Osteology of the Late Jurassic Portuguese sauropod dinosaur Lusotitan atalaiensis (Macronaria) and the evolutionary history of basal titanosauriforms

摘要: 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 Lourinha Formation Portugal, taxon previously referred to Brachiosaurus. The lectotype includes cervical, dorsal, caudal vertebrae, elements forelimb, hindlimb, pelvic girdle. is valid can be diagnosed by six autapomorphies, including presence elongate postzygapophyses that project well beyond posterior margin neural arch in anterior-to-middle vertebrae. A new phylogenetic analysis, focused on elucidating evolutionary relationships basal titanosauriforms, presented, comprising 63 taxa scored for 279 characters. Many these characters are heavily revised or novel our study, number ingroup have never been incorporated into analysis. We treated quantitative as discrete continuous data two parallel analyses, explored effect implied weighting. Although recovered monophyletic brachiosaurid somphospondylan sister clades within Titanosauriformes, compositions were affected alternative treatments and, especially, weighting such data. This suggests treatment important wrong decisions might lead incorrect tree topologies. In particular, diversity Titanosauria was greatly increased use weights. Our results support generic separation contemporaneous Brachiosaurus, Giraffatitan, Lusotitan, with latter either Titanosauriformes. Janenschia macronarian, outside Titanosauria, sympatric Australodocus provides body fossil evidence pre-Cretaceous origin titanosaurs. sauropod close affinities Chinese Mamenchisaurus Tendaguru beds Africa, present information demonstrating wider distribution pneumaticity Titanosauria. earliest known titanosauriform fossils late Oxfordian (Late Jurassic), although trackway indicates Middle origin. Diversity throughout Jurassic, titanosauriforms did not undergo severe extinction across Jurassic/Cretaceous boundary, contrast diplodocids non-neosauropods. Titanosauriform Barremian Aptian–Albian result radiations derived somphospondylans lithostrotians, respectively, there drop (up 40%) species numbers at, near, Albian/Cenomanian representing faunal turnover whereby replaced titanosaurs, this transition occurred spatiotemporally staggered fashion. © 2013 Linnean Society London