A reappraisal of a putative record of abelisauroid theropod dinosaur from the Middle Jurassic of England

Proceedings of the Geologists’ Association 123 (2012) 779–786

Contents lists available at SciVerse ScienceDirect

Proceedings of the Geologists’ Association journal homepage: www.elsevier.com/locate/pgeola

A reappraisal of a putative record of abelisauroid theropod dinosaur from the Middle Jurassic of England Oliver W.M. Rauhut * Bayerische Staatssammlung fu¨r Pala¨ontologie und Geologie and Department of Earth and Environmental Sciences, Ludwig-Maximilians-University, Richard-Wagner-Str. 10, 80333 Munich, Germany

A R T I C L E I N F O

A B S T R A C T

Article history: Received 2 February 2012 Received in revised form 21 May 2012 Accepted 26 May 2012 Available online 7 July 2012

Abelisauroidea are a recently recognized clade of theropod dinosaurs that have a predominantly Gondwanan distribution. Recently, a distal theropod tibia from the Middle Jurassic of England was identified as an abelisauroid, representing one of the oldest records of the group in general and the only Jurassic occurrence in Europe. On this basis, rapid radiation of abelisauroid and a global distribution of this clade in the Jurassic were suggested. Here, the specimen in question is re-examined and the characters used for referral to the Abelisauroidea are re-evaluated. None of the proposed characters can be demonstrated to represent abelisauroid synapomorphies and all have a wider distribution; especially coelurosaurian theropods, which are known from contemporaneous beds in England, frequently show the same character combination. Thus, there is currently no secure evidence for the occurrence of abelisauroids in the Jurassic of the northern Hemisphere, and the early evolution of this clade remains poorly known. Furthermore, other fragmentarily known taxa previously referred to Abelisauroidea based on putative synapomorphies of the distal tibia, such as Ozraptor and Austrocheirus, should be considered as Theropoda indet. ß 2012 The Geologists’ Association. Published by Elsevier Ltd. All rights reserved.

Keywords: Abelisauroidea Theropods Middle Jurassic Palaeobiogeography

1. Introduction Abelisauroidea are one of the more recently recognized major clades of theropod dinosaurs (Bonaparte and Novas, 1985; Bonaparte, 1991a). They are phylogenetically basal, but include some of the morphologically most derived theropod dinosaurs known. Currently, some twenty to twenty five formally named, valid taxa are referred to this clade (Carrano and Sampson, 2008; Novas, 2009; Ezcurra et al., 2010), all but one of them of late Early to Late Cretaceous age, and all but one (Genusaurus from the Albian of France) were found in Gondwana. Although the occurrence of their sister taxon, the Ceratosauridae, in the Late Jurassic of North America, Europe, Africa, and South America (Madsen and Welles, 2000; Mateus et al., 2006; Soto and Perea, 2008; Rauhut, 2011) indicates that the clade must reach back to at least the Late Jurassic as well, only one Jurassic abelisauroid has been securely identified (a new taxon from the Middle Jurassic of Patagonia; Pol and Rauhut, in press), and other Jurassic abelisauroid occurrences so far are sparse and based on fragmentary and often questionable remains (Maganuco et al., 2005, 2007; Rauhut, 2005, 2011; Allain

* Tel.: +49 89 2180 6645; fax: +49 89 2180 6601. E-mail address: [email protected].

et al., 2007; Carrano and Sampson, 2008). Thus, the origin and early evolutionary and biogeographic history of abelisauroids is still poorly understood. Recently, Ezcurra and Agnolin (2012) reinterpreted a theropod specimen from the Bathonian Stonesfield Slate of England as the oldest abelisauroid record from the northern hemisphere, which would have important implications for our understanding of early abelisauroid evolution and biogeography. The specimen consists of the poorly preserved distal end of a left tibia, for which Ezcurra and Agnolin (2012) proposed four derived characters that led to their identification of the specimen as abelisauroid. Given the potential importance of this interpretation, these characters are here reevaluated, following a detailed re-examination of the specimen and in the context of a broader taxon sample of theropod dinosaurs. Institutional abbreviations. CCG, Chengdu College of Geology, Chengdu, China; JME, Jura Museum Eichsta¨tt, Germany; MB, Museum fu¨r Naturkunde, Berlin, Germany; MCNA, Museo de Ciencias Naturales y Antropolo´gicas ‘‘Cornelio Moyano’’, Mendoza, Argentina; MNN, Muse´e National du Niger, Niamey, Niger; OUMNH, Oxford University Museum of Natural History, Oxford, Great Britain; UA, Universite´ d’Antananarivo, Madagascar; UCMP, University of California, Museum of Paleontology, Berkeley, USA; UMNH, Utah Museum of Natural History, Salt Lake City, USA; YPM, Yale Peabody Museum, New Haven, USA.

0016-7878/$ – see front matter ß 2012 The Geologists’ Association. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.pgeola.2012.05.008

780

O.W.M. Rauhut / Proceedings of the Geologists’ Association 123 (2012) 779–786

2. Materials and methods The specimen in question (MB R. 2351; Fig. 1) was excavated from the Stonesfield Slate of Oxfordshire, England. The exact time or place of discovery are unknown, but the slate was mined in the vicinity of Stonesfield, some 15 km northwest of Oxford, up to 1911 (Benson, 2009). The Stonesfield Slate is part of the Taunton Limestone Formation, which is early Bathonian in age. It has yielded a rather large number of mainly isolated theropod remains, which were washed into the shallow marine environment, presumably during storm events (Benson, 2009). The vast majority of theropod remains from the Stonesfield Slate can be referred to the large megalosauroid theropod Megalosaurus, but remains of one or two smaller taxa are also present (Benson, 2009, 2010). The specimen MB R. 2351 is the distal end of a left tibia of a small theropod dinosaur. Only about 20–25% of the total length of the bone is preserved. The proximal break shows sharp edges, indicative of damage during collection or preparation, as is often the case in theropod specimens from Stonesfield (Benson, 2009). Although most theropod bones from the Stonesfield Slate show few signs of abrasion, this small tibia has both malleoli abraded to the spongiosa, and the distal articular surface also exhibits signs of wear. The specimen was first described by Galton and Molnar

(2005), who referred it to an unspecified basal tetanuran. A detailed redescription is therefore not necessary, and this work will mainly concentrate on the discussion of potentially phylogenetically informative characters exhibited by this poorly preserved bone and their distribution within theropod dinosaurs. Comparisons with other theropod tibiae were carried out on the basis of own observations, detailed photographs provided by colleagues, and the literature. Especially in the case of coelurosaurs, but also in several basal theropods and ceratosaurs, comparisons were hampered by the fact that tibiae are often preserved in articulation with the proximal tarsals, not allowing any direct observation of the anterior side of the distal end or the distal outline of the bone. Thus, the sample for comparison was necessarily incomplete in these cases.

3. Characters proposed by Ezcurra and Agnolin (2012) Ezcurra and Agnolin (2012) identified four characters of MB R. 2351 as ‘unambiguous abelisauroid synapomorphies’. The morphology of these characters, their expression in the specimen and their distribution within theropod dinosaurs are discussed in the following.

Fig. 1. Distal end of left tibia of a small theropod dinosaur from the Middle Jurassic of Stonesfield, England (MB R. 2351), in anterior (A, stereophotographs), medial (B), lateral (C, stereophotographs), distal (D, stereophotographs), and posterior (E) views. Abbreviations. d, longitudinal depression that defines the elevated area within the facet for the ascending process of the astragalus; e, eroded surface of the lateral malleolus; lm, lateral malleolus; mb, medial bulge; r, ridge that separates the facet for the contact with the fibula from the anterior side of the distal tibia. Scale bar is 25 mm.

O.W.M. Rauhut / Proceedings of the Geologists’ Association 123 (2012) 779–786

781

3.1. Vertical facet for the reception of the ascending process of the astragalus In theropods ancestrally, a small, triangular ascending process of the astragalus slots into the distal end of the tibia. Thus, an oblique step is present on the anterior side of the distal end of the tibia in basal theropods, extending from the mediodistal corner of the anterior side lateroproximally. This step is pronounced and set at a low angle of 20–308 in respect to the transverse axis of the distal end in basal theropods, such as coelophysids (e.g. Raath, 1977) and Dilophosaurus (Welles, 1984). In averostran theropods, the morphology of this step is somewhat more complex, due to an anteroproximal expansion of the astragalar condyles and a change in morphology of the astragalar ascending process, from a triangular, block-like process to a higher, more laminar structure, which, in basal averostrans, is restricted to the lateral side of the astragalus (Welles and Long, 1974; Rauhut, 2003). Thus, in contrast to the situation in basal theropods, the ascending process is more distinctly offset from the medial side of the proximal rim of the anterior side of the astragalar body, resulting in a concave kink in this rim. Consequently, the step on the anterior side of the distal tibia is somewhat offset proximally from the distal end to accommodate the anteroproximal expansion of the distal condyles of the astragalus, and there is a distinct flexure in the step at the point where the ascending process of the astragalus begins, so that the lateral part of this step is considerably more steeply inclined than the medial part. This is the situation in most basal tetanurans, but also in a number of ceratosaurs. In one of the basalmost coelurosaurs known, the Chinese Tugulusaurus, the step is considerably lower than in basal tetanurans and its medial part is absent or very small (Rauhut and Xu, 2005). Here, the remaining ridge that borders the ascending process of the astragalus medially is very steeply inclined, almost vertical. In coelurosaurian theropods in which the distal end of the tibia is not articulated with the astragalus (Fig. 2; e.g. Coelurus, YPM 2010; Galton and Molnar, 2005; ‘Stokesosaurus’ langhami [which is currently being referred to its own genus; Brusatte and Benson, in press], OUMNH J.3311; Benson, 2008; Gallimimus; Brusatte, pers. comm., 2012; Falcarius, UMNH VP 12362; Zanno, 2010) and a few other taxa,

Fig. 2. Anterior side of the distal end of the left tibia in the coelurosaurian theropods Falcarius (A and B) and Stokesosaurus (C) in anterior (A and C) and distal (B) views. Abbreviations as in Fig. 1, and: mr, median ridge within the facet for the ascending process of the astragalus. Scale bars are 50 mm. Photos of Falcarius courtesy Lindsay Zanno, photo of Stokesosaurus courtesy Roger Benson.

Fig. 3. Anterior side of the distal end of a left tibia referred to the neovenatorid Aerosteon (MCNA PV 3139). Abbreviations as in Figs. 1 and 2, and: asc, fragment of the ascending process of the astragalus preserved in articulation with the tibia. Scale bar is 50 mm.

such as the neovenatorids Austrovenator (Hocknull et al., 2009) and a tibiotarsus referred to Aerosteon (MCNA PV 3139; Sereno et al., 2008; Benson et al., 2010; Fig. 3), the typical oblique step on the anterior side of the distal tibia is absent, since the ascending process is further expanded into a high sheet of bone that arises out of the entire breadth of the astragalar body (Rauhut, 2003). A low, vertical ridge or bulge might still be present on the medial edge of the anterior side in these taxa, and a low ridge is often present on the lateral side as well, demarcating the facet for the ascending process from the facet for the contact with the fibula. This condition is also present in some taxa for which the ascending process of the astragalus is not known, such as the basal tetanurans Chilantaisaurus (Benson and Xu, 2008) and Chuandongocoelurus (CCG 20010; Fig. 4), and the spinosaurid Suchomimus (MNN GDF 500). The noasaurid Velocisaurus also seems to have a similar condition (Bonaparte, 1991b; Novas, 2009: Fig. 16.8b; Ezcurra and Agnolin, 2012: Fig. 3D). In MB R. 2351, there is a rounded bulge medially on the anterior side of the distal end of the tibia that accounts for approximately 20–23% of the transverse width of the distal end (Fig. 1). Its distal part is largely abraded, but proximally, an almost vertical margin for the ascending process of the astragalus is defined by its lateral rim. This margin lowers gradually towards the facet for the ascending process and is not abruptly offset from it, in contrast to the situation in some other taxa, where this border is pronounced (e.g. Rauhut, 2005: Fig. 5d). It might be noted that, although Ezcurra and Agnolin (2012: Fig. 1B) figured the facet for the ascending process as expanding in the proximal part, this is an artefact created by the abrasion of the distal part of the medial bulge.

Fig. 4. Distal end of the right tibia (reversed for comparison) of the small basal tetanuran Chuandongocoelurus (CCG 20010) in anterior (A, stereophotographs) and distal (B) views. Abbreviations as in Figs. 1 and 2. Scale bar is 25 mm.

782

O.W.M. Rauhut / Proceedings of the Geologists’ Association 123 (2012) 779–786

3.2. Sub-rectangular anterior scar of the astragalar ascending process in the distal end of tibia This character is clearly related to the character noted above. In most basal theropods, the ascending process of the astragalus slopes lateroproximally, resulting in a more or less triangular facet on the distal tibia (see above). However, in those taxa that have a proximally expanded ascending process, the medial rim of the facet is consequently more steeply inclined, and can be vertical (see above). Likewise, the ridge delimitating the anterior side of the distal tibia from the facet for the fibula is also steeply inclined and often subvertical (Figs. 1A and 2A), thus giving the impression of a rectangular facet on the anterior side of the distal end of the tibia, though the two ridges are still slightly converging proximally in many taxa (e.g. Velocisaurus, Ezcurra and Agnolin, 2012; Tugulusaurus, Rauhut and Xu, 2005). Thus, this character has a very similar distribution as the first character above. However, since, strictly speaking, only the medial rim of this facet is directly related to the ascending process of the astragalus, whereas the lateral ridge is more defined by the association of the tibia with the fibula, it might be noted that the rectangular (or high triangular) shape of the facet on the anterior tibia does not necessarily directly reflect the shape of the ascending process of the astragalus. In Tugulusaurus, for example, the facet on the distal tibia is trapezoidal and approximately two times as high as wide, whereas the ascending process is triangular and as high as wide or only insignificantly higher (the proximal end is damaged; Rauhut and Xu, 2005). Thus, the direct correlation of a rectangular facet on the tibia with a more or less rectangular ascending process of the astragalus, as argued by Ezcurra and Agnolin (2012), is problematic. In MB R. 2351, there is a pronounced ridge laterally that separates the anterior side of the distal tibia from the anterolateral facet for the fibula (Fig. 1A). This ridge extends proximally and very slightly medially and is very slightly concave. It thus converges proximally upon the medial buttress for the ascending process of the astragalus described above; whereas these two structures are 18 mm apart distally, their distance at the proximal end of the medial bulge, some 26 mm above the distal end, is 13 mm. Furthermore, in contrast to the interpretative drawing of Ezcurra and Agnolin (2012: Fig. 1B), there is no clearly defined, oblique proximal ridge delimiting the facet on the distal tibia, but the facet rather fades out proximally, with the lateral and medial margins becoming more strongly converging proximally, as in most coelurosaurs. Thus, the facet has subparallel margins, but cannot be regarded as strictly rectangular. 3.3. Median vertical ridge in the scar of the ascending process of the astragalus A faint ridge within the facet for the ascending process of the astragalus on the anterior side of the distal tibia was first described by Long and Molnar (1998) in the poorly preserved type tibia of the Middle Jurassic Australian theropod Ozraptor. Similar ridges were later described for two small theropod tibiae from the Late Jurassic of Tendaguru, Tanzania (Rauhut, 2005), the small noasaurid Velocisaurus (Novas, 2009; Ezcurra et al., 2010; Ezcurra and Agnolin, 2012) and the poorly known Austrocheirus (Ezcurra et al., 2010), and Ezcurra et al. (2010) and Ezcurra and Agnolin (2012) considered this character to be a synapomorphy of abelisauroids. The exact morphology of the vertical ridge within the facet for the ascending process of the astragalus is variable. In Ozraptor, a thin, faint ridge is present that extends all the way proximally to the end of the facet (Long and Molnar, 1998: Fig. 2B and 3A). In the better preserved tibia described and figured by Rauhut (2005: Fig. 5d), the ridge is broader, but restricted to the distal half of the facet,

fading out proximally (note that the ridge is exaggerated in the stereophotographs provided by Rauhut and is less conspicuous in reality). In Velocisaurus, the ridge seems to be very faint and broad and extends to the proximal end of the facet (Novas, 2009: Fig. 6.18B), though it was figured as less broad and restricted to the distal half of the facet by Ezcurra and Agnolin (2012: Fig. 3D). Finally, in Austrocheirus, only the abraded base of a seemingly broad ridge is present (Ezcurra et al., 2010: Fig. 4A and B). In MB R. 2351 the ‘ridge’ is mainly defined by a faint step within the medial part of the astragalar facet, but there is no clear definition of a lateral rim of this structure (Fig. 1A). Thus, the ‘ridge’ is better regarded as a very slightly elevated area within the facet that gradually lowers laterally, and it is mainly defined by a shallow longitudinal depression within the facet for the ascending process medially (Fig. 1A and D). A vertical ridge or a slightly elevated area within the facet on the anterior side of the distal tibia is also found in other taxa. The tibia of Chuandongocoelurus (CCG 20010; Fig. 4) has a broad, faint swelling that extends over the entire height of the facet and is mainly defined by a longitudinal depression medially, and welldeveloped vertical ridges are present in the tibia referred to Aerosteon (MCNA PV 3139; Fig. 3) and the basal tyrannosauroid ‘Stokesosaurus’ langhami (Fig. 2C; Benson, 2008: Fig. 12A), also extending over the entire height of the facet. Faint ridges or elevated areas seem to be present in a number of other coelurosaurs (e.g. Nedcolbertia, Kirkland et al., 1998; Gallimimus, Brusatte, pers. comm., 2012; Falcarius, UMNH VP 12362; Fig. 2A and B; Rahonavis, UA 8656), in which they are mainly defined by a longitudinal depression medially, as in MB R. 2351. However, the exact distribution of the character within this clade is difficult to evaluate, since coelurosaur tibiae are frequently found in articulation with the proximal tarsals. Furthermore, there seems to be considerable variation in the development of this morphology, from faintly elevated, broad areas to more clearly defined vertical ridges, making its systematic utility problematic. It might be noted that Ezcurra and Agnolin (2012) cite Rauhut (2005) as the original source for this character as an abelisauroid synapomorphy. In fact, however, the latter paper suggested the presence of a broad ridge or bulge medial to the facet for the ascending process of the astragalus as a possible synapomorphy of abelisauroids, or a more restricted subclade. Nevertheless, this character has a wider distribution than recognized by Rauhut (2005), so that this interpretation is questionable (see below). A median ridge within the astragalar facet was described by Rauhut (2005) for the small tibiae from Tendaguru and suggested as a character that these elements share with the poorly known Middle Jurassic Australian theropod Ozraptor (Long and Molnar, 1998). However, this character had not been described in any other theropod at that time, so that it was not considered to be an abelisauroid synapomorphy, and its broader distribution outlined above invalidates Rauhut’s assessment of this character as a potential synapomorphy of Ozraptor and the Tanzanian tibiae. 3.4. Posterolateral process of tibia not sharply offset from the lateral margin of the shaft This character was proposed as a synapomorphy shared between MB R. 2351 and abelisauroids, but no clear definition of how the condition in these animals differs from that in other theropods was given, other than that the posterolateral process is poorly developed. The presence of a posterolateral process (=lateral malleolus) of the distal tibia that is set off laterally from the tibial shaft is a synapomorphy of neotheropods (Rauhut, 2003; Nesbitt et al., 2007). In basal taxa, it is developed as a small posterolateral flange that extends slightly beyond the anterior edge of the step

O.W.M. Rauhut / Proceedings of the Geologists’ Association 123 (2012) 779–786

bordering the ascending process. In these taxa, it is typically offset from the lateral margin of the tibial shaft by a small, angular expansion and has a straight lateral margin (e.g. Ezcurra and Novas, 2007: Fig. 11A and B). It backs the distal end of the fibula only partially posteriorly and achieves a first, though limited contact with the calcaneum distally. In averostrans, the distal tibia is further expanded transversely, completely backs the fibula posteriorly and forms a broad contact with the calcaneum distally. However, although the distal end of the tibia is thus generally broadened and expanded from the shaft in this clade, resulting in a triangular outline in distal view, the lateral malleolus shows a variable development. In a number of taxa, including Velocisaurus (Novas, 2009: Fig. 6.18B), Sinraptor (Currie and Zhao, 1994: Fig. 22H and K), Stokesosaurus (OUMNHJ.3311; Fig. 2C), and, probably, Elaphrosaurus (MB R. dd unnumbered; the lateral edge of the malleolus is damaged in this taxon), the general outline is similar to that seen in basal theropods, in that the malleolus has an angular proximal end and a straight lateral margin. In several coelurosaurs, such as Coelurus (Galton and Molnar, 2005), Albertonykus (Longrich and Currie, 2009), Falcarius (UMNH VP 12362; Fig. 2A; Zanno, 2010), Erliansaurus (Xu et al., 2002), and Utahraptor (Kirkland et al., 1993), the lateral malleolus expands gradually and moderately from the tibial shaft, but has a small, thin, rounded lateral expansion at its distal end. Many averostran theropods, finally, have the lateral malleolus gradually expanding from the tibial shaft, with a slightly concave to rounded lateral margin. In these cases, the malleolus can be indistinct, as e.g. in Eustreptospondylus (Sadleir et al., 2008) and many coelurosaurs (Rahonavis, UA 8656; Deinonychus, Ostrom, 1969; Juravenator, JME Sch 200, Chiappe and Go¨hlich, 2010), slightly to moderately expanded, as in Ceratosaurus (Madsen and Welles, 2000), Chuandongocoelurus (CCG 20010; Fig. 4A), many basal tetanurans, and many coelurosaurs, or strongly laterally and distally expanded, as in Majungasaurus (Carrano, 2007), Quilmesaurus (Jua´rez-Valieri et al., 2007), Torvosaurus (Britt, 1991), and most carcharodontosaurs (e.g. Neovenator, Brusatte et al., 2008; Mapusaurus, Coria and Currie, 2006). Masiakasaurus seems to present an intermediate state between the angular malleolus with straight margin (as in Velocisaurus) and a moderately expanded, rounded malleolus (Carrano et al., 2002: Fig. 15F). The morphology of the lateral malleolus in MB R. 2351 seems to correspond to the last category, of a malleolus that gradually expands from the shaft (Fig. 1A and E). It is furthermore only indistinctly developed, similar to the condition seen in Eustreptospondylus and many coelurosaurs. However, the distal end of the lateral side of the tibia is abraded to partially expose the spongiosa (Fig. 1C), so it cannot be ruled out that a small lateral expansion at the distal end might have been present, as in some coelurosaurs. Regardless of whether such an expansion is present, it is clear that, in contrast to the proposal of Ezcurra and Agnolin (2012), the shape of the lateral malleolus of MB R. 2351 differs from the angular malleolus seen in Velocisaurus, the more strongly expanded structure in Masiakasaurus, and notably from the very strongly expanded malleolus in abelisaurids, and it is more comparable to the situation in certain tetanurans. 4. Morphology of the distal tibia in abelisauroids Apart from the exact morphology of the characters described above and their occurrence in other theropod groups, one key question is whether these features can be regarded as abelisauroid synapomorphies, as argued by Ezcurra and Agnolin (2012). In the basal ceratosaur Ceratosaurus, which represents the immediate outgroup to abelisauroids, the distal tibia has a welldeveloped oblique step on the anterior side of its distal end, bracing the low and triangular ascending process of the astragalus

783

proximomedially (Gilmore, 1920; Madsen and Welles, 2000). Since all known specimens of Ceratosaurus have the proximal tarsals preserved in articulation with the tibia, nothing can be said about the probable presence or absence of a vertical ridge on the facet for the ascending process. As noted above, the medial malleolus is gradually expanded from the tibial shaft and moderately developed. Abelisaurids have a similar, though somewhat modified morphology. In Rajasaurus (Wilson et al., 2003), Majungasaurus (Carrano, 2007), Pycnocnemosaurus (Kellner and Campos, 2002), and Quilmesaurus (Jua´rez-Valieri et al., 2007) the tibia is not preserved in articulation with the proximal tarsals, and thus the morphology of the anterior side can be established in detail. These taxa have a well-developed, triangular facet for the ascending process of the astragalus, with a low-angled proximomedial margin. There is no vertical ridge in the facet for the ascending process and the medial malleolus arises gradually out of the tibial shaft and is strongly laterally and distally expanded. The astragalus of Majungasaurus has a low, very slender, tongue-shaped ascending process that is restricted to the lateral half of the astragalar body. In Ekrixinatosaurus and Skorpiovenator, the proximal tarsals are preserved in articulation with the tibia (Calvo et al., 2004; Canale et al., 2009). The same is true for Aucasaurus (Coria et al., 2002), but the distal tibia of this taxon has not been described or figured in detail yet. Canale et al. (2009) noted a subrectangular ascending process of the astragalus as an ambiguous synapomorphy of a clade uniting the latter abelisaurids, together with the genera Carnotaurus and Ilokelesia. In Skorpiovenator, the ascending process has an unusual, trapezoidal outline, with a proximal medial expansion (Canale et al., 2009). In Ekrixinatosaurus, the ascending process is small, with subparallel margins, but rounded proximally (Calvo et al., 2004; Jua´rez-Valieri et al., 2007). The lateral malleolus in Ekrixinatosaurus seems to have a very similar shape to the other abelisaurids noted above. The morphology of the distal tibia and the shape of the ascending process of the astragalus in noasaurids are poorly known. In Masiakasaurus, the ascending process is relatively considerably higher than in abelisaurids and trapezoidal in outline (Carrano et al., 2002: Fig. 16). The distal tibia of this taxon is flat and does not seem to exhibit a well-developed, clearly defined facet for the ascending process of the astragalus (Carrano et al., 2002: Fig. 15F). Velocisaurus shows a broad, subrectangular facet on the anterior side of the distal tibia, but the ascending process of the astragalus is unknown (Bonaparte, 1991b; Novas, 2009). The facet is bound medially by a vertical ridge and has a faint vertical ridge within the facet. As noted above, the lateral malleolus in Velocisaurus is angular, whereas Masiakasaurus has an intermediate morphology between an angular and a moderately expanded, rounded malleolus. Thus, on the basis of this short survey, the characters noted by Ezcurra and Agnolin (2012) seem to have a very restricted distribution within well-established abelisauroid taxa, with Velocisaurus being the only taxon exhibiting all of them (whereas the presence of all or most of the characters seems to be the norm in coelurosaurs; see above). Thus, these characters can hardly been regarded as unambiguous abelisauroid synapomorphies. It might be noted that Rauhut (2011, p. 209) suggested a further character in the distal tibia to represent a synapomorphy of ceratosaurs or a subclade thereof, a depression in the distal articular end of the tibia. In MB R. 2351, the distal end is largely abraded, but a matrix-filled spot in the distal surface of the tibia (Fig. 1C) seems to correspond to such a depression. However, although Rauhut (2011, p. 209) noted that this character ‘‘is not found in any nonceratosaurian theropod’’, it is indeed present in at least Dilophosaurus (UCMPV 6468) and Falcarius (Fig. 2B) outside

784

O.W.M. Rauhut / Proceedings of the Geologists’ Association 123 (2012) 779–786

ceratosaurs, so the distribution of this depression needs further evaluation. The argument presented by Ezcurra and Agnolin (2012) was based mainly on the morphology of the distal tibia of the taxa Ozraptor, Velocisaurus and Austrocheirus, with some additional data from Masiakasaurus and other abelisauroids. Thus, the systematic position of the first three taxa is key for this argument. Although represented only by a partial hindlimb and foot, Velocisaurus is the best known of these taxa (Bonaparte, 1991b). Several phylogenetic analyses support abelisauroid and, more specifically, noasaurid relationships for this genus (Carrano and Sampson, 2008; Canale et al., 2009), mainly supported by apomorphic characters of the foot, such as the antarctometatarsal metatarsus with a strongly reduced metatarsal II. However, more complete material would, of course, help to establish the systematic affinities of Velocisaurus more precisely. The referral of Ozraptor to the Abelisauroidea was first suggested by Rauhut (2005), in an article that was mainly concerned with the systematic position of three isolated, small tibiae from the Late Jurassic of Tendaguru, Tanzania. Rauhut (2005) concluded that two of these tibiae (MB R. 1750, MB R. 1751) represent abelisauroid theropods. However, this conclusion was not solely based on the morphology of the distal tibia, but on the combination of characters expressed by these complete elements. Rauhut (2005, p. 102) argued that these tibiae lacked two tetanuran synapomorphies, a fibular condyle that is offset from the cnemial crest by a strongly developed incisura tibialis and a strongly developed fibular crest that is offset from the proximal end, and thus cannot be referred to Tetanurae. The referral to Abelisauroidea was then based on the observation that, within non-tetanuran theropods, a flat anterior side of the distal tibia is only found in the small abelisauroids Velocisaurus and Masiakasaurus. Furthermore, Rauhut (2005, p. 102) suggested that the presence of a well-developed vertical ridge or bulge medial to the facet for the ascending process of the astragalus might represent an abelisauroid synapomorphy, paralleled by some tetanurans. The suggested referral of Ozraptor to the Abelisauroidea was then based on details of the morphology of the anterior side of the distal end of the tibia shared between the type specimen of this taxon and MB R. 1750, namely the presence of a depressed, subdivided facet for the ascending process of the astragalus. However, as noted above, these characters are also present in a number of other theropod taxa, including several neovenatorids and coelurosaurs. Thus, these features alone are not sufficient to refer Ozraptor to the Abelisauroidea. The further character noted by Rauhut (2005), the presence of a vertical ridge or bulge medial to the astragalar facet, is also not unique to abelisauroids, but present in the basal tetanuran Chuandongocoelurus (CCG 20010; Fig. 4), neovenatorids (Chilantaisaurus, IVPP V 2884, Benson and Xu, 2008; tibia referred to Aerosteon, MCNA PV 3139; Fig. 3), and coelurosaurs (Coelurus, Galton and Molnar, 2005; Stokesosaurus langhami, Fig. 2C; Benson, 2008; Falcarius, Fig. 2A and B; Zanno, 2010; Albertonykus, Longrich and Currie, 2009). Thus, Ozraptor cannot be referred to Abelisauroidea with any certainty and should be regarded as Theropoda indet (see also Carrano and Sampson, 2008). Austrocheirus is based on extremely fragmentary theropod remains from the Late Cretaceous of Santa Cruz, Argentina (Ezcurra et al., 2010). The material comprises caudal vertebral fragments, a supposed partial metacarpal, poorly preserved distal tibia, metatarsal fragments, and partial phalanges. Referral of this taxa to the Abelisauroidea was based on the morphology of the distal end of the tibia, with the referral to Ceratosauria being supported by several characters of metacarpal III and one character each of the manual phalanges and metatarsal III (Ezcurra et al., 2010, p. 13). However, the phylogenetic analysis presented by Ezcurra et al. (2010) only included four non-ceratosaurian taxa, one of them

representing the outgroup. Most importantly, no neovenatorid or coelurosaurian taxon was included, both groups that share many of the tibial characters, as noted above. Furthermore, the elements identified as metacarpal III and manual phalanx are very poorly preserved. The alleged metacarpal III differs from the same element in all other theropods (including ceratosaurs; Gilmore, 1920; Burch and Carrano, 2012) in the outline of the cross-section of the shaft and the morphology of the distal end; the proximal end is not preserved. Thus, there seems to be little evidence to support this identification. The same is true for the supposed manual phalanx; the element is missing its dorsal side and both articular ends are largely abraded. Thus, it cannot be excluded that this might be a pedal phalanx of digit IV, which tend to be short and stocky. This leaves the low distal articular end of metatarsal III that is not offset from the shaft as the only possible ceratosaurian synapomorphy. However, this character is widespread within coelurosaurs (e.g. Kobayashi and Barsbold, 2005; Turner et al., 2009), so it cannot be regarded as a ceratosaurian synapomorphy. Thus, there seems to be little evidence for a referral of Austrocheirus to the Abelisauroidea, and this taxon should be regarded as Theropoda indet. In summary, the characters noted by Ezcurra and Agnolin (2012) cannot be regarded as abelisauroid synapomorphies, nor are they even common in that clade. Thus, there is little evidence for a referral of MB R. 2351 to the Abelisauroidea. 5. Discussion As outlined above, the characters used by Ezcurra and Agnolin (2012) cannot be regarded as abelisauroid synapomorphies and there is no reason to consider MB R. 2351 to represent the oldest representative of the Abelisauroidea in the northern Hemisphere. All of the characters expressed in this specimen are present in coelurosaurian theropods, and since coelurosaurs are known from roughly contemporaneous beds in England (Rauhut et al., 2010), the specimen might rather represent this clade. However, it must be noted that the characters discussed above are also not unique to coelurosaurs, but are also found in neovenatorids and the basal tetanuran Chuandongocoelurus, so it is best to formally regard MB R. 2351 as Averostra indet. Based on the alleged abelisauroid affinities of MB R. 2351, Ezcurra and Agnolin (2012) argued for an early, global radiation of abelisauroids, followed by a regional extinction of the clade in the northern hemisphere. Other key arguments for this scenario were supposed abelisauroid affinities of the Late Jurassic Chinese taxon Limusaurus and material referred to Elaphrosaurus (also considered to be an abelisauroid by Ezcurra and Agnolin) from the Late Jurassic Morrison Formation of North America (Galton, 1982; Chure, 2001). Limusaurus was considered to be a basal, non-abelisaurian ceratosaur by Xu et al. (2009), but as an abelisauroid by Ezcurra et al. (2010). The taxon has not been included in any other phylogenetic analysis, so its systematic relationships might currently be regarded as uncertain. However, the results of Xu et al. (2009) indicate that Limusaurus represents the sister taxon of Elaphrosaurus, so the phylogenetic relationships of these taxa might be treated together. Originally thought to be a basal ornithomimosaur (Russell, 1972; Galton, 1982), Elaphrosaurus is now generally accepted to be a ceratosaur. Abelisauroid affinities for this taxon were first suggested by Holtz (1994), and this view was supported by Sereno (1997, 1999), Rauhut (2003, 2007), and, most recently, Canale et al. (2009) and Ezcurra et al. (2010). On the other hand, Holtz (2000), Carrano et al. (2002), Sereno et al. (2004), Tykoski and Rowe (2004), and Allain et al. (2007) argued that Elaphrosaurus is a more basal ceratosaur, outside a clade composed of Ceratosaurus and abelisauroids. The latter view was also supported in the most inclusive phylogenetic analyses of

O.W.M. Rauhut / Proceedings of the Geologists’ Association 123 (2012) 779–786

ceratosaurian theropods published so far (Carrano and Sampson, 2008; Pol and Rauhut, in press). Thus, although the latter analyses, which include more ceratosaurian taxa and more characters than other studies, might currently be the best indication of the phylogenetic position of Elaphrosaurus (and, by inference, Limusaurus), the affinities of this taxon are best considered uncertain, pending a detailed re-evaluation of the material (Rauhut and Carrano, in preparation). The material referred to Elaphrosaurus from the Morrison Formation of the western USA consists of a humerus (Galton, 1982) and a proximal end of a tibia (Chure, 2001). Although both specimens might represent ceratosaurs, none of them can be referred to Elaphrosaurus with any certainty (Rauhut and Carrano, in preparation), so they are best considered cf. Ceratosauria indet. In summary, there is currently no secure evidence for the presence of abelisauroids in the northern hemisphere prior to the occurrence of Genusaurus in the Albian of France (Accarie et al., 1995). Although the scenario presented by Ezcurra and Agnolin (2012) remains possible, depending on the phylogenetic position of Limusaurus (the only possible Laurasian Jurassic abelisauroid if the material from the Morrison Formation is not taken into consideration), it is currently equally likely that abelisauroids were restricted to the southern hemisphere in the Jurassic, and their apparent rarity simply reflects the poor Jurassic dinosaur fossil record of Gondwana (Rauhut and Lo´pez-Arbarello, 2008; Pol and Rauhut, in press). A solution of this problem can only come from new discoveries and detailed re-evaluations of key taxa, such as Elaphrosaurus and Limusaurus. However, the tibia fragment MB R. 2351 from Stonesfield cannot help in this matter. Acknowledgments I thank Oliver Wings for the rapid and bureaucracy-free loan of MB R. 2351. Lindsay Zanno and Roger Benson provided detailed photographs of the tibiae of Falcarius and Stokesosaurus langhami, respectively, for which I am most grateful. Adriana Lo´pezArbarello, Roger Benson and Steve Brusatte are thanked for critical comments on the manuscript. This study was supported by grant I/ 84 640 by the Volkswagen Foundation. References Accarie, H., Beaudoin, B., Dejax, J., Frie`s, G., Michard, J.-G., Taquet, P., 1995. De´couverte d’un Dinosaure The´ropode nouveau (Genusaurus sisteronis n. g., n. sp.) dans l’Albien marin de Sisteron (Alpes de Haute-Provence, France) et extension au Cre´tace´ infe´rieur de la ligne´e ce´ratosaurien. Comptes Rendus de l’Academie des Sciences Paris II 320, 327–334. Allain, R., Tykoski, R.S., Aquesbi, N., Jalil, N.-E., Monbaron, M., Russell, D.A., Taquet, P., 2007. An abelisauroid (Dinosauria: Theropoda) from the Early Jurassic of the High Atlas Mountains, Morocco, and the radiation of ceratosaurs. Journal of Vertebrate Paleontology 27, 610–624. Benson, R.B.J, 2008. New information on Stokesosaurus, a tyrannosauroid (Dinosauria: Theropoda) from North America and the United Kingdom. Journal of Vertebrate Paleontology 28, 732–750. Benson, R.B.J., 2009. An assessment of variability in theropod dinosaur remains from the Bathonian (MIddle Jurassic) of Stonesfield and New Park Quarry, UK and taxonomic implications for Megalosaurus bucklandii and Iliosuchus incognitus. Palaeontology 52, 857–877. Benson, R.B.J., 2010. A description of Megalosaurus bucklandii (Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods. Zoological Journal of the Linnean Society 158, 882–935. Benson, R.B.J., Carrano, M.T., Brusatte, S.L., 2010. A new clade of archaic large-bodied predatory dinosaurs (Theropoda: Allosauroidea) that survived to the latest Mesozoic. Naturwissenschaften 97, 71–78. Benson, R.B.J., Xu, X., 2008. The anatomy and systematic position of the theropod dinosaur Chilantaisaurus tashuikouensis Hu, 1964 from the Early Cretaceous of Alanshan, People’s Republic of China. Geological Magazine 145, 778–789. Bonaparte, J.F., 1991a. The Gondwanian theropod families Abelisauridae and Noasauridae. Historical Biology 5, 1–25. Bonaparte, J.F., 1991b. Los vertebrados fosiles de la Formacion Rio Colorado, de la ciudad de Neuquen y Cercanias, Cretacio superior, Argentina. Revista del Museo de Ciencias Naturales – Bernardino Rivadavia 4, 15–123.

785

Bonaparte, J.F., Novas, F.E., 1985. Abelisaurus comahuensis, n. g., n. sp., Carnosauria del Cretacio tardio de Patagonia. Ameghiniana 21, 259–265. Britt, B.B., 1991. Theropods of Dry Mesa Quarry (Morrison Formation, Late Jurassic), Colorado, with emphasis on the osteology of Torvosaurus tanneri. Brigham Young University Geology Studies 37, 1–72. Brusatte, S.L., Benson, R.B.J. The systematics of Late Jurassic tyrannosauroids (Dinosauria: Theropoda) from Europe and North America. Acta Palaeontologica Polonica, in press. Brusatte, S.L., Benson, R.B.J., Hutt, S., 2008. The osteology of Neovenator salerii (Dinosauria: Theropoda) from the Wealden Group (Barremian) of the Isle of Wight. Monograph of the Palaeontographical Society 631, 1–75. Burch, S.H., Carrano, M.T., 2012. An articulated pectoral girdle and forelimb of the abelisaurid theropod Majungasaurus crenatissimus from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology 32, 1–16. Calvo, J.O., Rubilar-Rogers, D., Moreno, K., 2004. A new Abelisauridae (Dinosauria: Theropoda) from northwestern Patagonia. Ameghiniana 41, 555–563. Canale, J.I., Scanferla, C.A., Agnolin, F.L., Novas, F.E., 2009. New carnivorous dinosaur from the Late Cretaceous of NW Patagonia and the evolution of abelisaurid theropods. Naturwissenschaften 96, 409–414. Carrano, M.T., 2007. The appendicular skeleton of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. Society of Vertebrate Paleontology, Memoir 8, 163–179. Carrano, M.T., Sampson, S.D., 2008. The phylogeny of Ceratosauria (Dinosauria: Theropoda). Journal of Systematic Palaeontology 6, 183–236. Carrano, M.T., Sampson, S.D., Forster, C.A., 2002. The osteology of Masiakasaurus knopfleri, a small abelisauroid (Dinosauria: Theropoda) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology 22, 510–534. Chiappe, L.M., Go¨hlich, U.B., 2010. Anatomy of Juravenator starki (Theropoda: Coelurosauria) from the Late Jurassic of Germany. Neues Jahrbuch fu¨r Geologie und Pala¨ontologie, Abhandlungen 258, 257–296. Chure, D.J., 2001. The second record of the African theropod Elaphrosaurus (Dinosauria, Ceratosauria) from the Western Hemisphere. Neues Jahrbuch fu¨r Geologie und Pala¨ontologie, Monatshefte 2001, 565–576. Coria, R.A., Chiappe, L.M., Dingus, L., 2002. A new close relative of Carnotaurus sastrei Bonaparte 1985 (Theropoda: Abelisauridae) from the Late Cretaceous of Patagonia. Journal of Vertebrate Paleontology 22, 460–465. Coria, R.A., Currie, P.J., 2006. A new carcharodontosaurid (Dinosauria, Theropoda) from the Upper Cretaceous of Argentina. Geodiversitas 28, 71–118. Currie, P.J., Zhao, X.-J., 1994. A new carnosaur (Dinosauria, Theropoda) from the Jurassic of Xinjiang, People’s Republic of China. Canadian Journal of Earth Sciences 30, 2037–2081. Ezcurra, M.D., Agnolin, F.L., 2012. An abelisauroid dinosaur from the Middle Jurassic of Laurasia and its implications on theropod palaeobiogeography and evolution. published online In: Proceedings of the Geologists’ Association, http:// dx.doi.org/10.1016/j.pgeola.2011.1012.1003. Ezcurra, M.D., Agnolin, F.L., Novas, F.E., 2010. An abelisauroid dinosaur with a nonatrophied manus from the Late Cretaceous Pari Aike Formation of southern Patagonia. Zootaxa 2450, 1–25. Ezcurra, M.D., Novas, F.E., 2007. Phylogenetic relationships of the Triassic theropod Zupaysaurus rougieri from NW Argentina. Historical Biology 19, 35–72. Galton, P.M., 1982. Elaphrosaurus, an ornithomimid dinosaur from the Upper Jurassic of North America and Africa. Pala¨ontologische Zeitschrift 56, 265–275. Galton, P.M., Molnar, R.E., 2005. Tibiae of small theropod dinosaurs from southern England. From the Middle Jurassic of Stonesfield near Oxford and the Lower Cretaceous of the Isle of Wight. In: Carpenter, K. (Ed.), The Carnivorous Dinosaurs. Indiana University Press, Bloomington/Indianapolis, pp. 3–22. Gilmore, C.W., 1920. Osteology of the carnivorous Dinosauria in the United States National Museum, with special reference to the genera Antrodemus (Allosaurus) and Ceratosaurus. Bulletin of the United States National Museum 110, 1–154. Hocknull, S.A., White, M.A., Tischler, T.R., Cook, A.G., Calleja, N.D., Sloan, T., Elliott, D.A., 2009. New mid-Cretaceous (latest Albian) dinosaurs from Winton, Queensland, Australia. PLoS One 4, 1–51. Holtz Jr., T.R., 1994. The phylogenetic position of the Tyrannosauridae: implications for theropod systmatics. Journal of Paleontology 68, 1100–1117. Holtz Jr., T.R., 2000. A new phylogeny of the carnivorous dinosaurs. Gaia 15, 5–61. Jua´rez-Valieri, R.D., Fiorelli, L.E., Cruz, L.E., 2007. Quilmesaurus curriei Coria, 2001 (Dinosauria, Theropoda). Su validez taxono´mica y relaciones filogene´ticas. Revista del Museo Argentino de Ciencias Naturales 9, 59–66. Kellner, A.W.A., Campos, D.A., 2002. On a new theropod dinosaur (Abelisauria) from the continental Cretaceous of Brazil. Arquivos do Museu Nacional 60, 163–170. Kirkland, J.I., Britt, B.B., White, C.H., Madsen, S.K., Burge, D.L., 1998. A small coelurosaurian theropod from the Yellow Cat Member of the Cedar Mountain Formation (Lower Cretaceous, Barremian) of eastern Utah. New Mexico Museum of Natural History and Science Bulletin 14, 239–248. Kirkland, J.I., Burge, D., Gaston, R., 1993. A large dromaeosaur (Theropoda) from the Lower Cretaceous of eastern Utah. Hunteria 2, 1–16. Kobayashi, Y., Barsbold, R., 2005. Reexamination of a primitive ornithomimosaur, Garudimimus brevipes Barsbold, 1981 (Dinosauria: Theropoda), from the Late Cretaceous of Mongolia. Canadian Journal of Earth Sciences 42, 1501–1521. Long, J.A., Molnar, R.E., 1998. A new Jurassic theropod dinosaur from western Australia. Records of the Western Australian Museum 19, 121–129. Longrich, N.R., Currie, P.J., 2009. Albertonykus borealis, a new alvarezsaur (Dinosauria: Theropoda) from the Early Maastrichtian of Alberta, Canada: implications for the systematics and ecology of the Alvarezsauridae. Cretaceous Research 30, 239–252.

786

O.W.M. Rauhut / Proceedings of the Geologists’ Association 123 (2012) 779–786

Madsen, J.H.J., Welles, S.P., Ceratosaurus (Dinosauria, Theropoda). A revised osteology. Miscellaneous Publications, Utah Geological Survey 00-2, 2000, pp. 1–80. Maganuco, S., Cau, A., Dal Sasso, C., Pasini, G., 2007. Evidence of large theropods from the Middle Jurassic of the Mahajanga Basin, NW Madagascar, with implications for ceratosaurian pedal ungual evolution. Atti della Societa` Italiana di Scienze Naturali e del Museo Civico di Storia Naturale – Milano 148, 261–271. Maganuco, S., Cau, A., Pasini, G., 2005. First description of theropod remains from the Middle Jurassic (Bathonian) of Madagascar. Atti della Societa` Italiana di Scienze Naturali e del Museo Civico di Storia Naturale – Milano 146, 165–202. Mateus, O., Walen, A., Antunes, M.T., 2006. The large theropod fauna of the Lourinha Formation (Portugal) and its similarity to that of the Morrison Formation, with a description of new species of Allosaurus. New Mexico Museum of Natural History and Science Bulletin 36, 123–129. Nesbitt, S.J., Irmis, R.B., Parker, W.G., 2007. A critical re-evaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5, 209–243. Novas, F.E., 2009. The Age of Dinosaurs in South America. Indiana University Press, Bloomington/Indianapolis. Ostrom, J.H., 1969. Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana. Peabody Museum of Natural History Bulletin 30, 1–165. Pol, D., Rauhut, O.W.M. A Middle Jurassic abelisaurid from Patagonia and the early diversification of theropod dinosaurs. Proceedings of the Royal Society of London B, in press. Raath, M.A., 1977. The anatomy of the Triassic theropod Syntarsus rhodesiensis (Saurischia: Podokesauridae) and a consideration of its Biology. Unpublished PhD thesis, Rhodes University, Grahamstown. Rauhut, O.W.M., 2003. The interrelationships and evolution of basal theropod dinosaurs. Special Papers in Palaeontology 69, 1–213. Rauhut, O.W.M., 2005. Postcranial remains of ‘‘coelurosaurs’’ (Dinosauria, Theropoda) from the Late Jurassic of Tanzania. Geological Magazine 142, 97–107. Rauhut, O.W.M., 2007. Elaphrosaurus bambergi Janensch (Dinosauria: Theropoda) from the Upper Jurassic of Tanzania and the evolution of abelisaurs. Ameghiniana 44, 36R. Rauhut, O.W.M., 2011. Theropod dinosaurs from the Late Jurassic of Tendaguru (Tanzania). Special Papers in Palaeontology 86, 195–239. Rauhut, O.W.M., Lo´pez-Arbarello, A., 2008. Archosaur evolution during the Jurassic: a southern perspective. Revista de la Asociacio´n Geolo´gica Argentina 63, 557–585. Rauhut, O.W.M., Milner, A.C., Moore-Fay, S.C., 2010. Cranial osteology and phylogenetic position of the theropod dinosaur Proceratosaurus bradleyi (Woodward, 1910) from the Middle Jurassic of England. Zoological Journal of the Linnean Society 158, 155–195.

Rauhut, O.W.M., Xu, X., 2005. The small theropod dinosaurs Tugulusaurus and Phaedrolosaurus from the Early Cretaceous of Xinjiang, China. Journal of Vertebrate Paleontology 25, 107–118. Russell, D.A., 1972. Ostrich dinosaurs from the Late Cretaceous of western Canada. Canadian Journal of Earth Sciences 9, 375–402. Sadleir, R., Barrett, P.M., Powell, H.P., 2008. The anatomy and systematics of Eustreptospondylus oxoniensis, a theropod dinosaur from the Middle Jurassic of Oxfordshire, England. Monograph of the Palaeontographical Society 160, 1–82. Sereno, P.C., 1997. The origin and evolution of dinosaurs. Annual Review of Earth and Planetary Sciences 25, 435–489. Sereno, P.C., 1999. The evolution of dinosaurs. Science 284, 2137–2147. Sereno, P.C., Martinez, R.N., Wilson, J.A., Varricchio, D.J., Alcober, O.A., Larsson, H.C.E., 2008. Evidence for avian intathoracic air sacs in a new predatory dinosaur from Argentina. PLoS One 3, 1–20. Sereno, P.C., Wilson, J.A., Conrad, J.L., 2004. New dinosaurs link southern landmasses in the Mid-Cretaceous. Proceedings of the Royal Society of London B 271, 1325–1330. Soto, M., Perea, D., 2008. A ceratosaurid (Dinosauria, Theropoda) from the Late Jurassic-Early Cretaceous of Uruguay. Journal of Vertebrate Paleontology 28, 439–444. Turner, A.H., Nesbitt, S.J., Norell, M.A., 2009. A large alvarezsaurid from the Late Cretaceous of Mongolia. American Museum Novitas 3648, 1–14. Tykoski, R.S., Rowe, T., 2004. Ceratosauria. In: Weishampel, D.B., Dodson, P., Osmo´lska, H. (Eds.), The Dinosauria. 2nd ed. University of California Press, Berkeley, pp. 47–70. Welles, S.P., 1984. Dilophosaurus wetherilli (Dinosauria, Theropoda). Osteology and comparisons. Palaeontographica A 185, 85–180. Welles, S.P., Long, R.A., 1974. The tarsus of theropod dinosaurs. Annals of the South African Museum 64, 191–218. Wilson, J.A., Sereno, P.C., Srivastava, S., Bhatt, D.K., Khosla, A., Sahni, A., 2003. A new abelisaurid (Dinosauria, Theropoda) from the Lameta Formation (Cretaceous, Maastrichtian) of India, vol. 31. University of Michigan, Contributions from the Museum of Paleontology, pp. 1–42. Xu, X., Clark, J.M., Mo, J., Choiniere, J.N., Forster, C.A., Erickson, G.M., Hone, D.W.E., Sullivan, C., Eberth, D.A., Nesbitt, S.J., Zhao, Q., Hernandez, R., Jia, C., Han, F., Guo, Y., 2009. A Jurassic ceratosaur from China helps to clarify avian digital homologies. Nature 459, 940–944. Xu, X., Zhang, X.-H., Sereno, P., Zhao, X.-J., Kuang, X.-W., Han, J., Tan, L., 2002. A new therizinosauroid (Dinosauria, Theropoda) from the Upper Cretaceous Iren Dabasu Formation of Nei Mongol. Vertebrata PalAsiatica 40, 228–240. Zanno, L.E., 2010. Osteology of Falcarius utahensis (Dinosauria: Theropoda): characterizing the anatomy of basal therizinosaurs. Zoological Journal of the Linnean Society 158, 196–230.