BRAINCASE AND NEUROANATOMY OF BAJADASAURUS PRONUSPINAX (SAUROPODA, DICRAEOSAURIDAE) FROM THE CRETACEOUS OF PATAGONIA

GARDERES, J.P.; GALLINA, P.A.; PAULINA CARABAJAL, A.; WHITLOCK, J.

Salta

Jornada; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2022

Universidad Nacional de Salta

Since the arrival of clinical imaging in paleontology, paleoneurology became a flourishing scope for investigations, especially in dinosaurs. Sauropods have been one of the most studied groups, and Dicraeosauridae was not an exception. Cranial remains and/or endocasts are preserved for several Jurassic and Cretaceous dicraeosaurids (Amargasaurus, Dicraeosaurus, Suuwassea and the indeterminate dicraeosaurid MLL 003), allowing the study of neuroanatomy of a sizable proportion of the clade. These taxa share a set of characteristic traits, such as an extremely large longitudinal dorsal venous sinus, a large transverse sinus, and a floccular process. Here, we present novel information on the braincase of the holotype of Bajadasaurus and its associated endocast, based on CT scans. Although incompletely preserved, the braincase presents openings for the olfactory tract and most cranial nerves and vascular foramina. There is a single foramen for CN II, CN VI enters the expanded hypophyseal fossa, and there is a single foramen for CN XII. The braincase presents an expanded pneumatic cavity caudal to the hypophyseal fossa, which probably opens caudally between the basal tubera. The cranial endocast has laterally expanded and well-defined cerebral hemispheres, an expanded longitudinal dorsal venous sinus contacting the nasal capsules separately from the olfactory tract, which also conspicuously expands caudodorsally (conforming a dural expansion with a pyramidal outline), a clearly defined dorsoventral transverse sinus, and a well-defined medullar region, with a dorsal rostrocaudal constriction, and a ventral keel. A floccular recess is difficult to recognize due to the incomplete preservation of the otic capsulae. Although preliminarilyanalyzed, a) the longitudinal dorsal venous sinus contacting the nasal capsules separatedfrom the olfactory tract; b) a ventral keel on the floor the medulla oblongata; and c) a dorsally expanded dural expansion (beyond the expansion seen in other dicraeosaurids),make up a tentatively exclusive combination of traits of Bajadasaurus.