Berberosaurus

Abstract: We describe the new basal abelisauroid dinosaur Austrocheirus isasii gen. et sp. nov. from the Late Cretaceous Pari Aike Formation of southwestern Patagonia, Argentina. The preserved remains include manual bones, a distal tibia, and some pedal and axial elements. Austrocheirus is differentiated from other basal theropods by the presence of metacarpal III with a dorsoventrally compressed shaft and posteriorly displaced collateral tendon fossae located at the same level of the proximal end of distal condyles, and pedal phalanges with a conspicuous longitudinal crest delimitating the dorsal margin of the distal collateral tendon fossae. A cladistic analysis recovered the new species as more derived than Ceratosaurus and Berberosaurus, but within a polytomy at the base of Abelisauroidea, an assignment supported by two abelisauroid synapomorphies: distal end of tibia with a planar vertical scar for the reception of the ascending process of the astragalus that occupies most of its anterior surface and is medially bounded by the longitudinally oriented facet; and scar for the reception of the ascending process with a median vertical ridge, which imbeds into a crescentic vertical groove on the posterior surface of the ascending process of the astragalus forming an interlocking tibiotarsal articulation. Furthermore, Austrocheirus represents the first known medium-sized Late Cretaceous abelisauroid bearing nonatrophied hands. The evidence provided here suggests that the strong reduction of the forelimb recorded in derived abelisaurids is not directly correlated with their increased body-size, but it seems to be an evolutionary event exclusive to this lineage within Ceratosauria.

Abstract: The homology of the tridactyl hand of birds is a still debated subject, with both paleontological and developmental evidence used in support of alternative identity patterns in the avian fingers. With its simplified phalangeal morphology, the Late Jurassic ceratosaurian Limusaurus has been argued to support a II-III-IV digital identity in birds and a complex pattern of homeotic transformations in three-fingered (tetanuran) theropods. We report a new large-bodied theropod, Saltriovenator zanellai gen. et sp. nov., based on a partial skeleton from the marine Saltrio Formation (Sinemurian, lowermost Jurassic) of Lombardy (Northern Italy). Taphonomical analyses show bone bioerosion by marine invertebrates (first record for dinosaurian remains) and suggest a complex history for the carcass before being deposited on a well-oxygenated and well-illuminated sea bottom. Saltriovenator shows a mosaic of features seen in four-fingered theropods and in basal tetanurans. Phylogenetic analysis supports sister taxon relationships between the new Italian theropod and the younger Early Jurassic Berberosaurus from Morocco, in a lineage which is the basalmost of Ceratosauria. Compared to the atrophied hand of later members of Ceratosauria, Saltriovenator demonstrates that a fully functional hand, well-adapted for struggling and grasping, was primitively present in ceratosaurians. Ancestral state reconstruction along the avian stem supports 2-3-4-1-X and 2-3-4-0-X as the manual phalangeal formulae at the roots of Ceratosauria and Tetanurae, confirming the I-II-III pattern in the homology of the avian fingers. Accordingly, the peculiar hand of Limusaurus represents a derived condition restricted to late-diverging ceratosaurians and cannot help in elucidating the origin of the three-fingered condition of tetanurans. The evolution of the tridactyl hand of birds is explained by step-wise lateral simplification among non-tetanuran theropod dinosaurs, followed by a single primary axis shift from digit position 4 to 3 at the root of Tetanurae once the fourth finger was completely lost, which allowed independent losses of the vestigial fourth metacarpal among allosaurians, tyrannosauroids, and maniraptoromorphs. With an estimated body length of 7.5 m, Saltriovenator is the largest and most robust theropod from the Early Jurassic, pre-dating the occurrence in theropods of a body mass approaching 1,000 Kg by over 25 My. The radiation of larger and relatively stockier averostran theropods earlier than previously known may represent one of the factors that ignited the trend toward gigantism in Early Jurassic sauropods.

Abstract: Here we describe the forearm and manus of the ceratosaurian theropod dinosaur Ceratosaurus nasicornis Marsh, 1884, from the Upper Jurassic Morrison Formation of the western U.S.A. Recently removed from exhibition and reprepared, the holotype offers important new information on the morphology of this taxon that bears on the evolution of the forelimb in nonavian theropod dinosaurs more generally. The ulna and radius show particular similarities to those of Dilophosaurus and Eoabelisaurus but lack features that characterize derived abelisaurids. In the manus, Ceratosaurus bears short first phalanges, like more derived taxa in the clade, but retains metacarpals that are much more similar to those of Dilophosaurus, Berberosaurus, and Eoabelisaurus. Taken together, and incorporated with existing phylogenetic data on other ceratosaurs, these data are consistent with the placement of Ceratosaurus as close to Abelisauroidea but basal to Eoabelisaurus. More importantly, they strongly imply that the extremel...

Abstract: The complete osteology of the basal sauropod Tazoudasaurus naimi from the late Early Jurassic Toundoute continental series of Ouarzazate Province, Morocco, is presented. The described material belongs to juvenile to adult individuals. The skeleton of Tazoudasaurus is virtually complete except for the skull and presents a combination ofplesiomorphic and apomorphic sauropodomorph characters. Phylogenetic analysis indicates that Tazoudasaurus shares with Vulcanodon several derived features that include strongly transversely flattened tibial shaft and the marked dorsoventral flattening of the unguals of pedal digits II and III. Both taxa are placed within the Vulcanodontidae, at the base of a new clade named Gravisauria n. nom. Our analysis underscores the major morphological changes that occur among Gravisauria between the Vulcanodontidae and the Eusauropoda. The numerous remains of Tazoudasaurus were recovered from a bone-bed associated with a few remains of the basal abelisauroid Berberosaurus. A minimum of six individuals was buried at the site. Taphonomical data suggest that Tazoudasaurus had a gregarious behaviour. The different interpretations of the evolution of the configuration and posture of the manus in basal sauropods can be tested thanks to the discovery of a complete articulated manus of Tazoudasaurus. The latter is clearly digitigrade with a spreading configuration of the metacarpus. Early sauropod evolution is analyzed in a broad extinction/ radiation perspective. Prosauropoda and Coelophysoidea extinction around the Pliensbachian-Toarcian boundary, followed by the late Early Jurassic to Middle Jurassic radiation ofGravisauria, Neoceratosauria, Tetanurae and Euornithopoda are linked to the Pliensbachian-Toarcian mass extinction event.