A southern tyrant reptile.

Tyrannosaurids monopolized the apex predator niche in latest Cretaceous Laurasia. Unfortunately, the preceding 100-million-year tyrannosauroid lineage is poorly documented, and its fossil record is restricted to the northern continents. We report an Australian tyrannosauroid, represented by a pubis from the late Early Cretaceous of Victoria. This demonstrates that these extraordinarily successful predators were not restricted to Laurasia. The advanced morphology and small size of the specimen shows that tyrannosauroids with the characteristic short arms and robust skulls probably had a global distribution in the Early Cretaceous. Thus, a potentially cosmopolitan grade of small tyrannosauroids with a tyrannosaurid-like body plan preceded the Late Cretaceous rise of the colossal tyrannosaurids.

A large Cretaceous theropod from Patagonia, Argentina, and the evolution of carcharodontosaurids.

The Cretaceous Carcharodontosauridae is the latest clade of carnosaurs, including the largest predatory dinosaurs yet recorded. Albeit spectacular for their size, the skeletal anatomy of these theropods remains poorly-known, and their diversity was until recently restricted to two Cenomanian species: the highly derived Giganotosaurus carolinii, from southern South America, and the incompletely known Carcharodontosaurus saharicus, from northern Africa. Here we describe an older and basal member of the group, Tyrannotitan chubutensis gen. et sp. nov., from Aptian strata of Patagonia, Argentina. The new taxon gives new insights into the systematics and evolution of carcharodontosaurids and offers a better understanding of the evolution of Southern theropod faunas. We suggest that carcharodontosaurids radiated in Gondwana sharing with spinosaurids the role of top-predators until their extinction in Cenomanian-Turonian times. During this interval, the diplodocoid sauropods and giant titanosaurians went extinct (probably as part of a global-scale crisis), and the smaller abelisaurid theropods took dominance, reigning until the end of the Cretaceous. Electronic Supplementary Material is available.