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Juvenile Megaraptor (theropod) from Cretaceous of Argentina

Ben Creisler

A new paper:

Juan D. Porfiri, Fernando E. Novas, Jorge O. Calvo, Federico L.
Agnolín, Martín D. Ezcurra & Ignacio A. Cerda (2014)
Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light
about tyrannosauroid radiation.
Cretaceous Research 51: 35–55
DOI: 10.1016/j.cretres.2014.04.007

We describe a juvenile specimen of the enigmatic Patagonian theropod Megaraptor.
We offer a detailed description of the first known skull bones of this taxon.
Skull morphology agrees with coelurosaurian affinities, bolstering the
hypothesis that megaraptorans are members of this theropod clade.
We also recognize several cranial features that are similar to
tyrannosauroid coelurosaurians.

Megaraptorids are a group of predatory dinosaurs that inhabited
Gondwana from Cenomanian to Santonian times (Late Cretaceous).
Phylogenetic relationships of megaraptorids have been matter of recent
debate, being alternatively interpreted as basal coelurosaurs,
carcharodontosaurian allosauroids, megalosauroids, and basal
tyrannosauroids. One of the main reasons for such different
interpretations is the incomplete nature of most available
megaraptorid skeletons and, in particular, the scarce information
about their cranial anatomy. Here we describe a partially preserved
skeleton of a juvenile specimen of Megaraptor namunhuaiquii that
provides substantial new information about the cranial morphology of
this Patagonian taxon. The specimen comes from the Upper Cretaceous
(Turonian–Coniacian) of the Portezuelo Formation, northwestern
Patagonia, Argentina. The anatomy of the new specimen bolsters the
recently proposed hypothesis that megaraptorids are nested within
Coelurosauria, and possibly within Tyrannosauroidea. The most relevant
features that megaraptorans share with tyrannosauroids include several
foramina on the premaxillary body, extremely long and straight
prenarial process of the premaxilla, incisiviform premaxillary teeth
with a D-shaped cross-section, and cranially expanded supratemporal
fossae separated from each other by a sharp sagittal median crest on
frontals, which was presumably extended caudally above the parietals
(not preserved). Information gathered from the present specimen allows
to make for the first time a reconstruction of the skull of Megaraptor
and hypothesize about evolutionary trends within Tyrannosauroidea.