Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation

PORFIRI, J.; NOVAS, F. E.; CALVO, J. O.; AGNOLIN, F. L.; EZCURRA, M. D.; CERDA, I. A.

CRETACEOUS RESEARCH (PRINT)

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2014 vol. 51

0195-6671

Megaraptorids are a group of predatory dinosaurs that inhabited Gondwana from Cenomanian to Santoniantimes (Late Cretaceous). Phylogenetic relationships of megaraptorids have been matter of recentdebate, being alternatively interpreted as basal coelurosaurs, carcharodontosaurian allosauroids, megalosauroids,and basal tyrannosauroids. One of the main reasons for such different interpretations is theincomplete nature of most available megaraptorid skeletons and, in particular, the scarce informationabout their cranial anatomy. Here we describe a partially preserved skeleton of a juvenile specimen ofMegaraptor namunhuaiquii that provides substantial new information about the cranial morphology ofthis Patagonian taxon. The specimen comes from the Upper Cretaceous (TuronianeConiacian) of thePortezuelo Formation, northwestern Patagonia, Argentina. The anatomy of the new specimen bolstersthe recently proposed hypothesis that megaraptorids are nested within Coelurosauria, and possiblywithin Tyrannosauroidea. The most relevant features that megaraptorans share with tyrannosauroidsinclude several foramina on the premaxillary body, extremely long and straight prenarial process of thepremaxilla, incisiviform premaxillary teeth with a D-shaped cross-section, and cranially expandedsupratemporal fossae separated from each other by a sharp sagittal median crest on frontals, which waspresumably extended caudally above the parietals (not preserved). Information gathered from thepresent specimen allows to make for the first time a reconstruction of the skull of Megaraptor and hypothesizeabout evolutionary trends within Tyrannosauroidea.