Elaphrosaurus bambergi Janensch, 1920 193 ∗E-mail address: [email protected]. 184 Matthew T. Carrano and Scott D. Sampson Ekrixinatosaurus novasi Calvo et al., 2004 193 Genusaurus sisteronis Accarie et al., 1995 194 Ilokelesia aguadagrandensis Coria & Salgado, 2000 194 Indosaurus matleyi Huene & Matley, 1933 195 Laevisuchus indicus Huene & Matley, 1933 195 Majungasaurus crenatissimus (Deperet,´ 1896) Lavocat, 1955 195 Masiakasaurus knopfleri Sampson et al., 2001 196 Noasaurus leali Bonaparte & Powell, 1980 196 Rajasaurus narmadensis Wilson et al., 2003 197 Rugops primus Sereno et al., 2004 197 Spinostropheus gautieri (Lapparent, 1960) Sereno et al., 2004 197 Velocisaurus unicus Bonaparte, 1991b 198 Characters 198 Phylogenetic methods 198 Biogeographical methods 198 Results 199 Phylogenetic results 199 Biogeographical results 199 Discussion 200 Comparisons with previous analyses 200 Basal taxa 200 Deltadromeus 201 Noasauridae 201 Abelisauridae 202 Fragmentary taxa 202 Betasuchus bredai (Seeley, 1883) Huene, 1932 202 Coeluroides largus Huene & Matley, 1933 202 Compsosuchus solus Huene & Matley, 1933 202 Dryptosauroides grandis Huene & Matley, 1933 202 Genyodectes serus Woodward, 1901 202 Indosuchus raptorius Huene & Matley, 1933 207 Jubbulpuria tenuis Huene & Matley, 1933 208 Lametasaurus indicus Matley, 1924 208 Ligabueino andesi Bonaparte, 1996 208 Ornithomimoides mobilis Huene & Matley, 1933 208 Ornithomimoides? barasimlensis Huene & Matley, 1933 208 Pycnonemosaurus nevesi Kellner & Campos, 2002 208 Quilmesaurus curriei Coria, 2001 208 Tarascosaurus salluvicus Le Loeuff & Buffetaut, 1991 209 Xenotarsosaurus bonapartei Mart´ınez et al., 1986 209 South American, Cretaceous abelisauroids 209 Tendaguru ceratosaurs 209 European abelisauroids 210 North African, medial Cretaceous abelisauroids 210 North African, Late Cretaceous abelisauroids 210 Evolutionary Implications 210 Morphology 210 Biogeography 212 Stratigraphical fit 214 Persistent problems 214 Conclusions 214 Acknowledgements 215 References 215 Appendix 1. List of characters 220 Appendix 2. Taxon-by-character matrix for the 21 taxa used in this study 234 The Phylogeny of Ceratosauria (Dinosauria: Theropoda) 185 Appendix 3. Theropod specimens examined 235 Supplementary Data 236 Introduction taxon – indeed, a single specimen – from the Upper Jurassic Morrison Formation of Colorado, Ceratosaurus nasicornis. In 1999, we began an extensive phylogenetic study of Thero- Marsh noted certain characteristics of Ceratosaurus (fused poda (Dinosauria: Saurischia), to elucidate the detailed inter- pelvic elements, a coossified metatarsus: Marsh 1884c)that relationships of the basal (i.e. non-coelurosaurian) members were then unknown elsewhere among theropods, but were of this clade. In the intervening years, this task has involved also found in birds. Other features (midline dorsal osteo- firsthand examination of hundreds of specimens representing derms, a median nasal horn) were apparently unique. Cerato- more than 70 taxa and the critical review of more than 600 saurus seemed to occupy a distinct position among theropods published characters and character state observations. The that deserved formal recognition and, therefore, he set it apart results of our broader study are now in preparation and will from taxa such as Allosaurus, Megalosaurus and the ‘coe- be published elsewhere. In this paper, we focus on the phylo- lurosaurs’ in its own infraorder, Ceratosauria (Marsh 1884b). geny of Ceratosauria, particularly the primarily Gondwanan Later, the group was informally allied with Ornithomimidae radiations of the families Abelisauridae and Noasauridae. (Marsh 1892). Most previous systematic studies of Ceratosauria (e.g. For nearly half a century thereafter, the distinctiveness Coria & Salgado 2000; Coria et al. 2002; Lamanna et al. of Ceratosaurus among theropods was either explicitly or im- 2002; Wilson et al. 2003) have focused on the placement plicitly supported (e.g. Gilmore 1920). When Huene (1914, of individual – usually new – taxa. As such, they typically 1923, 1926) formally reorganised Theropoda into two largely employ relatively complete taxa with the goal of achieving size-based suborders (Coelurosauria and Carnosauria), he the greatest possible resolution. By contrast, other works specifically exempted both Tyrannosaurus and Ceratosaurus (e.g. Novas 1997; Tykoski & Rowe 2004) have attempted from ‘typical’ positions among the other large carnosaurs (al- to resolve relationships within ceratosaurs as a whole. Not though citing different reasons for each). He allied Cerato- surprisingly (see below), the latter studies tend to achieve saurus with the smaller Proceratosaurus bradleyi from the more limited resolution, with rather less agreement between Bathonian Great Oolite of England, based on the supposed them. presence of a nasal ‘horn’ in the latter. This relationship Much of the problem stems from the highly incomplete was recently supported by Madsen & Welles (2000), but has nature of many ceratosaur taxa, resulting in generally poor been questioned by most other workers (Paul 1988a, b; Holtz resolution and/or the tendency of researchers to exclude nu- 2000; Rauhut 2000, 2003). merous taxa. In addition, discrepancies can arise when stud- Very few additional taxa have been referred to Cer- ies employ different taxon samples, using only a stable core atosauria sensu Marsh, 1884b. Among these were the frag- group to which selected taxa of interest are added. This paper mentary materials described as Ceratosaurus (?) roech- attempts to alleviate several of these difficulties by presenting lingi (Kimmeridgian–Tithonian, Tendaguru Beds, Tanzania: a character and taxon-rich analysis of ceratosaur theropods, Janensch 1925) and Chienkosaurus ceratosauroides which is then analysed in several different iterations. (Tithonian, Kyangyuan Series, China: Young 1942). Other We begin with the presumption, supported in several poorly known species (e.g. Megalosaurus
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