NEUROANATOMY OF THE TITANOSAUR SAUROPOD NARAMBUENATITAN PALOMOI FROM THE UPPER CRETACEOUS OF PATAGONIA, ARGENTINA

Abstract

Narambuenatitan palomoi is a titanosaurian sauropod from the Upper Cretaceous of North Patagonia. Considered initially as a basal titanosaur, this taxon has uncertain phylogenetic relationships within the clade. An X-ray Computed Tomography (CT) scan of the holotype braincase allowed the first reconstruction of the brain and inner ear of this taxon, making it possible to compare the neuroanatomy with that of closely related forms. Except for the slightly sigmodal shape of the endocast in lateral view—considered a basal condition—, the brain shows derived titanosaurian traits such as a poorly developed dorsal expansion and a single exit for Cranial Nerve (CN) XII. In contrast, the inner ear exhibits slender and long semicircular canals (the anterior semicircular canal is distinctly longer than the posterior semicircular canal), which is a character present in more basal representatives of the group, such as Sarmientosaurus. We consider, however, the morphology of the inner ear as an unreliable indicator of phylogenetic position. Furthermore, there is a remarkable similarity between the morphology of the endocast of Narambuenatitan and the possible saltasaurid from (FAM 03.064), from the Upper Cretaceous of Fox-Amphoux-Métisson, France, suggesting saltasaurine affinities for the Argentinean taxon.

Keywords

• Paleoneurology
• Cranial endocast
• Inner ear
• Dinosauria