Megaraptorans as members of an unexpected evolutionary radiation of tyrant-reptiles in Gondwana

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

Buenos Aires

Jornada; XXVI Jornadas Argentinas de Paleontologia de Vertebrados; 2012

Megaraptor and its close relatives were poorly known carnivorous dinosaurs that inhabited South America, Australia, Asia, and possiblyAfrica, during Early to Late Cretaceous times. These theropods became relevant in the last years with the discovery of morecomplete skeletons. Recent phylogenetic analyses have viewed Megaraptor and its close relatives within a monophyletic group namedas Neovenatoridae. This clade includes Megaraptor, Aerosteon, Orkoraptor, Chilantaisaurus, Fukuiraptor, Neovenator, and Australovenator.Neovenatorids were considered members of Allosauroidea, and particularly as the sister group of Carcharodontosauridae, asa clade of allosauroids that survived up to the end of the Cretaceous. However, we found anatomical information that supports thatneovenatorids are a non-monophyletic group, and that Megaraptor and related genera are deeply nested within Coelurosauria andclosely related to the Asiamerican Tyrannosauridae. Among coelurosaurian synapomorphies, these theropods share elongate metacarpals,ilium with enlarged fossa cuppedicus, distal end of tibia with a flat facet for the reception of the ascending process of the astragalusand gracile fibula and metatarsals. The Asian genus Fukuiraptor is recovered as the basalmost form of this new coelurosaurianclade. The phylogeny proposed here indicates that Neovenator is remotely related to Megaraptor and its kin, and indicates that thistaxon is more closely related to Carcharodontosauridae, rather than with Coelurosauria. Chilantaisaurus from the Early Cretaceousof China is considered as an uncertain Coelurosauria. The newly recovered theropod clade considerably improves our knowledgeabout the scarcely documented basal radiation of coelurosaurs, filling a 15 MY gap in tyrannosauroid evolution.