During the Jurassic (201-145 mya) the breakup of the supercontinent Pangaea continued and accelerated with the opening of the North Atlantic by the rifting of Africa and North America, giving rise to the supercontinents of Laurasia and Gondwana. The sea level rise flooded continental areas around Pangaea, forming huge epicontinental seas, especially in northern Africa and eastern Laurasia (modern China). The world was predominantly warm with at least four times the present level of atmospheric CO2. The period is also characterized by the explosive adaptive radiation of dinosaurs.
By the Mid-Jurassic, Gondwana, the southern margen of supercontinent Pangea started to break up in different blocks: Antarctica, Madagascar, India, and Australia in the east, and Africa and South America in the west. During this period, the Tetanurae reached a global distribution. Tetanuran theropods comprise the majority of Mesozoic predatory dinosaurs, including Allosaurus and Tyrannosaurus, and the lineage leading to extant birds. Unfortunatelly, the fragmentary nature of the earliest known members of this group difficults our understanding of their early radiation. Asfaltovenator vialidadi gen. et sp. nov., a new basal tetanuran from the Middle Jurassic of Argentina, shed new ligth on the early radiation of this group. The generic name refers from Cañadón Asfalto Formation, the site where the fossil was found, and venator, a Greek word for hunter. The specific name honors the Administración de Vialidad Provincial of Chubut and the Dirección Nacional de Vialidad, for their aid to the Museo Paleontológico Egidio Feruglio.
Discovered in 2002 by Leandro Canesa, the holotype (MPEF PV 3440) includes an almost complete skull and a partial skeleton. The skull is high and slightly arched, similar to that of other allosauroids and reached 75–80 cm long. The estimated body length of the holotype is 7–8 m, which makes Asfaltovenator comparable in size to the well-known Allosaurus.
Asfaltovenator shows an unusual mosaic of tetanuran characters. Megalosauroid characters include a pronounced kink in the anterodorsal margin of the maxillary ascending process, a medially closed maxillary fenestra, a deep posterior groove on ventral process of postorbital, and a broad fossa below the occipital condyle. Allosauroid characters include the presence of a pronounced supranarial fossa, the nasal participation in the antorbital fossa, presence of pneumatic foramina in the nasal, and lateral nasal crests.
Tetanurae has been tradionally divided in three major clades: Megalosauroidea, Coelurosauria, and Allosauroidea. The phylogenetic analysis of A. vialidadi suggest that Allosauroidea and Megalosauroidea have a common ancestor that they do not share with coelurosaurs. The new study also suggest that the Pliensbachian-Toarcian extinction event was a potential driver of tetanuran radiation.
Rauhut, Oliver W. M.; Pol, Diego (2019), Probable basal allosauroid from the early Middle Jurassic Cañadón Asfalto Formation of Argentina highlights phylogenetic uncertainty in tetanuran theropod dinosaurs https://www.nature.com/articles/s41598-019-53672-7
Carrano, M. T., Benson, R. B. J., & Sampson, S. D. (2012). The phylogeny of Tetanurae (Dinosauria: Theropoda). Journal of Systematic Palaeontology, 10(2), 211–300. doi:10.1080/14772019.2011.630927