Short Communication a New Large Basal Tetanuran

Journal of Vertebrate Paleontology 29(2):612–615, June 2009 # 2009 by the Society of Vertebrate Paleontology

SHORT COMMUNICATION

A NEW LARGE BASAL TETANURAN (DINOSAURIA: THEROPODA) FROM THE WESSEX FORMATION (BARREMIAN) OF THE ISLE OF WIGHT, ENGLAND

ROGER B. J. BENSON,*,1,2 STEPHEN L. BRUSATTE,3 STEPHEN HUTT4 and DARREN NAISH5; 1Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK, [email protected]; 2Natural History Museum, Cromwell Road, London SW7 5BD, UK; 3Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK, [email protected]; 4 Dinosaur Isle Museum, Culver Parade, Sandown PO36 8QA, UK, [email protected]; 5School of Earth and Environmental Sciences, University of Portsmouth, Burnaby Building, Burnaby Road, Portsmouth PO1 3QL, UK.

The Wessex Formation of the Isle of Wight, southern du Niger, Niamey; PVL, Fundacioń-Instituto Miguel Lillo, Uni- England, has yielded one of the most diverse Early Cretaceous versidad Nacional de Tucumań, Tucumań; UCMP, University of dinosaur assemblages in the world. While isolated theropod California Museum of Paleontology, Berkeley. remains have been known from the Wessex Formation since the 1860s (Fox in Anon., 1866), it is only recently that associated GEOLOGICAL SETTING specimens, and remains representing large-bodied taxa, have been described in the literature. Foremost among these is the MIWG 6350 was collected from the Brighstone Sandstone allosauroid Neovenator salerii, which is represented by approxi- (listed as SS13 by Stewart, 1978) of the Wessex Formation. The mately 70% of the skeleton, making it the most complete large Wessex Formation is the older of two units that together theropod known from Europe (Hutt et al., 1996; Naish et al., comprise the Wealden Group, a Lower Cretaceous (Barremian- 2001; Brusatte et al., in press). Other large-bodied theropods lower Aptian) succession of strata that crop out in the Wessex from the Wessex Formation include the spinosauroid Baryonyx, Sub-basin of both the Isle of Wight and Dorset in southern which is represented by isolated teeth and vertebrae (Martill and England. While the term “Wealden Group” was previously Hutt, 1996; Hutt and Newbery, 2004; Naish and Martill, 2007), applied to the Lower Cretaceous strata of both the Wessex Sub- and the basal tyrannosauroid Eotyrannus lengi, which is known basin and the more northern Weald Sub-basin, we here follow from an associated specimen and referred material that indicates Radley (2004) in restricting the term to the Wessex Formation some individuals obtained large size (Hutt et al., 2001; Naish, and younger Vectis Formation, and in using the term Wealden 2006). Other Wessex Formation theropod remains pertain to Supergroup for the Wealden Group, the Weald Clay Group mostly small-bodied coelurosaurs, and include the enigmatic (Hauterivian-Barremian) of the Weald Sub-basin, and the older taxa Aristosuchus pusillus, Calamosaurus foxi, Ornithodesmus Hastings Beds Group (Berriasian-Valanginian) of the Weald cluniculus, and Thecocoelurus daviesi (Naish et al., 2001), as well Sub-basin. as isolated teeth that have been interpreted as belonging to Within the Wealden Group, the Wessex Formation is overlain dromaeosaurids (Sweetman, 2004). Two large-bodied theropod by the Barremian-Aptian Vectis Formation. The Wessex Forma- taxa, Becklespinax altispinax and Valdoraptor oweni, are known tion is dominated by varicolored clays and sandstones that were from the Hastings Beds Group, of somewhat older age than likely deposited within rivers, oxbow lakes, and ephemeral lakes the Wessex Formation (Berriasian-Valanginian; Naish and on a coastal floodplain (Stewart, 1978). The exposed part of the Martill, 2007). formation is Barremian, and yields nearly all of the dinosaur Here we report remains collected by Keith Simmonds of fossils known from the Isle of Wight (Martill and Naish, 2001). Brighstone from Chilton Chine, Brighstone Bay, Isle of Wight in 1986, that represent an additional large-bodied Wessex For- DESCRIPTION mation theropod (MIWG 6350). Although briefly listed as Ther- Pubis opoda indet. in a table of specimens published by Hutt (2001), MIWG 6350 has not yet been described in the literature. While Two specimens represent portions of the pubes. The first is a this material is highly incomplete, it can be compared with con- proximal fragment of the left pubis, which comprises a portion of temporaneous theropods from the Wessex Formation and other the shaft adjacent to the obturator notch and the base of the Lower Cretaceous units worldwide. It is significant in indicating ischial process (Fig. 1A–D). This fragment indicates that the the presence of a hitherto unrecognized large-bodied theropod pubic shafts were subcylindrical proximally. The posterior sur- from the Wessex Formation. This demonstrates that at least face of the pubis that forms the anterior margin of the obturator three large-bodied predators were present in theropod faunas of notch is preserved. Here, a low longitudinal ridge representing the Barremian of the United Kingdom. the pubic apron begins distal to the notch and extends distome- Institutional Abbreviations—BYU, Brigham Young Universi- dially from the posterior surface of the shaft. The presence of ty Museum of Geology. Provo; IWCMS, Isle of Wight County this ridge, rather than a prominent flange, suggests that the Museum Service, Sandown; MACN, Museo Argentino de obturator notch was open ventrally rather than closed off by an Ciencas Naturales “Bernadino Rivadavia”, Buenos Aires; ossified pubioischiadic membrane to form an obturator foramen. MIWG, Museum of Isle of Wight Geology, Sandown; MNA, The second specimen preserves approximately half of the con- Museum of Northern Arizona, Flagstaff; MNN, Museé National joined pubic shafts and nearly the entire distal boot (Fig. 1E–H). The shafts have a suboval cross-section that is almost as broad anteroposteriorly as it is wide mediolaterally and curve posteroventrally in lateral view. They are parallel distally but diverge *Corresponding author. proximolaterally to enclose the pelvic canal. A prominent

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FIGURE 1. Pubis (A–H) and left femur (J–O) of MIWG 6350. Proximal fragment of left pubis in A, anterior, B, posterior, C, lateral, and D, medial views. Paired pubes in E, anterior, F, left lateral, G, posterior, and H, distal views. Distal end of left femur in J–K, anterior, L, lateral, M–N, posterior, and O, distal views. In line drawings (B, C, F–H, K, N–O) hatching indicates breaks exposing internal bone surface. Abbreviations: ext, extensor groove; fen, fenestra; lco, lateral condyle; mco, medial condyle; pua, pubic apron. Scale bar equals 10 cm.

longitudinal flange, the pubic apron, extends medially from the fragments; a fragment comprising the distal condyles; and a frag- anterior margin of the medial surface of the shaft to contact the ment comprising a distal portion of the shaft proximal to the opposing flange. This contact is interrupted for approximately distal condyles (both in Fig. 1J–O). The latter two fragments half of the preserved length by a slit-like fenestra that terminates can be arranged so that they contact one another, but the con- immediately proximal to the distal expansion (Fig. 1E, G). tacting surfaces have both been slightly abraded. The anterior The conjoined distal expansion (pubic boot) is abraded ante- surface of the shaft has collapsed inwards, forming a broad, riorly, posteriorly, and distally. As preserved it is a massive angular, longitudinal furrow in the distal shaft fragment. This structure with an expanded posterior portion. However, broken collapse may have been facilitated by the thinness of the bony bone surfaces and comparisons to other theropods suggest that walls of the shaft relative to the enlarged medullary cavity the boot was originally larger, so that at least a small anterior (Fig. 1I). The anterior bone surface of the condyles is well-pre- expansion was originally present and the posterior portion was served. The medial condyle has a planar anterior surface that more expanded. Most importantly, the lateral surfaces of the slopes posterolaterally, whereas the lateral condyle has a trans- distal expansion converge posteromedially but do not meet versely convex anterior surface (Fig. 1O). The interaction of (Fig. 1H). In other theropods possessing a broad pubic boot these morphologies forms a broad extensor groove that con- (non-coelurosaurian theropods; Rauhut, 2003) the outline of the tinues proximally from the distal end of the femur. The posterior boot in distal view is triangular and the lateral surfaces meet surfaces of the condyles are strongly abraded and neither the posteriorly at a point (e.g. Galton and Jensen, 1979; Brusatte crista tibiofibularis nor the posterior part of the medial condyle et al., in press). Thus, if this was the case in MIWG 6350 then a are preserved. The outline of the condyles in distal view has substantial posterior portion is abraded. The medial line of con- been further distorted by anteroposterior crushing. tact between the left and right distal expansions has been oblit- The pubic boot has a maximum transverse width of 86 mm, erated posteriorly but is evident anteriorly. compared to 123 mm for the adult holotypic specimen of Neove- nator (MIWG 6348), and the distal end of the femur of MIWG Femur 6350 has a transverse width of 125 mm, compared to 175 mm for MIWG 6348. These measurements indicate that the linear The distal end of the left femur has been abraded and crushed dimensions of the individual represented by MIWG 6350 are anteroposteriorly. It is preserved in three fragments: a small approximately two-thirds those of MIWG 6348 resulting in an more proximal fragment that is not contiguous with the other estimated length of 5.3 meters (based on the size of Neovenator 614 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 29, NO. 2, 2009 in Brusatte et al., in press). The ontogenetic status of MIWG a slit-like fenestra between the pubic aprons is a synapomorphy 6350 is uncertain but incomplete fusion of the pubic expansions of Tetanurae rather than of a more inclusive clade. The distribu- may indicate that it had not yet reached adult size. tion of other morphologies of the fenestra between the pubes remains to be tested by phylogenetic analysis but may be of DISCUSSION value in resolving the issue of ‘ceratosaur’ monophyly (cf. Tykoski and Rowe, 2004; Allain et al., 2007) as the fenestra is Characters of both the pubis and femur indicate that MIWG altogether absent in basal saurischians such as Herrerasaurus 6350 is a basal tetanuran theropod. Two characters indicate a (PVL 2566; Novas, 1993:fig 6A). tetanuran affinity: a slit-like fenestra between the pubic aprons Comparisons with overlapping elements show that MIWG and the presence of a femoral extensor groove. The transversely 6350 differs from both Baryonyx and Neovenator, two hitherto broad morphology of the pubic boot indicates that MIWG 6350 recognized large theropods in the Wessex Formation. MIWG does not pertain to a coelurosaur. Thus the specimen can be 6350 differs from both Baryonyx and Neovenator as the pubic referred to a non-coelurosaurian tetanuran theropod (“basal shafts curve posteroventrally rather than being straight in lateral tetanuran”). Although some Late Cretaceous coelurosaurs, the view (Charig and Milner, 1997; Brusatte et al., 2008). MIWG large-bodied tyrannosaurids, possess transversely broad pubic 6350 also differs from Neovenator as it does not possess the boots (e.g. Brochu, 2002), basal tyrannosauroids such as Stoke- latter’s autapomorphic morphology of the anterior surface of sosaurus (OUMNH J.12144; Benson, 2008) have transversely the distal femur, in which the surface is almost flat and the narrow pubic boots similar to those of other coelurosaurs extensor groove is reduced to a short notch (Brusatte et al., in (Rauhut, 2003). press). Furthermore, a large suboval depression is present on the The femoral extensor groove is absent or very shallow in basal anterior surface of the medial femoral condyle of Neoveantor, theropods such as Coelophysis (Colbert, 1979), Dilophosaurus but is absent in MIWG 6350. MIWG 6350 additionally differs (Welles, 1984), and Ceratosauria (Bonaparte et al., 1990; Mad- from Baryonyx as the long axis of the medial condyle is oriented sen and Welles, 2000) and the presence of an extensor groove anteroposteriorly in distal view, rather than posteromedially, has been recovered as a synapomorphy of Tetanurae by several and the distal end of the pubis is strongly expanded, rather than cladistic analyses (e.g. Perez-Moreno et al., 1993; Holtz, 2000). weakly expanded (Charig and Milner, 1997). Another medium- Rauhut (2003) recovered a fenestra between the pubic aprons to-large-sized theropod, Eotyrannus, is also known from the as a synapomorphy of a clade subtending Dilophosaurus, Cera- Wessex Formation, as are several small theropod taxa. However, tosauria (comprising Ceratosaurus, Elaphrosaurus, and Abeli- these taxa are all coelurosaurs (Naish et al., 2001) and clearly do sauroidea), and Tetanurae. However, in Dilophosaurus (UCMP not represent the same taxon as MIWG 6350 on the basis of 37302) this fenestra is absent. Furthermore, although the fenes- small adult size and/or divergent morphology consonant with tra is present in derived ceratosaurs, such as Carnotaurus the non-coelurosaurian affinity of MIWG 6350. (MACN-CH 894), it takes a different morphology: it is located The discovery of MIWG 6350 indicates the presence of a third more distally, is suboval in section, and penetrates the pubic large-bodied basal tetanuran in the Wessex Formation. Large- boot rather than the pubic aprons (Fig. 2C). In more basal neo- bodied theropods probably filled the role of apex predators in ceratosaurs such as Ceratosaurus (BYU 12893; Fig. 2D) and Middle Jurassic–Late Cretaceous terrestrial ecosystems and the Kryptops (MNN GAD1-2; Sereno and Brusatte, 2008) the fenes- diversity of such taxa in the Wessex Formation is now one of tra is apparently absent in anterior view, but a subcircular fenes- the best understood of all Early Cretaceous dinosaur faunas. The tra that may be homologous penetrates the pubic boot diversity of large-bodied theropods in the Wessex Formation is dorsoventrally and is visible in ventral view only. A similar ven- comparable to that found in other well-known faunas in which tral fenestra is present in ‘Syntarsus’ kayentakatae (MNA basal tetanurans form a major component, such as the Upper P1.2623; Fig. 2E). Based on these observations, the presence of Jurassic Morrison Formation of the United States (the allosauroid Allosaurus, the ceratosaur Ceratosaurus, the spinosauroid Torvosaurus; Foster, 2007), the Cenomanian “continental inter- calaire” beds of Africa (the allosauroid Carcharodontosaurus, the ceratosaur Rugops, the spinosauroid Spinosaurus; Brusatte and Sereno, 2007), and the Aptian-Albian Elrhaz Formation of Africa (the allosauroid Eocarcharia, the ceratosaur Kryptops, the spinosauroid Suchomimus; Sereno and Brusatte, 2008). However, unlike these faunas, the Wessex Formation has yet to yield a ceratosaur, although the discovery of an abelisaurid would not be unexpected based on recent discoveries in similar- aged rocks in continental Europe (Carrano and Sampson, 2008). Those Late Jurassic-Early Cretaceous dinosaur faunas that are well sampled indicate the contemporaneous presence of several large-bodied theropods from a range of clades. This differs from many Late Cretaceous faunas in which only a single large preda- tor or multiple large predators of a single restricted clade are present (e.g. the tyrannosaurid faunas of North America and Asia and the abelisaurid faunas of the southern continents: Weishampel et al., 2004). The identification of MIWG 6350 as a new basal tetanuran also adds another taxon to the largely incomplete Early Creta- ceous record of Europe. Outside of the Wessex Formation, the FIGURE 2. Pubes of non-tetanuran theropods. Left pubis of Cerato- saurus (BYU 12893) in A, lateral, and D, distal views. Left pubis of only large-bodied Early Cretaceous European theropod known Carnotaurus (MACN-CH 894) in B, lateral, and C, anterior views. Paired from relatively complete and diagnostic remains is Erectopus pubes of ‘Syntarsus’ kayentakatae (MNA P1.2623) in E, distal, and F, left superbus from the Aptian-Albian of France (Sauvage, 1882; lateral views. Abbreviations: fen, fenestra; pub, pubic boot. Scale bars Allain, 2005). However, fragmentary remains ascribed to the equal 10 cm and distal views magnified Â2(D) and Â3(E). genera Becklespinax and Valdoraptor indicate the presence of SHORT COMMUNICATIONS 615 further large-bodied taxa in the English Hastings Beds Group, of Hutt, S. 2001. Catalogue of the Wealden Group Dinosauria in the Muse- somewhat older age than the Wessex Formation (Berriasian- um of Isle of Wight Geology; pp. 411–422 in D. M. Martill and Valanginian; Naish and Martill, 2007). The identification of D. Naish (eds.), Dinosaurs of the Isle of Wight. The Palaeontologi- MIWG 6350 is promising, as it testifies to the enduring potential cal Association, London. of European Lower Cretaceous units to yield new taxa even Hutt, S., D. M. Martill, and M. J. Barker. 1996. The first European allosaurid (Lower Cretaceous, Wealden Group, England). Neues after centuries of collecting. Jahrbuch fu¨ r Geologie une Palaöntologie, Monatshefte 1996:635–644. ACKNOWLEDGMENTS Hutt, S., D. M. Martill, M. J. Barker, and P. Newbery. 2001. A prelimi- We are indebted to Keith Simmonds for discovery of nary account of a new tyrannosauroid theropod from the Wessex Formation (Early Cretaceous) of southern England. Cretaceous the specimen. We thank Brooks Britt (BYU), Pat Holroyd Research 22:227–242. (UCMP), Alejandro Kramarz (MACN), Jamie Powell (PVL), Hutt, S., and P. Newbery. 2004. An exceptional vertebra from the Wes- Rod Scheetz (BYU), and especially Martin Munt (MIWG) for sex Formation (Lower Cretaceous) Isle of Wight, England. Proceed- access to specimens in their care, and Brooks Britt additionally ings of the Isle of Wight Natural History & Archaeology Society for photography (Fig. 2D). We also thank Paul Barrett, Richard 20:61–76. Butler, Dave Martill, and Sterling Nesbitt for discussion. RBJB Madsen, J. H., Jr, and S. P. Welles. 2000. 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