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

NOVAS, F. E.; AGNOLIN, F. L.; EZCURRA, M. D.; PORFIRI, J.; CANALE, J. I.

CRETACEOUS RESEARCH (PRINT)

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2013 vol. 45

0195-6671

Patagonia has 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 provideanatomical information that allows improved interpretation of theropods discovered in other regions ofGondwana. Abelisauroids are the best represented theropods in Patagonia. They underwent an evolutionaryradiationdocumented fromthe Early Cretaceous through to the latest Cretaceous, and are represented by theclades Abelisauridae and Noasauridae. Patagonian carcharodontosaurids are known from three taxa (Tyrannotitan,Giganotosaurus and Mapusaurus), as well as from isolated teeth, collected from Aptian to Cenomanianbeds. These allosauroids constituted the top predators during the mid-Cretaceous, during whichgigantic titanosaur sauropodswere the largest herbivores. Megaraptorans have become better documentedin recent years with the discovery of more complete remains. Megaraptor, Aerosteon and Orkoraptor havebeen described from Cretaceous beds from Argentina, and these taxa exhibit close relationships with theAptian genera Australovenator, from Australia, and Fukuiraptor, from Japan. The Gondwanan megaraptoransare gathered into the newfamily Megaraptoridae, and the Asiatic Fukuiraptor is recovered as the immediatesister 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, anatomicalinformation supports Megaraptora as more closely related to the Asiamerican Tyrannosauridae thanthought. Megaraptorans improve our knowledge about the scarcely documented basal radiation of Gondwanancoelurosaurs and tyrannosauroids as awhole. Information at handindicates that South Americawas acradle for the evolutionary radiation for different coelurosaurian lineages, including some basal forms (e.g.,Bicentenaria, Aniksosaurus), megaraptorans, alvarezsaurids less derived than those of Laurasia, and unenlagiids,revealing that Gondwanan coelurosaurs played sharply differing ecological roles, and that theyweretaxonomically as diverse as in the northern continents. The unenlagiids represent an endemic SouthAmerican clade that has been recently found to be more closely related to birds than to dromaeosauridtheropods. Analysis of the theropod fossil record from Gondwana shows the highest peak of originationindex occurred during the AptianeAlbian and a less intense one in the Campanian time spans. Additionally,peaks of extinction index are recognized for the Cenomanian and TuronianeConiacian time spans. Incomparison, the Laurasian pattern differs fromthat of Gondwana in the presence of an older extinction eventduring the AptianeAlbian time-span and a high origination rate during the Cenomanian time-bin. BothLaurasian and Gondwanan theropod records show a peak of origination rates during the Campanian.