The Cretaceous beds of Patagonia have yielded the most comprehensive record of Cretaceous theropods from Gondwana and includes at least five main theropod lineages: Abelisauroidea, Carcharodontosauridae, Megaraptora, Alvarezsauridae, and Unenlagiidae. The best represented theropod clades in the Late Cretaceous terrestrial strata of the Neuquén Basin are the Abelisauroidea and the Carcharodontosauridae. Most discoveries come from continental units of ages ranging from Barremian to Maastrichtian. The lowest levels of the Cretaceous are well exposed in the marine and terrestrial deposits of the Mulichinco and Bajada Colorada formations.
The Carcharodontosauridae includes the largest land predators in the early and middle Cretaceous of Gondwana, like the popular Giganotosaurus carolinii, and in some way, they were considered as ecological equivalents to the Laurasian tyrannosauroids. The group evolved large skulls surpassing the length of the largest skull of Tyrannosaurus rex; and some derivaded forms had heavily sculptured facial bones. Another common trait is the fusion of cranial bones. Lajasvenator ascheriae, a new specimen from the Valanginian Mulichinco Formation, represents the oldest Cretaceous carcharodontosaurid from South America. The name derived from the Lajas, the city near where the specimen was found; and venator, a Latin word for hunter. The specific name honors Susana Ascheri, owner of the land where the fossil was discovered.
The holotype (MLL-PV-005) of this medium-sized theropod is an incomplete but partially articulated skeleton that includes a partial skull, partially articulated presacral vertebral series, four articulated caudal vertebra and fragments of the pelvic girdle. A second specimen (MLL-PV-Pv-007) includes the anterior ends of both dentaries, a quadratojugal, and fragments of cervical vertebrae, ribs and a possible tarsal bone. The holotype of Lajasvenator was collected in 2010 during fieldwork at Pilmatué. The second specimen was recovered in 2012.
Lajasvenator exhibits anterior projections on cervical prezygapophyses, lip-like crests on the lateral surfaces of cervical postzygapophyses, and bilobed anterior processes on cervical ribs. The phylogenetic analysis indicates that Lajasvenator is clearly nested in a basal position within Carcharodontosauridae.
Coria, R.A., Currie, Currie, P.J., Ortega, F., Baiano, M.A., An Early Cretaceous, medium-sized carcharodontosaurid theropod (Dinosauria, Saurischia) from the Mulichinco Formation (upper Valanginian), Neuquén Province, Patagonia, Argentina, Cretaceous Research (2019) https://doi.org/10.1016/j.cretres.2019.104319
Novas, F.E., et al., Evolution of the carnivorous dinosaurs during the Cretaceous: The evidence from Patagonia, Cretaceous Research (2013), http://dx.doi.org/10.1016/j.cretres.2013.04.001