Evolution of the carnivorous dinosaurs during the Cretaceous: the evidence from Patagonia

NOVAS, FERNANDO EMILIO; AGNOLÍN, FEDERICO LISANDRO; EZCURRA, MARTÍN; PORFIRI, JUAN DOMINGO; CANALE, JUAN IGNACIO

CRETACEOUS RESEARCH (PRINT)

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2013

0195-6671

Patagonia yielded the most comprehensive fossil record of Cretaceous theropods from Gondwana, consisting of 31 nominal species belonging to singleton taxa and six families: Abelisauridae, Noasauridae, Carcharodontosauridae, Megaraptoridae nov. fam., Alvarezsauridae and Unenlagiidae. They offer relevant anatomical information that allows a better interpretation of theropods discovered in other regions of Gondwana. Abelisauroids are the best represented theropods in Patagonia and undewent an evolutionary radiation documented from Early Cretaceous through latest Cretaceous ages, being represented by the clades Abelisauridae and Noasauridae. Patagonian carcharodontosaurids are known from three taxa (Tyrannotitan, Giganotosaurus and Mapusaurus), as well as from isolated teeth, ranging from Aptian through Cenomanian beds. These allosauroids constituted the top pretadors during mid-Cretaceous times, in congruence with the presence of gigantic titanosaur sauropods. Megaraptorans became relevant in the last years with the discovery of more complete remains. Megaraptor, Aerosteon and Orkoraptor have been documented in Cretaceous beds from Argentina, and they exhibit close relationships with the Aptian genera Australovenator, from Australia, and Fukuiraptor, from Japan. The Gondwanan megaraptorans are gathered into the new family Megaraptoridae, and the Asiatic Fukuiraptor is recovered as its immediate sister taxon of this clade. Although megaraptorans have been recently interpreted as members of Allosauroidea, we present evidence that they are deeply nested within Coelurosauria. Moreover, anatomical information supports Megaraptora as more closely related to the Asiamerican Tyrannosauridae than thought. Megaraptorans improve our knowledge about the scarsely documented basal radiation of Gondwanan coelurosaurs and tyrannosauroids as a whole. Information at hand indicates that South America was a cradle for the evolutionary radiation for different coelurosaurian lineages, including some basal forms (e.g., Bicentenaria, Aniksosaurus), megaraptorans, alvarezsaurids less derived than the Laurasian ones, and unenlagiids, revealing that Gondwanan coelurosaurs played sharply different ecological roles, and that they were taxonomically as diverse as in the northern continents. The unenlagiids represent an endemic South American clade that have been recently found as more closely related to birds than to dromaeosaurid theropods. Analysis of theropod fossil record from Gondwana shows the highest peak of origination index occurred during the Aptian-Albian and a less intense one in the Campanian time spans. Besides, peaks of extinction index are recognized for the Cenomanian and Turonian-Coniacian time spans. In comparisson, the Laurasian pattern differs from that of Gondwana in the presence of an older extinction event during the Aptian- Albian time-span and a high origination rate during the Cenomanian time-bin. However, both Laurasian and Gondwanan theropod records coincide in a peak of origination rates during the Campanian.