CONICET | Buscador de Institutos y Recursos Humanos

Here, we present the first paleoneurological study based on CT scans of the skull of a new riojasaurid sauropodomorph (PVSJ 849) from the Los Colorados Formation (Late Triassic) of Argentina. The CT scan allowed the rendering of the braincase and endocranial cavities, resulting in the most complete anatomical data for a South American representative of the clade. The cranial endocast of PVSJ 849 characterizes by a low dorsal expansion, cerebral hemispheres poorly expanded laterally, elongated olfactory tract and bulbs, a relatively well developed flocculus of the cerebellum, and bulbous and short pituitary. The cranial endocast has a marked sigmoidal shape in lateral view, with the olfactory bulbs aligned with the forebrain, the midbrain posteroventrally inclined and the hindbrain parallel and ventral to the forebrain. The flocculus is similar in size to that in the basal form Saturnalia tupiniquim and basal Neotheropoda, but contrasting with the small flocculus in the sauropodomorph Plateosaurus sp (a state of character that is considered a derived condition within Sauropodomorpha). The inner ear has slendersemicircular canals, and the relative size of anterior, posterior and lateral semicircular canals are similar to S. tupiniquim. In dorsal view, the angle formed between anterior and posterior semicircular canals is about 80 degrees. The brain, cranial nerves and inner ear of few Triassic sauropodomorph dinosaurs have been studied, and within South American taxa these include only S. tupiniquim from Brazil. The preliminary comparisons of the neuroanatomy suggest a primitive condition within Riojasauridae, represented by PVSJ 849 with a neuroanatomy that is more similar to S. tupiniquim than to the more derived (and more closely related) Plateosaurus sp.