THE NEUROANATOMY OF MEGARAPTOR NAMUNHUAIQUII (THEROPODA: MEGARAPTORIDAE) FROM THE UPPER CRETACEOUS OF PATAGONIA, A PRELIMINARY REPORT

PAULINA CARABAJAL, A.; PORFIRI, J.

Puerto Madryn

Otro; Reunion Anual de Comunicaciones de la Asociacion Paleontologica Argentina; 2018

CENPAT

Megaraptorid neuroanatomy has been studied in a single species with known braincase: Murusraptor barrosaensis Coria and Currie from the Upper Cretaceous of Patagonia. Here, we report the brain and inner ear of a juvenile specimen (MUCPV 595) of Megaraptor namunhuaiquii Novas, which were reconstructed using a microCT scan. The preserved braincase is small (approximately 6?7cm long) and is incomplete, missing part of the skull roof, the basioccipital and all bones in front the prootics. The cranial endocast represents the hindbrain and part of the midbrain, including cranial nerves V, VII-XII and the caudal middle cerebral veins. The lack of laterosphenoids prevents to determine if the ophthalmic branch of the trigeminal nerve (V1) is separate or not. The inner ear is similar to other theropods, with an anterior semicircular canal (asc) larger than the posterior (psc), and the later larger than the lateral canal. The asc is not markedly larger than the psc (and is notposterodorsally expanded as in tyrannosaurids); they form an angle of approximately 85?90 degrees in dorsal view. The floccular process of the cerebellum is tubular and long, with its tip reaching the level of the psc. When compared to M. barrosaensis, the morphology of both, brain and inner ear are similar, showing short and ventrally convex medulla oblongata.M. namunhuaiquii however, has a markedly larger and longer floccular process. Further analysis of this data and comparisons with coelurosaur theropods will shed some light on the understanding of the phylogenetic relationships of this clade within Theropoda.