Osteology of the Late Jurassic Portuguese Sauropod Dinosaur Lusotitan Atalaiensis (Macronaria) and the Evolutionary History of Basal Titanosauriforms
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bs_bs_banner Zoological Journal of the Linnean Society, 2013, 168, 98–206. With 30 figures Osteology of the Late Jurassic Portuguese sauropod dinosaur Lusotitan atalaiensis (Macronaria) and the evolutionary history of basal titanosauriforms PHILIP D. MANNION1,2*, PAUL UPCHURCH3, ROSIE N. BARNES3 and OCTÁVIO MATEUS4,5 1Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ, UK 2Museum für Naturkunde, Invalidenstrasse 43, 10115 Berlin, Germany 3Department of Earth Sciences, UCL, University College London, Gower Street, London WC1E 6BT, UK 4Department of Earth Sciences (CICEGE-FCT), Universidade Nova da Lisboa, 2829-516 Monte de Caparica, Portugal 5Museu da Lourinhã, Rua João Luís de Moura, 2530-157 Lourinhã, Portugal Received 20 July 2012; revised 24 January 2013; accepted for publication 12 February 2013 Titanosauriforms represent a diverse and globally distributed clade of neosauropod dinosaurs, but their inter- relationships remain poorly understood. Here we redescribe Lusotitan atalaiensis from the Late Jurassic Lourinhã Formation of Portugal, a taxon previously referred to Brachiosaurus. The lectotype includes cervical, dorsal, and caudal vertebrae, and elements from the forelimb, hindlimb, and pelvic girdle. Lusotitan is a valid taxon and can be diagnosed by six autapomorphies, including the presence of elongate postzygapophyses that project well beyond the posterior margin of the neural arch in anterior-to-middle caudal vertebrae. A new phylogenetic analysis, focused on elucidating the evolutionary relationships of basal titanosauriforms, is presented, comprising 63 taxa scored for 279 characters. Many of these characters are heavily revised or novel to our study, and a number of ingroup taxa have never previously been incorporated into a phylogenetic analysis. We treated quantitative characters as discrete and continuous data in two parallel analyses, and explored the effect of implied weighting. Although we recovered monophyletic brachiosaurid and somphospondylan sister clades within Titanosauriformes, their compositions were affected by alternative treatments of quantitative data and, especially, by the weighting of such data. This suggests that the treatment of quantitative data is important and the wrong decisions might lead to incorrect tree topologies. In particular, the diversity of Titanosauria was greatly increased by the use of implied weights. Our results support the generic separation of the contemporaneous taxa Brachiosaurus, Giraf- fatitan, and Lusotitan, with the latter recovered as either a brachiosaurid or the sister taxon to Titanosauriformes. Although Janenschia was recovered as a basal macronarian, outside Titanosauria, the sympatric Australodocus provides body fossil evidence for the pre-Cretaceous origin of titanosaurs. We recovered evidence for a sauropod with close affinities to the Chinese taxon Mamenchisaurus in the Late Jurassic Tendaguru beds of Africa, and present new information demonstrating the wider distribution of caudal pneumaticity within Titanosauria. The earliest known titanosauriform body fossils are from the late Oxfordian (Late Jurassic), although trackway evidence indicates a Middle Jurassic origin. Diversity increased throughout the Late Jurassic, and titanosauri- forms did not undergo a severe extinction across the Jurassic/Cretaceous boundary, in contrast to diplodocids and non-neosauropods. Titanosauriform diversity increased in the Barremian and Aptian–Albian as a result of radiations of derived somphospondylans and lithostrotians, respectively, but there was a severe drop (up to 40%) in species numbers at, or near, the Albian/Cenomanian boundary, representing a faunal turnover whereby basal titanosauriforms were replaced by derived titanosaurs, although this transition occurred in a spatiotemporally staggered fashion. © 2013 The Linnean Society of London, Zoological Journal of the Linnean Society, 2013, 168, 98–206. doi: 10.1111/zoj.12029 *Corresponding author. E-mail: [email protected] Re-use of this article is permitted in accordance with the Terms and Conditions set out at http://wileyonlinelibrary.com/ onlineopen#OnlineOpen_Terms 98 © 2013 The Linnean Society of London, Zoological Journal of the Linnean Society, 2013, 168, 98–206 LUSOTITAN AND TITANOSAURIFORM EVOLUTION 99 ADDITIONAL KEYWORDS: biogeography – continuous data – Cretaceous – Gondwana – implied weighting – Laurasia – Lourinhã – Mamenchisauridae – Mesozoic – phylogeny – pneumaticity – Titanosauria. INTRODUCTION Curry Rogers, 2005; Wilson, 2005a; Mannion & Calvo, 2011; Mannion et al., 2011b; Mannion & Otero, 2012), The Late Jurassic terrestrial fauna of Portugal com- a global distribution (McIntosh, 1990; Upchurch prises a diverse dinosaur assemblage (Lapparent & et al., 2004a; Cerda et al., 2012a), and a temporal Zbyszewski, 1957; Antunes & Mateus, 2003; Mateus, range extending from the Middle Jurassic through to 2006). Sauropods are represented by at least four the end-Cretaceous (Day et al., 2002, 2004; Upchurch taxa: a diplodocid (Dinheirosaurus lourinhanensis; & Martin, 2003; Upchurch et al., 2004a). However, Bonaparte & Mateus, 1999; Mannion et al., 2012), a the inter-relationships of titanosauriforms are poorly probable basal eusauropod (Lourinhasaurus alenque- understood, with little resolution or consensus (e.g. rensis; Lapparent & Zbyszewski, 1957; Dantas et al., Salgado et al., 1997; Sanz et al., 1999; Smith et al., 1998; Upchurch, Barrett & Dodson, 2004a), a turia- 2001; Wilson, 2002; Upchurch et al., 2004a; Curry saur (Mateus, 2009; Ortega et al., 2010; Mocho, Rogers, 2005; Calvo et al., 2007; Canudo, Royo-Torres Ortega & Royo-Torres, 2012; Mateus, Mannion & & Cuenca-Bescós, 2008; González Riga, Previtera Upchurch, in review), and Lusotitan atalaiensis. The & Pirrone, 2009; Hocknull et al., 2009; Ksepka & latter was originally considered a new species of Bra- Norell, 2010; Carballido et al., 2011a, b; Gallina chiosaurus (Lapparent & Zbyszewski, 1957) before & Apesteguía, 2011; Mannion, 2011; Mannion & being assigned to its own genus within Titanosauri- Upchurch, 2011; Santucci & Arruda-Campos, 2011; formes (Antunes & Mateus, 2003; Upchurch et al., Zaher et al., 2011; Royo-Torres, Alcalá & Cobos, 2012). 2004a), although it has never been fully described. Furthermore, most titanosauriform analyses have Brachiosaurus altithorax is known from the Late focused on titanosaurs, with only a small sample of Jurassic Morrison Formation of North America putative basal titanosauriforms included. The excep- (Riggs, 1903) and a second species, Brachiosaurus tion to this is a recent analysis by D’Emic (2012) that brancai, was described from the contemporaneous concentrated on basal forms: 25 ingroup taxa were Tendaguru Formation of Tanzania (Janensch, 1914). included, representing approximately 50% of putative A recent revision demonstrated numerous anatomical basal members of Titanosauriformes (see below). differences between these two titanosauriform species In this paper, we provide a detailed redescription and argued for their generic separation, proposing and new diagnosis of the Portuguese sauropod Luso- the new binomial Giraffatitan brancai for the African titan atalaiensis. This work represents part of a series taxon (Taylor, 2009). Chure et al. (2010; see also of papers in which we will revise the Late Jurassic Whitlock, 2011a) questioned this separation based on Portuguese sauropod fauna (see also Mannion et al., the sister-taxon relationship of the two species recov- 2012). We also present a new phylogenetic analysis, ered in Taylor’s (2009) phylogenetic analysis (see also consisting of revised and novel characters, focused on Royo-Torres, 2009). Following Taylor (2009), Ksepka elucidating the evolutionary relationships of basal & Norell (2010), Carballido et al. (2012), and D’Emic titanosauriforms. (2012, 2013) included Brachiosaurus and Giraffatitan as separate operational taxonomic units (OTUs). Ksepka & Norell (2010) recovered them in a polytomy with three North American Cretaceous taxa, INSTITUTIONAL ABBREVIATIONS Carballido et al. (2012) placed them in a polytomy CAMSM, Sedgwick Museum, University of Cam- with Somphospondyli, whereas Giraffatitan was bridge, UK; CM, Carnegie Museum of Natural recovered in a basal position to Brachiosaurus in the History, Pittsburgh, PA, USA; CPT, Museo de la Fun- analysis of D’Emic (2012, 2013). However, none of dación Conjunto Paleontológico de Teruel-Dinópolis, these analyses included Lusotitan; thus, we currently Aragón, Spain; DMNH, Denver Museum of Natural do not know how the Portuguese form is related to History, Denver, CO, USA; FMNH, Field Museum of these two taxa, or to other basal titanosauriforms. Natural History, Chicago, IL, USA; HMN, Humboldt Titanosauriformes represents the most diverse Museum für Naturkunde, Berlin, Germany; IVPP, clade of sauropod dinosaurs, with over 90 distinct Institute of Vertebrate Paleontology and Paleoanthro- species (Salgado, Coria & Calvo, 1997; Wilson & pology, Beijing, China; MACN, Museo Argentino de Upchurch, 2003, 2009; Upchurch et al., 2004a, 2011a; Ciencias Naturales ‘Bernardino Rivadavia’, Buenos © 2013 The Linnean Society of London, Zoological Journal of the Linnean Society, 2013, 168, 98–206 100 P. D. MANNION ET AL. Aires, Argentina; MAPA, Museo Aragones de Paleon- centrum, one posterior dorsal neural spine, 21 caudal tología, Aragón, Spain; MCF, Museo ‘Carmen Funes’, vertebrae, thoracic rib fragments, one sacral rib, 12 Neuquén, Argentina;