In both Ceratosaurus and Noasauridae, there is no fenestra in the antorbital fossa, though a deep fossa/sinus is present (Witmer 1997; Madsen &. Welles 2000 ...
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A RE-EVALUATION OF SEVERAL CHARACTER STATES IN NONCOELUROSAURIAN TETANURAE (DINOSAURIA: THEROPODA) WITH IMPLICATIONS FOR PHYLOGENY OF BASAL TETANURANS SORKIN, Boris, George Mason University, Science & Technology Campus, Manassas, VA, United States of America, 20110 Presented as a poster at the 2015 meeting of the Society of Vertebrate Paleontology. Recommended reference to this presentation: Sorkin, B. 2015. A re-evaluation of several character states in non-coelurosaurian Tetanurae (Dinosauria: Theropoda) with implications for phylogeny of basal tetanurans. Journal of Vertebrate Paleontology, Program and Abstracts, 2015, 217.
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ABSTRACT A majority of recent phylogenetic analyses of Tetanurae (Dinosauria: Theropoda) place basal (= non-coelurosaurian) tetanurans into clades Megalosauroidea and Allosauroidea forming successively closer outgroups to Coelurosauria. However, the positions of genera Cryolophosaurus, Sinosaurus, Monolophosaurus and Acrocanthosaurus and clade Megaraptora remain controversial and a few phylogenetic analyses question the monophyly of both Megalosauroidea and Allosauroidea. This presentation re-evaluates the phylogeny of noncoelurosaurian Tetanurae by re-examining highly distinct and size- and ecomorphologyindependent states of several characters used in previous analyses. Cryolophosaurus possesses a small lesser trochanter, indicating it is among the most basal neotheropods (Coelophysis, Dilophosaurus). Sinosaurus retains a distally expanded scapula of the most basal neotheropods but shares with Ceratosauria & Tetanurae a large lesser trochanter, suggesting that it is more derived than the former but less derived than the latter. Spinosauridae and Carcharodontosauridae (except Acrocanthosaurus and Eocarcharia) possess a lesser trochanter extending proximally to the ventral margin of femoral head and lack a maxillary fenestra, suggesting that they are the most basal tetanurans. Piatnitzkysauridae, Metriacanthosauridae, Neovenator, Megaraptora, Megalosauridae, Acrocanthosauridae (Acrocanthosaurus, Eocarcharia) and Allosauridae (Allosaurus, Saurophaganax) share with basal Coelurosauria (Zuolong, Tanycolagreus, Coelurus, Tyrannosauroidea) a lesser trochanter extending proximally to the middle of femoral head (lesser trochanter extends proximally to the dorsal margin of femoral head in Megaraptora, Tyrannosauridae, and ornithomimosaur Beishanlong). The above basal tetanurans and Monolophosaurus also share with Coelurosauria a maxillary fenestra. Megalosauridae, Monolophosaurus, Acrocanthosauridae and Allosauridae
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share with Coelurosauria a posteroventrally expanded surangular contact of dentary and a metacarpal IV less than 25% of metacarpal III or absent, forming a clade Avetheropoda. Monolophosaurus, Acrocanthosauridae and Allosauridae also share with basal Coelurosauria (Zuolong, Tanycolagreus, Tyrannosauroidea, Ornitholestes) a robust dorsal ramus of quadratojugal, forming a clade Euavetheropoda. Allosauridae share with Coelurosauria a medially open maxillary antrum (evolved independently in Metriacanthosauridae and Eocarcharia).
INTRODUCTION Theropod dinosaurs of the clade Tetanurae more basal than members of the tetanuran clade Coelurosauria dominated ecological niches of large terrestrial predators from Middle Jurassic to Early Late Cretaceous (Benson et al. 2010). Basal tetanurans included the first giant (>1 tonne) and many of the largest (≥6 tonnes) terrestrial predators, as well as giant semi-aquatic forms (Paul 2010; Ibrahim et al. 2014). Therefore, evolutionary history of these theropods is central to the understanding of ecology and biogeography of Middle Jurassic to Early Cretaceous terrestrial ecosystems and to the understanding of factors that shape the evolutionary history of terrestrial predators. The current consensus on the phylogeny of basal Tetanurae (Carrano et al. 2012; Hendrickx & Mateus 2014) is the existence of two major clades: the more basal Megalosauroidea (containing Piatnitzkysauridae, Megalosauridae and Spinosauridae) and the more derived Allosauroidea (containing Metriacanthosauridae, Carcharodontosauridae and Allosauridae) forming a clade Avetheropoda with Coelurosauria (Fig. 1).
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However, the position of a number of basal tetanuran taxa remains uncertain. Early Jurassic Cryolophosaurus and Sinosaurus (=”Dilophosaurus sinensis”; Xing (2012)) are placed outside of Tetanurae and even Ceratosauria by some analyses (Smith et al. 2007; Sues et al. 2011) but among the most basal Tetanurae by others (Carrano et al. 2012). The position of Middle Jurassic Monolophosaurus ranges from a tetanuran more basal than Megalosauroidea (Carrano et al. 2012), to one more derived than Megalosauroidea but more basal than Allosauroidea (Smith et al. 2007; Brusatte et al. 2010), to an allosauroid (Loewen et al. 2013; Porfiri et al. 2014). Early to Late Cretaceous Megaraptora are placed among Allosauroidea by Benson et al. (2010) and Carrano et al. (2012) but among Tyrannosauroidea, a clade of basal coelurosaurs, by Novas et al. (2013) and Porfiri et al. (2014). An Early Cretaceous allosauroid Acrocanthosaurus is placed among Allosauridae by Currie & Carpenter (2000) and Novas et al. (2005) but among Carcharodontosauridae by Eddy & Clarke (2011) and Carrano et al. (2012). The monophyly of Megalosauroidea was questioned by Loewen et al. (2013), who found that megalosauroids Eustreptospondylus, Piatnitzkysaurus, and Dubreuillosaurus formed successive outgroups to Avetheropoda. Lastly, Paul (1988, 2010) argued that Allosauridae (containing Allosaurus and closely related Saurophaganax known from fragmentary remains (Chure 1995)), but not Metriacanthosauridae or Carcharodontosauridae, formed a clade with Tyrannosauroidea and other basal coelurosaurs, making Allosauroidea paraphyletic.
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Figure 1. Consensus phylogeny of Neotheropoda. After Smith et al. (2007), Carrano et al. (2012), Pol & Rauhut (2012), Senter et al. (2012), Hendrickx & Mateus (2014), Lee et al. (2014).
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The purpose of this presentation is to re-evaluate the phylogeny of non-coelurosaurian Tetanurae by re-examining several characters used in previous analyses which exhibit highly distinct and size- and ecomorphology-independent states.
INSTITUTIONAL ABBREVIATIONS AODF: Australian Age of Dinosaurs Fossil; BMMS: Bürgermeister Müller Museum Solnhofen, Solnhofen; CM: Carnegie Museum of Natural History, Pittsburgh; CMI: Children’s Museum of Indianapolis, Indianapolis; CV: Chungking Museum of Natural History, Chungking; DDM: Dinosaur Discovery Museum, Kenosha; DNM-QEH: Dinosaur National Monument, Quarry Exhibit Hall, Jensen; FMNH: Field Museum of Natural History, Chicago; FPDM: Fukui Prefectural Dinosaur Museum, Katsuyama; FRDC: Fossil Research and Development Center, Third Geology and Mineral Resources Exploration Academy, Gansu Provincial Bureau of GeoExploration and Mineral Development, Lanzhou; GIN: Paleontological Center of Mongolia, Ulaan Bataar; IVPP: Institute of Palaeontology and Palaeoanthropology, Beijing; MACN-CH: Museo Argentino de Ciencias Naturales “B. Rivadavia,” Colección Chubut, Buenos Aires; MCCM: Museo de las Ciencias de Castilla-La Mancha, Cuenca; MCF-PVPH: Museo Carmen Funes, Paleontología de Vertebrados, Plaza Huincul, Neuquén; MIWG: Dinosaur Isle, Isle of Wight Museum Service, Sandown; ML: Museu da Lourinhã, Lourinhã; MMCH-Pv, Museo Municipal “Ernesto Bachmann”, Villa El Chocón, Neuquén; MNA: Museum of Northern Arizona, Flagstaff; MNHN: Muséum National d’Histoire Naturelle, Paris; MNN: Musée National du Niger, Niamey; MPEF-PV: Museo Paleontológico “Egidio Feruglio”, colección Paleontología Vertebrados, Trelew; MSC: Maryland Science Center, Baltimore; MUCP: Museo de la Universidad Nacional del Comahue, Neuquén; MU-UFRJ: Museu Nacional – UFRJ, Rio
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de Janeiro; MWC: Museum of Western Colorado, Fruita; NCSM: North Carolina Museum of Natural Sciences, Raleigh; NHM: Natural History Museum, London; OUMNH: Oxford University Museum of Natural History, Oxford; PULR: Paleontología, Universidad Nacional de La Rioja, La Rioja; PVL: Fundación Miguel Lillo, Universidad Nacional de Tucumán, San Miguel de Tucumán; RTMP: Royal Tyrrell Museum of Paleontology, Drumheller; SGM: Ministére de l’Énergie et des Mines, Rabat; SMNS: Staatliches Museum für Naturkunde, Stuttgart; SMU: Southern Methodist University, Dallas; TPII: Thanksgiving Point Institute, Inc. (North American Museum of Ancient Life), Lehi; UCMP: University of California Museum of Paleontology, Berkeley; USNM: National Museum of Natural History, Smithsonian Institution, Washington; UUVP: Utah Museum of Natural History, University of Utah, Salt Lake City; ZDM: Zigong Dinosaur Museum, Zigong; ZLJ: Lufeng World Dinosaur Valley Park, Yunnan; ZPAL: Palaeozoological Institute, Polish Academy of Sciences, Warsaw.
MATERIALS & METHODS States of the characters being examined are illustrated by figures produced by editing figures from previous publications, images available online, or digital photographs taken by the author using Adobe Photoshop 7.0. Ceratosauria (containing Ceratosaurus and Abelisauroidea) and more basal neotheropods Coelophysis (=Syntarsus; Bristowe & Raath (2004)), Dilophosaurus and Zupaysaurus (which form a clade Coelophysoidea according to Ezcurra & Novas (2007), Martinez et al. (2011) and Carrano et al. (2012)) are used as outgroups to Tetanurae, there being a strong consensus on the phylogenetic relationship of these taxa (Ezcurra & Novas 2007; Smith et al. 2007; Sues et al. 2011; Carrano et al. 2012; Pol & Rauhut 2012; Fig. 1). There is also a strong consensus that Coelurosauria are more derived than any of the tetanurans discussed in the Introduction, that Tyrannosauroidea and Zuolong, Tanycolagreus,
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Coelurus and Ornitholestes are the most basal coelurosaurs and that Compsognathidae are more derived, forming a sister group to coelurosaurian clade Maniraptoriformes (containing Ornithomimosauria and Maniraptora) (Senter et al. 2012; Lee et al. 2014; Fig. 1). Because of the small number of characters examined, a quantitative phylogenetic analysis was not performed. Instead, the distribution of character states among Neotheropoda is described separately for each character in the Results. The implications of this character state distribution for the phylogeny of non-coelurosaurian Tetanurae are then discussed in the Discussion.
RESULTS Maxillary antrum and associated fenestrae In the most basal theropods Eodromaeus and Herrerasaurus there is a single small opening near the anterior margin of antorbital fossa of the maxilla, considered homologous with the promaxillary fenestra of Allosaurus and Coelurosauria (Witmer 1997; Martinez et al. 2011). This opening is absent in the basal neotheropods Tawa and Coelophysis (Rowe, 1989; Witmer 1997; Martinez et al. 2011; Fig. 2A), suggesting its loss is a synapomorphy of Neotheropoda. However, a similar opening is present in basal neotheropods Dilophosaurus and Zupaysaurus (Witmer 1997; Ezcurra & Novas 2007; Fig. 2B). In both Ceratosaurus and Noasauridae, there is no fenestra in the antorbital fossa, though a deep fossa/sinus is present (Witmer 1997; Madsen & Welles 2000; Carrano et al. 2002; Fig. 2D, E). This suggests that the small fenestra in the antorbital fossa of Abelisauridae (Witmer 1997; Fig. 2F) had evolved independently from that of Eodromaeus, Herrerasaurus, Dilophosaurus and Zupaysaurus and the absence of a fenestra in the antorbital fossa of the maxilla is plesiomorphic for Tetanurae. In all of the above taxa, a
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cavity within the ascending ramus of the maxilla, when present, is enclosed by bone medially (Witmer 1997). In contrast, Allosaurus and basal Coelurosauria (Zuolong, Tyrannosauroidea, unknown in Tanycolagreus) possess a maxillary antrum (cavity) that is open medially. The base of ascending ramus of the maxilla is pierced by two fenestrae. The larger maxillary fenestra (diameter ≥ 20% of anteroposterior width of ascending maxillary ramus at the fenestra) lies immediately anterior to pila postantralis (postantral strut) visible in medial view. Its path is roughly perpendicular to the lateral surface of the maxilla. The much smaller promaxillary fenestra lies anterior to the maxillary one. Its path in many taxa is oblique or parallel to the lateral surface of maxilla, obscuring the promaxillary fenestra in lateral view. (Witmer 1997; Fig. 2U, V, W). Maxillary antrum is also medially open in compsognathids Compsognathus and Sinosauropteryx (Chiappe & Göhlich 2010, fig. 9), confirming that this condition was present in the common ancestor of Coelurosauria and making the medially enclosed maxillary antrum of Ornitholestes (Witmer 1997) a secondary reversal. There appears to be no fenestra in the antorbital fossa of the maxilla in spinosaurids Suchomimus and Irritator (Sereno et al. 1998; Sues et al. 2002; Fig. 2G, H). Carrano et al. (2012) argued that a canal extending into the anterior ramus of maxilla in Spinosauridae and Megalosauridae is a derived form of promaxillary fenestra (character 27, state 2). The author was unable to evaluate this interpretation because of lack of access to specimens. However, as argued below, the homology between a single small fenestra present in the antorbital fossa of some non-coelurosaur tetanurans and the promaxillary fenestra of Allosaurus and Coelurosauria is questionable.
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Carcharodontosaurid Carcharodontosaurus possesses a single small fenestra in the antorbital fossa (Brusatte & Sereno 2007; Fig. 2I). This adds to several other features of the maxilla in which Carcharodontosauridae resemble Abelisauridae (Lamanna et al. 2002). The character state is similar in Mapusaurus and Giganotosaurus, except the small fenestra lies with a larger fossa (Coria & Currie 2006; Fig. 2J). Contra Coria & Currie (2006) and Brusatte & Sereno (2007), this fenestra is too small and its path is too oblique to the lateral surface of maxilla for it to be homologous to the maxillary fenestra of Allosaurus and Coelurosauria. Carrano et al. (2012) argued that the fenestra was homologous to the promaxillary fenestra of Allosaurus and Coelurosauria, but that too is unlikely because the fenestra in carcharodontosaurids lies more posteriorly, leaving no room for the maxillary fenestra between itself and the anterior edge of antorbital fenestra. Carrano et al. (2012) argued that a basal carcharodontosaurid Concavenator did possess a maxillary fenestra, making its absence in more derived members of Carcharodontosauridae a reversal. However, the character state appears similar to that of Mapusaurus and Giganotosaurus (small fenestra within a larger fossa), though damage to the maxilla makes this uncertain (Ortega et al.2010, fig. 3a). The single small fenestra in the antorbital fossa of the maxilla in Sinosaurus (Xing 2012; Fig. 2C) resembles those of both a basal neotheropod Dilophosaurus and a tetanuran Carcharodontosaurus. Piatnitzkysaurids Marshosaurus and Piatnitzkysaurus (Witmer 1997; Rauhut 2007; Fig. 2K, L), megalosaurids Afrovenator, Dubreuillosaurus (=”Poekilopleuron”; Allain (2005)), Eustreptospondylus, Megalosaurus, Sciurumimus (Witmer 1997; Allain 2002; Sadleir et al. 2008; Benson 2010; Rauhut et al. 2012; Fig. 2P, Q), Neovenator (Brusatte et al. 2008), and Monolophosaurus (Brusatte et al. 2010; Fig. 2R) share with Allosaurus and Coelurosauria a
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maxillary fenestra, but retain a medially enclosed maxillary antrum (medial wall is broken in the only known specimen of Neovenator). Megaraptoran Megaraptor also retains a medially enclosed maxillary antrum and one (probably the superior) of the two fenestrae in the antorbital fossa of its maxilla appears homologous to the maxillary fenestra (Porfiri et al. 2014; Fig. 2N). Promaxillary fenestra is clearly identifiable only in Marshosaurus and Neovenator (Witmer 1997; Brusatte et al. 2008; Fig. 2L), but, considering its obscurity in lateral view in Allosaurus and Albertosaurus (Fig. 2U, V), it may have been present in any of above basal tetanurans.
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Figure 2. Maxillae of Neotheropoda in lateral (top) and medial (bottom) views. (A) Coelophysis bauri, CM 31374, left, after Witmer (1997). (B) Dilophosaurus wetherilli, UCMP 77270, right (reversed), after Witmer (1997). (C) Sinosaurus triassicus, ZLJT01, right (reversed), after Xing (2012). (D) Ceratosaurus magnicornis, MWC 1, left, after Madsen & Welles (2000). (E) Masiakasaurus knopfleri, FMNH PR 2124, right (reversed), after Carrano et al. (2002). (F) Majungasaurus crenatissimus, FMNH PR 2100, left, after Sampson & Witmer (2007). (G) Suchomimus tenerensis, MNN GDF 501, right (reversed), after Carrano et al. (2012). (H) Irritator challengeri, SMNS 58022, left, photograph from www.science20.com. (I) Carcharodontosaurus saharicus, cast of SGM-Din 1, right (reversed), after Brusatte & Sereno (2007). (J) Giganotosaurus carolinii, MMCH-Pv 1, left, after Novas et al. (2013). (K) Piatnitzkysaurus floresi, PVL 4073, left, after Rauhut (2007). (L) Marshosaurus sp., CM 21704, right (reversed), photographed by the author. (M) Sinraptor dongi, IVPP 10600, left, after Currie & Zhao (1993). (N) Megaraptor namunhuaiquii, MUCPv 595, left, after Porfiri et al. (2014). (O) Torvosaurus gurneyi, ML 1100, left, after Hendrickx & Mateus (2014). (P)
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Dubreuillosaurus valesdunensis, MNHN 1998-13, right (reversed), after Allain (2002). (Q) Sciurumimus albersdoerferi, BMMS BK 11, left, under UV light, after Rauhut et al. (2012).
(R) Monolophosaurus jiangi, IVPP 84019, right (reversed), after Brusatte et al.
(2010). (S) Acrocanthosaurus atokensis, NCSM 14345, right (reversed), after Eddy & Clarke (2011). (T) Eocarcharia dinops, MNN GAD2, left, after Sereno & Brusatte (2008). (U) Allosaurus fragilis, USNM 8335, right (reversed), after Hendrickx & Mateus (2014). (V) Albertosaurus libratus, RTMP 83.35.100, left, after Witmer (1997). (W) Zuolong salleei, IVPP V15912, left, after Choiniere et al. (2010). Abbreviations: br, break (in the medial wall of maxillary antrum); fen, fenestra; fen ant, anterior fenestra; fen inf, inferior fenestra; fen max, maxillary fenestra; fen post, posterior fenestra; fen promax, promaxillary fenestra; fen sup, superior fenestra; fos, fossa; pila postantr, pila postantralis (postantral strut).
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Megalosaurid Torvosaurus shares both absence of a maxillary fenestra (Witmer 1997; Hendrickx & Mateus 2014; Fig. 2O) and a short (relative to the length of dorsal segment of vertebral column) pubis with spinosaurids Suchomimus (Fig. 3) and Spinosaurus (Ibrahim et al. 2014; fig. 2). In contrast, megalosaurids Afrovenator, Eustreptospondylus, and Megalosaurus (Sereno et al. 1994, fig. 2; Sadleir et al. 2008, fig. 1; Benson 2010; fig. 1; Fig. 3) share a longer pubis, resulting in a deeper trunk, also present in the majority of Ceratosauria and Tetanurae (Paul 1988). The trunk proportions of megalosaurid Sciurumimus are difficult to compare to those of other megalosaurids and spinosaurids because of the early ontogenetic stage of the only known specimen (Rauhut et al. 2012). Metriacanthosaurid Sinraptor shares with Allosaurus and Coelurosauria both the two fenestrae at the base of the ascending ramus of the maxilla and the medially open maxillary antrum. Witmer (1997) identified the more anterior of the two fenestrae as the promaxillary fenestra. However, this fenestra lies immediately anterior to a pila postantralis (Fig. 2M). Its position and large diameter suggest that the fenestra in question is homologous to the maxillary fenestra of Allosaurus and Coelurosauria. Yet, the pila postantralis in Sinraptor is much more robust than in Allosaurus and Coelurosauria, suggesting that the medial opening of the maxillary antrum in Metriacanthosauridae evolved independently from Allosauridae and Coelurosauria.
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Figure 3. Body shapes of Spinosauridae and Megalosauridae. (A) Suchomimus tenerensis, after Paul (2010). (B) Torvosaurus tanneri, after Paul (1988). (C) Eustreptospondylus oxoniensis, after Sadleir et al. (2008).
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Acrocanthosaurus and Eocarcharia share presence of three fenestrae in the antorbital fossa of the maxilla (Eddy & Clarke 2011; Fig. 2S, T). In both genera the larger anterior and posterior fenestrae are dorsoventrally elongated. Located superior to the posterior fenestra is a smaller accessory fenestra. This morphology of fenestrae in the antorbital fossa of the maxilla is unique in Tetanurae and supports Acrocanthosaurus and Eocarcharia forming a clade (Sereno & Brusatte 2008; Eddy & Clarke 2011) which is hereby named Acrocanthosauridae. Maxillary antrum is medially enclosed in Acrocanthosaurus, suggesting that its medial opening in Eocarcharia evolved independently from Sinraptor, Allosaurus, and Coelurosauria. Sereno & Brusatte (2008) and Eddy & Clarke (2011) identified posterior and anterior fenestrae in Eocarcharia and Acrocanthosaurus with maxillary and promaxillary fenestrae, respectively, in Allosaurus and Coelurosauria. However, this identification is questionable because the posterior fenestra lies posterior to a strut that may be homologous to the pila postantralis, in which case the anterior fenestra is homologous to the maxillary fenestra. If the latter identification is correct, the posterior fenestra in Acrocanthosaurus & Eocarcharia may be analogous to the postmaxillary fenestra lying posterior to the maxillary fenestra in tyrannosaurid Tarbosaurus (Hendrickx & Mateus 2014). Whichever identification of the anterior and posterior fenestrae in the antorbital fossa of the maxilla in Acrocanthosaurus and Eocarcharia is correct, the clade formed by these two genera must have evolved from an ancestor that possessed a maxillary fenestra.
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Morphology of quadratojugal In basal neotheropods Coelophysis and Dilophosaurus the dorsal ramus of quadratojugal is either a slender rod or tapers to a point (Fig. 4A, B), resulting in limited or absent contact with squamosal (Rowe 1989, fig. 1; Welles 1984, fig. 4). This character state is referred to as “slender two outer suspensorium bones” by Paul (1988). In Cryolophosaurus the dorsal ramus of quadratojugal is robust and even more so in basal neotheropod Zupaysaurus, in which it projects into lateral temporal fenestra (Fig. 4C, D). However, Sinosaurus (Fig. 4E) and ceratosaurians Ceratosaurus (Fig. 4F, G) and Abelisauridae (Majungasaurus (Fig. 4H), Carnotaurus (Bonaparte et al. 1990, fig. 2) and Skorpiovenator (Novas et al. 2013; fig. 6)) retain a slender or tapering dorsal ramus of quadratojugal, suggesting this character state is plesiomorphic for Tetanurae. A slender or tapering dorsal ramus of quadratojugal is retained in spinosaurid Suchomimus (Fig. 4I), carcharodontosaurids Concavenator and Tyrannotitan (Fig. 4J, K), metriacanthosaurids Sinraptor (Fig. 4L) and Yangchuanosaurus (Dong et al. 1983, fig. 45), and megalosaurid Dubreuillosaurus (Fig. 4M). Concavenator and Tyrannotitan also share a robust rostral ramus of quadratojugal, (tapers to a slender point in all other neotheropods, including the supposed carcharodontosaurid Acrocanthosaurus (Fig. 4O)) suggesting that this character state is a synapomorphy of Carcharodontosauridae. In contrast, Monolophosaurus, Acrocanthosaurus and Allosaurus (Fig. 4N, O, P) share with basal coelurosaurs Zuolong, Tanycolagreus, basal tyrannosauroid Proceratosaurus, and Ornitholestes (Paul 1988, p. 305) a robust dorsal ramus of quadratojugal, resulting in extensive contact with squamosal (Fig. 4Q, R, S).
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Figure 4. Quadratojugals of Neotheropoda in lateral view. (A) Coelophysis (=Syntarsus) kayentakatae, MNA V2623, left, after Rowe (1989). (B) Dilophosaurus wetherilli, UCMP 37302, left, after Welles (1984). (C) Cryolophosaurus ellioti, FMNH
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PR1821, right (reversed), after Smith et al. (2007). (D) Zupaysaurus rougieri, PULR 076, right (reversed), after Ezcurra & Novas (2007). (E) Sinosaurus triassicus, mounted cast at MSC, left, photographed by the author. (F) Ceratosaurus magnicornis, MWC 1, left, after Madsen & Welles (2000). (G) Ceratosaurus nasicornis, mounted cast at DDM, left, photographed by the author. (H) Majungasaurus crenatissimus, FMNH PR 2100, right (reversed), after Sampson & Witmer (2007). (I) Suchomimus tenerensis, MNN GDF 501, left, rostral ramus (stippled) restored, after Sereno et al. (1994). (J) Concavenator corcovatus, MCCM-LH 6666, right (reversed), in antero-lateral view, after Ortega et al. (2010). (K) Tyrannotitan chubutensis, MPEF-PV 1157, right (reversed), after Canale et al. (2013). (L) Sinraptor hepingensis, on display at ZDM, left, photograph from en.wikipedia.org/wiki/Sinraptor. (M) Dubreuillosaurus valesdunensis, MNHN 199813, right (reversed), after Allain (2002). (N) Monolophosaurus jiangi, IVPP 84019, right (reversed), after Brusatte et al. (2010). (O) Acrocanthosaurus atokensis, mounted cast of NCSM 14345 at Best Western Denver Southwest, right (reversed), photograph from www.youmustbetrippin.com. (P) Allosaurus sp., on display at DNM-QEH, right (reversed), photograph from www.nps.gov. (Q) Zuolong salleei, IVPP V15912, left, after Choiniere et al. (2010). (R) Tanycolagreus topwilsoni, TPII 2000-09-29, left, after Carpenter et al. (2005a). (S) Proceratosaurus bradleyi, NHM R 4860, right (reversed), after Rauhut et al. (2010). (T) Albertosaurus (=Gorgosaurus) libratus, cast of a CMI specimen, right (reversed), photograph from en/wikipedia.org/wiki/Gorgosaurus. (U) Garudimimus brevipes, GIN 100/13, right (reversed), after Kobayashi & Barsbold (2005). Abbreviations: br, break; df, post-mortem deformation (caudally bent dorsal ramus); dr, dorsal ramus; rr, rostral ramus.
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Contra Eddy & Clarke (2011), the preserved portion of the dorsal ramus of quadratojugal in Acrocanthosaurus is clearly more robust than in Sinraptor and Yangchuanosaurus. Tyrannosauridae, the most derived tyrannosauroids, converged with basal neotheropod Zupaysaurus in possessing a dorsal ramus of quadratojugal so robust that it projects into lateral temporal fenestra (Fig. 4T). This character state (“robust two outer suspensorium bones”) was noted in Proceratosaurus, Ornitholestes, Allosaurus, and Tyrannosauridae by Paul (1988). Morphology of quadratojugal is unclear in any of the published specimens of Compsognathidae, but it definitely reverted to the basal character state (tapering or slender dorsal ramus) in the most recent common ancestor of Maniraptoriformes, since it is present in both the basal (ornithomimosaur Garudimimus; Fig. 4U) and derived (dromaeosaurids Deinonychus and Velociraptor (Paul 1988)) members of the clade.
Morphology of posterior dentary In basal neotheropods Coelophysis and Zupaysaurus the posterior end of the dentary is notched by the external mandibular fenestra, the dorsal portion of the notch forming a narrow contact with the surangular (character 126, state 0 of Carrano et al. (2012); Fig. 5A, B). Contra Carrano et al. (2012), basal neotheropod Dilophosaurus possesses a derived state of this character in which the external mandibular fenestra is reduced and the surangular contact is expanded posteroventrally, resulting in a straight or slightly concave posterior end of dentary (character 126, state 1 of Carrano et al. (2012); Fig. 5C).
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Figure 5. Dentaries of Neotheropoda in lateral view. (A) Coelophysis (=Syntarsus) kayentakatae, MNA V2623, left, after Rowe (1989). (B) Zupaysaurus rougieri, PULR 076, right (reversed), after Ezcurra & Novas (2007). (C) Dilophosaurus wetherilli, UCMP 37303, left, after Welles (1984). (D) Sinosaurus triassicus, mounted cast at MSC, left, photographed by the author. (E) Ceratosaurus nasicornis, mounted cast at DDM, left, photographed by the author. (F) Majungasaurus crenatissimus, FMNH PR 2100, left, after Sampson & Witmer (2007). (G) Mapusaurus roseae, MCF-PVPH108.125, left, after Coria & Currie (2006). (H) Yangchuanosaurus shangyouensis, cast of CV 00215, left, photograph from www.sanherobot.com. (I) Australovenator wintonensis, AODF 604, left, after Hocknull et al. (2009). (J) Dubreuillosaurus valesdunensis, MNHN 1998-13, left, after Allain (2002). (K) Sciurumimus albersdoerferi, BMMS BK 11, left, under UV light, after Rauhut et al. (2012). (L) Monolophosaurus jiangi, IVPP 84019, right (reversed), after Brusatte et al. (2010). (M) Acrocanthosaurus atokensis, NCSM 14345, left, after Eddy & Clarke (2011). (N) Allosaurus fragilis, CM 11844, left, photographed by the author. (O) Proceratosaurus bradleyi, NHM R 4860, right (reversed), after Rauhut et al. (2010). (P) Albertosaurus (=Gorgosaurus) libratus, cast of a CMI specimen, right (reversed), photograph from www.ical.manchester.ac.uk. (Q) Garudimimus brevipes, GIN 100/13, right (reversed), after Kobayashi & Barsbold (2005). Abbreviations: sac, surangular contact.
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Sinosaurus (Fig. 5D) and ceratosaurians Ceratosaurus (Fig. 5E) and Abelisauroidea (Majungasaurus (Fig. F), Carnotaurus (Bonaparte et al. 1990, fig. 2), Skorpiovenator (Novas et al. 2013; fig. 6), and Masiakasaurus (Carrano et al. 2002, fig. 3)) retain a narrow surangular contact of dentary, suggesting this character state is plesiomorphic for Tetanurae. Although the dentary is known for a number of spinosaurids (Suchomimus, Baryonyx, Irritator, Spinosaurus), the posterior end is damaged in all known specimens, preventing evaluation of this character. The external mandibular fenestra does appear to be reduced in all of the above genera (Sereno et al. 1994, fig. 2; Charig & Milner 1997, fig. 13; Sues et al. 2002, fig. 1; Ibrahim et al. 2014; fig. S4). Although damaged, the best preserved dentary of carcharodontosaurid Mapusaurus suggests that a narrow surangular contact was retained in this genus (Fig. 5G). A narrow surangular contact was definitely retained in metriacanthosaurids Yangchuanosaurus (Fig. 5H) and Sinraptor (photograph of Sinraptor hepingensis on display at ZDM from en.wikipedia.org/wiki/Sinraptor) and in megaraptoran Australovenator (Fig. 5I). In contrast, megalosaurids Dubreuillosaurus and Sciurumimus (Fig. 5J, K), Monolophosaurus (Fig. 5L; contra Carrano et al. (2012)), Acrocanthosaurus and Allosaurus (Carrano et al. 2012; Fig. 5M, N) share with basal coelurosaurs Ornitholestes (Paul 1988, p. 305) and Tyrannosauroidea (both basal Proceratosaurus (Fig. 5O) and derived Tyrannosauridae represented by Albertosaurus (Fig. 5P)) a posteroventrally expanded surangular contact. This character state is retained in compsognathids Juravenator and Compsognathus (Chiappe & Göhlich 2010, fig. 10) and in both basal (ornithomimosaur Garudimimus (Fig. 5Q)) and derived (dromaeosaurids Dromaeosaurus and Velociraptor and troodontid Troodon (Paul 1988, pp. 362, 363, 398)) members of Maniraptoriformes. Its retention in small-skulled (relative to body size) and
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toothless Garudimimus despite the presence of large (≈50% dorsoventral mandibular depth) external mandibular fenestra is particularly notable.
Morphology of femoral lesser trochanter Unlike the other characters in this phylogenetic analysis (and the vast majority of characters in other phylogenetic analyses), character state changes in the morphology of the lesser trochanter of the femur have a probable functional basis. Carrano (2000) found that the femoral lesser trochanter increased in size and proximal extent independently in several different dinosaur clades, including Theropoda. He argued that this was an adaptation to increase the leverage of M. iliofemoralis, a powerful protractor of the femur which inserts on this process. Such interpretation of the functional significance of this character state change is supported by the observation that increase in the proximal extent (“elevation”) of the lesser femoral trochanter occurred simultaneously with or shortly after the expansion of preacetabular ilium, the origin of M. iliofemoralis. Given the selective advantage of improved leverage of femoral protractor in a terrestrial vertebrate with upright hind limbs, it is not surprising that Carrano (2000) found no examples of reversal in the morphology of femoral lesser trochanter (reduction in size and proximal extent) in Dinosauria. In basal neotheropods Coelophysis and Dilophosaurus and in Cryolophosaurus the lesser trochanter is both small and extends proximally to or slightly past the ventral margin of the femoral head (Carrano et al. 2012; Fig. 6A, B, C). In ceratosaurians Ceratosaurus (Fig. 6E) and Abelisauroidea (Carnotaurus (Fig. 6F), Eoabelisaurus (Paul & Rauhut 2012, fig.3), and Masiakasaurus (Carrano et al. 2002, fig. 14)) the lesser trochanter is enlarged, but its proximal extent remains the same, suggesting that this character state is plesiomorphic for Tetanurae.
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Figure 6. Femora of Neotheropoda in anterior view. Horizontal line marks the proximal extent of the lesser trochanter. (A) Coelophysis (=Syntarsus) kayentakatae, MNA V2623, right, after Rowe (1989). (B) Dilophosaurus wetherilli, UCMP 37302, left (reversed), after Welles (1984). (C) Cryolophosaurus ellioti, FMNH PR1821, right, after Smith et al. (2007). (D) Sinosaurus triassicus, mounted cast at MSC, left (reversed), photographed by the author. (E) Ceratosaurus dentisulcatus, UUVP 56, left (reversed), after Madsen & Welles (2000). (F) Carnotaurus sastrei, MACN-CH 894, right, after Bonaparte et al. (1990). (G) Suchomimus tenerensis, mounted cast at FPDM, left (reversed), photograph from www.kansai.gr.jp; ac, acetabular rim obstructing medial edge of the femoral head. (H) Irritator challengeri, mounted skeleton at MU-UFRJ, left (reversed), photograph from www.flickr.com/people/36197880@N03 Kabacchi. (I) Mapusaurus roseae, MCF-PVPH-108.203, left (reversed), after Coria & Currie (2006). (J) Tyrannotitan chubutensis, MPEF-PV 1157, right, after Canale et al. (2013). (K) Piatnitzkysaurus floresi, PVL 4073, right, after Molnar et al. (1990). (L) Australovenator wintonensis, AODF 604, right, after Hocknull et al. (2009). (M) Sinraptor dongi, IVPP 10600, right, after Currie & Zhao (1993). (N) Eustreptospondylus oxoniensis, OUMNH
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J. 13558, left (reversed), after Sadleir et al. (2008). (O) Neovenator salerii, MIWG 6348, right, after Brusatte et al. (2008). (P) Acrocanthosaurus atokensis, SMU 74646 2B–1 J, right, after D’Emic et al. (2012). (Q) Allosaurus fragilis, left (reversed), after Madsen (1976). (R) Tanycolagreus topwilsoni, TPII 2000-09-29, right, after Carpenter et al. (2005a). (S) Guanlong wucaii, IVPP V14531, right, photograph from www.brazband.com. (T) Tyrannosaurus rex, FMNH PR2081, right, after Brochu (2003). (U) Gallimimus bullatus, ZPAL Mg.D-I/94, left (reversed), after Osmolska et al. (1972). (V) Garudimimus brevipes, GIN 100/13, right, after Kobayashi & Barsbold (2005). (W) Beishanlong grandis, FRDC-GS GJ (06) 01–18, right, after Makovicky et al. (2010).
Contra Carrano et al. (2012), a large lesser trochanter extending proximally to or slightly past the ventral margin of the femoral head (character 305, state 0) is retained in Sinosaurus (Fig. 6D), in spinosaurids Suchomimus, Irritator (Fig. 6G, H), and Spinosaurus (Ibrahim et al. 2014, fig. 2) and in carcharodontosaurids Mapusaurus, Tyrannotitan (Fig. 6I, J), Giganotosaurus (Currie & Carpenter 2000), and Concavenator (Ortega et al. 2010, fig. 1). Largely in agreement with Carrano et al. (2012), the lesser trochanter extends proximally to the middle of femoral head (character 305, state 1) in piatnitzkysaurid Piatnitzkysaurus (Fig. 6K), metriacanthosaurids Sinraptor (Fig. 6M) and Yangchuanosaurus (Dong et al. 1983, fig. 53), megalosaurids Eustreptospondylus (Fig. 6N) and Afrovenator (Sereno et al. 1994, fig. 2), Neovenator (Fig. 6O), Acrocanthosaurus (Fig. 6P), and Allosaurus (Fig. 6Q). This character state is retained by basal coelurosaurs Coelurus (Carpenter et al. 2005b, fig. 3.11), Tanycolagreus (Fig. 6R), basal tyrannosauroid Guanlong (Fig. 6S), and ornithomimosaurs Gallimimus and Garudimimus (Fig. 6U, V).
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Morphology of the lesser trochanter is unclear in any of the published specimens of Compsognathidae. In megaraptorans and derived tyrannosauroids of the family Tyrannosauridae (Novas et al. 2013; Fig. 6L, T) and in ornithomimosaur Beishanlong (Fig. 6W) the lesser trochanter extends proximally to the dorsal margin of femoral head (character 305, state 2 of Carrano et al. (2012)).
Morphology of distal scapula Coelophysis, Dilophosaurus and Sinosaurus share an expanded distal end of the scapula (character 222, state 0 of Carrano et al. (2012); Fig. 7A, B, C). In contrast, ceratosaurians Ceratosaurus and Carnotaurus (Fig. 7D, E) share with Tetanurae a scapula with a distal end that is either no wider than the more proximal portion of the blade (Fig. 7F, G, H) or tapers gradually in the proximal direction (Fig. 7I, J) (character 222, state 1 of Carrano et al. (2012)).
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Figure 7. Scapulae/scapulocoracoids of non-coelurosaurian Neotheropoda in medial (A) and lateral (B-J) views. (A) Coelophysis (=Syntarsus) kayentakatae, MNA V2623, right, after Rowe (1989). (B) Dilophosaurus wetherilli, UCMP 37302, left (reversed), after Welles (1984). (C) Sinosaurus triassicus, mounted cast at MSC, right, photographed by the author. (D) Ceratosaurus dentisulcatus, UUVP 317, right, after Madsen & Welles (2000). (E) Carnotaurus sastrei, MACN-CH 894, left (reversed), after Bonaparte et al. (1990). (F) Giganotosaurus carolinii, mounted cast of MUCPv-Ch1 at MSC, left (reversed), photographed by the author. (G) Concavenator corcovatus, MCCM-LH 6666, right, after Ortega et al., (2010). (H) Megalosaurus bucklandii, OUMNH J. 13574, right, after Benson (2010). (I) Sciurumimus albersdoerferi, BMMS
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BK 11, left (reversed), under UV light, after Rauhut et al. (2012). (J) Allosaurus fragilis, cast, right, after Madsen (1976). Abbreviations: co, coracoid.
Length/presence of metacarpal IV This character can be evaluated only in those few taxa for which a complete or nearly complete manus is known. In basal neotheropods Coelophysis (=Syntarsus) (Rowe & Gauthier 1990, fig. 5.6) and Dilophosaurus (Welles 1984, fig. 29) and in ceratosaurians Ceratosaurus and Eoabelisaurus (Fig. 8A, B) metacarpal IV is > 50% length of metacarpal III and, with the exception of Eoabelisaurus, has at least one phalanx attached to it, suggesting that this character state is plesiomorphic for Tetanurae. In metriacanthosaurid Sinraptor and megaraptoran Megaraptor metacarpal IV is < 50% but > 25% length of metacarpal III (Fig. 8C, D). Metacarpal IV is absent in megalosaurid Sciurumimus (Rauhut et al. 2012), Acrocanthosaurus (Currie & Carpenter 2000), Allosaurus (Madsen 1976), and in all coelurosaurs (for which a complete manus is known) other than basal tyrannosauroid Guanlong (Rauhut et al. 2012). In the latter metacarpal IV is < 25% length of metacarpal IV (Fig. 8E). In all tetanurans, in which it is present, metacarpal IV does not have a phalanx attached to it. The above data suggest that either metacarpal IV was lost independently in non-coelurosaurian tetanurans and Coelurosauria or its presence in Guanlong is a reversal. In either case, the common ancestor of Megalosauridae, Acrocanthosauridae, Allosauridae and Coelurosauria must have possessed a more reduced metacarpal IV than Metriacanthosauridae and Megaraptora.
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Figure 8. Metacarpals III and IV of Neotheropoda. (A) Ceratosaurus nasicornis, USNM 4735, left, in dorsal view, after Rowe & Gauthier (1990). (B) Eoabelisaurus mefi, MPEF PV 3990, right, in plantar view, after Pol & Rauhut (2012). (C) Sinraptor dongi, IVPP 10600, left, in dorsal view, after Currie & Zhao (1993). (D) Megaraptor namunhuaiquii, MCF-PVPH 79, right, in lateral view (reversed) after Calvo et al. (2004). (E) Guanlong wucaii, IVPP V14531, left, in plantar view, after Xu et al. (2006).
Rib cage shape This character can be evaluated only in those few taxa for which a complete and undistorted rib cage is known. Metriacanthosaurid Yangchuanosaurus shares with ceratosaurians Ceratosaurus (Paul 1988) and Carnotaurus a rib cage that is mediolaterally narrow relative to its anteroposterior length (Fig. 9A, B, C). In contrast, similar-sized Allosaurus shares with coelurosaurs Albertosaurus and other tyrannosaurids (Paul 1988) a wider rib cage (Fig. 9D, E).
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Figure 9. Skeletal reconstructions of Neotheropoda in dorsal view illustrating rib cage shape. (A) Ceratosaurus nasicornis. (B) Carnotaurus sastrei. (C) Yangchuanosaurus shangyouensis. (D) Allosaurus fragilis. (E) Albertosaurus libratus. After Paul (2010).
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DISCUSSION Revised phylogeny of non-coelurosaurian Tetanurae A small lesser trochanter extending proximally to below the ventral margin of femoral head indicates that Cryolophosaurus is a neotheropod more basal than Ceratosauria (Fig. 10). A robust dorsal ramus of quadratojugal does not contradict this phylogenetic position, because a similarly basal neotheropod Zupaysaurus has evolved an even more robust dorsal ramus (projecting into lateral temporal fenestra) independently from Tyrannosauridae and other basal coelurosaurs. A large lesser trochanter extending slightly past the ventral margin of the femoral head indicates that Sinosaurus is more derived than Coelophysis, Dilophosaurus, and Cryolophosaurus. However, Sinosaurus does retain an expanded distal end of the scapula found in Coelophysis and Dilophosaurus, which suggests that it is less derived than Ceratosauria. Absence of a maxillary fenestra and a lesser trochanter extending proximally or slightly past the ventral margin of the femoral head suggest that Spinosauridae and Carcharodontosauridae (excluding Acrocanthosauridae) are the most basal tetanurans (Fig. 10). Piatnitzkysauridae, Neovenator, Megaraptora, Metriacanthosauridae, Megalosauridae, Monolophosaurus, Acrocanthosauridae and Allosauridae share with Coelurosauria a maxillary fenestra and, with the exception of Megaraptora and Monolophosaurus, a lesser trochanter extending proximally to the middle of femoral head, suggesting that all these tetanurans form a clade. Morphology of the lesser trochanter (and the rest of the femur) is unknown in Monolophosaurus, while Megaraptora appear to have converged with coelurosaurs Tyrannosauridae and ornithomimosaur Beishanlong in possessing a lesser trochanter extending proximally to the dorsal margin of femoral head.
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Figure 10. Phylogeny of Neotheropoda with revised phylogeny of non-coelurosaurian Tetanurae. Apomorphies: 1, large lesser trochanter; 2, distal end of scapula not expanded; 3, lesser trochanter extending proximally to the middle of femoral head; 4, maxillary fenestra present; 5, posteroventrally expanded surangular contact of dentary; 6, robust dorsal ramus of quadratojugal; 7, maxillary antrum medially open; 8, lesser trochanter extending proximally to the dorsal margin of femoral head; 9, metacarpal IV < 25% length of metacarpal III or absent; 10, robust rostral ramus of quadratojugal.
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Megalosauridae, Monolophosaurus, Acrocanthosauridae and Allosauridae share with Coelurosauria a posteroventrally expanded surangular contact of dentary, suggesting that they form a clade which is hereby referred to as Avetheropoda following Paul (1988, 2010), who listed this character state of the posterior dentary (“double-hinged lower jaws”, “extra joint in lower jaw better developed”) among the defining synapomorphies of the clade. Oddly, Paul (2010) included metriacanthosaurids Sinraptor and Yangchuanosaurus among and excluded Megalosauridae from Avetheropoda, despite the former retaining the narrow surangular contact and the latter possessing the posteroventrally expanded one. Another defining synapomorphy of Avetheropoda may be a metacarpal IV that is < 25% length of metacarpal III or absent, though data on this character is limited. Retention of a metacarpal IV > 25% length of metacarpal III in Metriacanthosauridae and Megaraptora supports the position of these two tetanuran clades outside of Avetheropoda. The absence of maxillary fenestra (morphology of the lesser trochanter and posterior dentary are unknown) and shallow trunk of Torvosaurus suggest that it forms a clade with Spinosauridae and falls outside of Megalosauridae and Avetheropoda. However, all previous phylogenetic analyses have placed Torvosaurus as a sister genus to Megalosaurus (Benson 2010; Carrano et al. 2012) and the similarity between the two genera has led Paul (1988) to propose their synonymization. Therefore, until future discoveries clarify the morphology of posterior dentary and femoral lesser trochanter in Torvosaurus, its absence of maxillary fenestra is most parsimoniously regarded as a reversal and its shallow trunk – as having evolved independently from that of Spinosauridae.
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Monolophosaurus, Acrocanthosauridae (containing Acrocanthosaurus & Eocarcharia) and Allosauridae (containing Allosaurus & Saurophaganax) share with basal Coelurosauria a robust dorsal ramus of quadratojugal, suggesting that they form a clade which is hereby named Euavetheropoda. Allosauridae also share with Coelurosauria a medially open maxillary antrum, suggesting that they form a clade. This character state evolved independently in Sinraptor (Metriacanthosauridae) and Eocarcharia (Acrocanthosauridae). Further support for a more derived position within Tetanurae of Allosauridae relative to Metriacanthosauridae is provided by a wide rib cage shared by Allosaurus and Tyrannosauridae, though data on this character is limited The phylogenetic positions of Piatnitzkysauridae and Neovenator are highly uncertain because morphology of posterior dentary and quadratojugal is unknown in both taxa. Both are more derived than Spinosauridae and Carcharodontosauridae and less derived than Allosauridae, but either Piatnitzkysauridae or Neovenator or both may lie outside of Avetheropoda (Fig. 10) or be avetheropods outside or among Euavetheropoda. Neovenator may be a sister group to Megaraptora, as argued by Benson et al. (2010). Alternatively, Neovenator may be a sister group of Acrocanthosauridae, especially since it shares a medially elevated femoral head with Acrocanthosaurus among those tetanurans in which the lesser trochanter extends proximally to the middle of femoral head (character 302, state 2 of Carrano et al. (2012); Fig. 6O, P). This would be in partial agreement with conclusions of Sereno & Brusatte (2008) and Eddy & Clarke (2011), who found Neovenator to be a sister group of Carcharodontosauridae including the Acrocanthosaurus and Eocarcharia clade (named Acrocanthosauridae in this presentation). Some of the conclusions reached in this presentation are in agreement with those of at least some previous publications. These include placement of Cryolophosaurus and Sinosaurus
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as neotheropods more basal than Ceratosauria, placement of Spinosauridae as the most basal tetanuran clade and placement of Monolophosaurus, Acrocanthosaurus and Eocarcharia, and Allosauridae as more derived tetanurans forming a clade with Coelurosauria. The biggest differences between the phylogeny of non-coelurosaurian Tetanurae supported by this presentation and the one supported by a majority of previous publications (Figs. 1, 10) are placement of Carcharodontosauridae, other than Acrocanthosaurus and Eocarcharia, among the most basal tetanurans and placement of Megalosauridae as more derived than either Carcharodontosauridae or Metriacanthosauridae, rendering both Megalosauroidea and Allosauroidea polyphyletic.
Homoplasies in phylogeny of non-coelurosaurian Tetanurae supported by previous publications This drastic revision of basal tetanuran phylogeny is overwhelmingly supported by the 10 characters examined in this presentation. In contrast, the phylogeny of Carrano et al. (2012), which is representative of the current consensus, involves the following 19 homoplasies in these characters. It requires Cryolophosaurus to reduce the size of lesser trochanter, Sinosaurus to expand distal end of scapula, Monolophosaurus to evolve robust dorsal ramus of quadratojugal and posteroventrally expanded surangular contact of dentary independently of Avetheropoda, Spinosauridae and Carcharodontosauridae to independently lose maxillary fenestra and reduce proximal extent of lesser trochanter, Megalosauridae to posteroventrally expand surangular contact of dentary and lose metacarpal IV independently of Avetheropoda, Acrocanthosaurus and Allosaurus to evolve robust dorsal ramus of quadratojugal and posteroventrally expanded surangular contact of dentary independently of each other and to lose metacarpal IV
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independently of Coelurosauria, Acrocanthosaurus to revert to tapering rostral ramus of quadratojugal (from robust one of other carcharodontosaurids), and Allosaurus to evolve a medially open maxillary antrum and wide rib cage independently of Coelurosauria. As discussed in the Results, reduction in size and proximal extent of lesser trochanter is unlikely on functional grounds and has not occurred in Dinosauria outside of Theropoda. Nor does it seem likely that gigantic (1.7-4.4 tonnes), tall-skulled (length/height > 3.0) Allosaurus and Acrocanthosaurus converged with small (13-50 kg), low-skulled (length/height < 3.0) Zuolong, Proceratosaurus, and Ornitholestes in skull characters (robust dorsal ramus of quadratojugal and posteroventrally expanded surangular contact of dentary). (Skull reconstructions and body mass estimates from Choiniere et al. (2010) and Paul (2010).) Carrano et al. (2012) acknowledged several derived character states shared by Allosaurus and Coelurosauria, but argued that these were homoplasies because of strong support (11 synapomorphies) for Allosauroidea provided by their analysis. Carrano et al. (2012) also found strong support for Megalosauroidea (8 synapomorphies). However, the pruning of a few genera known from fragmentary remains from their analysis reduced support for Allosauroidea and Megalosauroidea to 3 and 2 synapomorphies, respectively (Carrano et al. 2012).
Multiple homoplasies in Neotheropoda The basal tetanuran phylogeny proposed in this presentation does involve numerous homoplasies. However, so do the phylogenies supported by previous publications, including that of Carrano et al. (2012). This includes obturator foramina of pubis and ischium open into notches (character 281, state 2) listed as a synapomorphy of Avetheropoda. Both foramina are enclosed by bone in metriacanthosaurid Yangchuanosaurus (Dong et al. 1983, fig. 52) but both
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are open into notches in metriacanthosaurid Sinraptor (Zhao & Currie 1993, fig. 21). Similarly, both pubic and ischiadic obturator foramina are enclosed in basal tyrannosauroid Guanlong (Xu et al. 2006, fig. 2), but open in more derived tyrannosauroids of the family Tyrannosauridae (Molnar et al. 1990, fig. 6.9). This indicates that opening of these foramina occurred repeatedly within Avetheropoda, whether or not it includes Metriacanthosauridae. Slender scapula (character 223, state 2 of Carrano et al. (2012)) evolved independently (or reverted to robust state) in Megalosauridae and Carcharodontosauridae since both families include members with robust and slender scapulae (Fig. 7F-I), whether or not Carcharodontosauridae includes Acrocanthosaurus & Eocarcharia or is a sister clade to Allosauridae. Similarly, anteriorly expanded distal end of pubis (character 288, state 1 of Carrano et al. (2012)) evolved in Carcharodontosauridae (or common ancestor of Carcharodontosauridae and Allosauridae) independently of Coelurosauria, whether carcharodontosaurids are outside or among Avetheropoda. This character state also evolved independently in Abelisauridae among ceratosaurians (Bonaparte et al. 1990, fig. 31; Sereno & Brusatte 2008, fig. 7). The most striking example of multiple homoplasies in Neotheropoda is independent evolution of an enlarged antorbital fenestra resulting in a reduced anterior ramus of maxilla and a postorbital that contacts the lacrimal and projects into the orbit in ceratosaurians Abelisauridae (Sampson & Witmer 2007), basal tetanurans Carcharodontosauridae (Eddy & Clarke 2011), and coelurosaur Lythronax (Leowen et al. 2013), suggesting that the above character states form a functionally linked suite. If that is the case, independent evolution of these 3 character states in Acrocanthosauridae, suggested in this presentation, only increases the number homoplasies for this character suite from 3 to 4. Notably, Acrocanthosaurus lacks the rugose nasals present in Abelisauridae (Sampson & Witmer 2007), Carcharodontosauridae (Eddy & Clarke 2011), and
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Lythronax & other tyrannosaurids (Leowen et al. 2013), providing an additional argument for Acrocanthosauridae being a clade outside of Carcharodontosauridae. Placement of Megaraptora outside of Coelurosauria (Benson et al. 2010; Carrano et al. 2012; this presentation) contra Novas et al. (2013) and Porfiri et al. (2014) involves independent evolution of several distinctive character states in Megaraptora and Tyrannosauroidea (among which the latter two publications place Megaraptora). However, some of these character states must have evolved more than once in Coelurosauria. These include D-shaped premaxillary teeth, one of the most distinctive synapomorphies of Tyrannosauroidea, which evolved independently in basal coelurosaurs Zuolong and Ornitholestes while being absent in Tanycolagreus (Porfiri et al. 2014). Moreover, D-shaped premaxillary teeth had evolved independently in abelisaurid Indosuchus (Chatterjee 1978; Bonaparte et al. 1990). Similarly, a lesser trochanter extending proximally to the dorsal margin of femoral head evolved independently in derived tyrannosauroids (including Tyrannosauridae) and ornithomimosaur Beishanlong (Deinocheiridae) since basal tyrannosauroid Guanlong and ornithomimosaurs Garudimimus (Deinocheiridae) and Gallimimus (Ornithomimidae) retain a lesser trochanter extending proximally to the middle of the femoral head. Existence of functionally linked suites of character states may explain the existence of numerous synapomorphies supporting Megalosauroidea and Allosauroidea despite evidence against monophyly of these two clades presented here. As noted by Carrano et al. (2012), Megalosauroidea possess a low skull (length/height > 3.0), while Allosauroidea – a tall skull (length/height < 3.0). Carrano et al. (2012) argued that the latter condition was plesiomorphic for Tetanurae. However, a low skull is present in basal neotheropods Dilophosaurus and Coelophysis (Welles 1984, fig. 4; Rowe 1989, fig. 1), ceratosaurians Noasauridae (Carrano et al.
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2002, figs. 2, 22), and basal Coelurosauria, with the exception of Tyrannosaurinae (skull reconstructions from Paul (2010) and Leowen et al. (2013, figs. 2, 3)), suggesting that this character state is plesiomorphic for Tetanurae. Therefore, some of the 8 cranial synapomorphies supporting Megalosauroidea (Carrano et al. 2012) may be part of a plesiomorphic character suite associated with a low skull shape. The basal position of Monolophosaurus among Tetanurae supported by Carrano et al. (2012) may also be due to its retention of a low skull shape (Brusatte et al. 2010, fig. 1). On the other hand, some of the 6 cranial synapomorphies (out of a total of 11) supporting Allosauroidea (Carrano et al. 2012) may be part of an apomorphic character suite associated with a tall skull shape, which has evolved independently in Zupaysaurus (Ezcurra & Novas 2007), Ceratosauria (Carrano et al. 2012), Tyrannosaurinae, and, according to this presentation, in Carcharodontosauridae, Metriacanthosauridae, and the common ancestor of Acrocanthosauridae and Allosauridae. Notably, posteroventrally expanded surangular contact of dentary and robust dorsal ramus of quadratojugal, 2 synapomorphies supporting Avetheropoda and Euavetheropoda, respectively, in this presentation, are not part of a character suite since the former evolved in the low-skulled Dilophosaurus and the latter – in the tall-skulled Zupaysaurus independently of Tetanurae (Fig. 10). The above speculation and revised phylogeny of non-coelurosaurian Tetanurae can only be tested by a new quantitative phylogenetic analysis of Neotheropoda examining or reexamining a large number of characters in addition to the few re-examined in this presentation. Demonstrating the need for such an analysis to clarify the phylogenetic relationships between basal tetanurans (as opposed to having his present conclusions accepted) and carrying out such an analysis in collaboration with a more experienced colleague are the main motivations of the author of this presentation.
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CONCLUSIONS 1. Cryolophosaurus possesses a small lesser trochanter, indicating it is among the most basal neotheropods (Coelophysis, Dilophosaurus). 2. Sinosaurus retains a distally expanded scapula of the most basal neotheropods but shares with Ceratosauria and Tetanurae a large lesser trochanter, suggesting that it is more derived than the former but less derived than the latter. 3. Spinosauridae and Carcharodontosauridae (except Acrocanthosaurus and Eocarcharia) possess a lesser trochanter extending proximally to the ventral margin of femoral head and lack a maxillary fenestra, suggesting that they are the most basal tetanurans. 4. Piatnitzkysauridae, Neovenator, Megaraptora, Metriacanthosauridae, Megalosauridae, Acrocanthosauridae (Acrocanthosaurus, Eocarcharia) and Allosauridae (Allosaurus, Saurophaganax) share with basal Coelurosauria (Zuolong, Tanycolagreus, Coelurus, Tyrannosauroidea) a lesser trochanter extending proximally to the middle of femoral head (lesser trochanter extends proximally to the dorsal margin of femoral head in Megaraptora, Tyrannosauridae, and ornithomimosaur Beishanlong). The above basal tetanurans and Monolophosaurus also share with Coelurosauria a maxillary fenestra. 5. Megalosauridae, Monolophosaurus, Acrocanthosauridae and Allosauridae share with Coelurosauria a posteroventrally expanded surangular contact of dentary and a metacarpal IV less than 25% of metacarpal III or absent, forming a clade Avetheropoda.
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6. Monolophosaurus, Acrocanthosauridae, and Allosauridae share with basal Coelurosauria (Zuolong, Tanycolagreus, Tyrannosauroidea, Ornitholestes) a robust dorsal ramus of quadratojugal, forming a clade Euavetheropoda. 7. Allosauridae share with Coelurosauria a medially open maxillary antrum (evolved independently in Metriacanthosauridae and Eocarcharia). 8. Cranial synapomorphies supporting basal tetanuran clades Megalosauroidea and Allosauroidea in previous publications may be part of functionally linked character suites associated with a plesiomorphically low skull in the former and an apomorphically tall skull in the latter, making it more likely that these character states evolved multiple times as suggested by this presentation.
ACKNOWLEDGEMENTS I thank Mr. Nick Wiersum, curator of Dinosaur Discovery Museum (Kenosha, WI), for his kind assistance in photographing the mounted casts of theropod skeletons at the museum. This presentation is supported by the Biology Department of George Mason University (chaired by Dr. Larry Rockwood).
Title art “Megalosauroidea” from www.snipview.com “Allosauroidea Skulls” from iguana-teteia at deviantart.com
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