Neuroanatomy of a diplodocid sauropod dinosaur from the Lower Cretaceous of Patagonia, Argentina

Abstract

Diplodocid neuroanatomy is known from four Late Jurassic forms from North America and Africa. Recently, a partial braincase of a diplodocid sauropod (MMCh-Pv- 232), tentatively assigned to Leinkupal laticauda Gallina et al., 2014, preserving a complete basicranium, right laterosphenoid, prootic, parietal, otooccipital and right half of the supraoccipital, was recovered from Bajada Colorada Formation (Berriasian–Valanginian). Reconstructions of the braincase, cranial endocast and inner ear were performed via X-ray Computed Tomography and segmentation. The endocast is represented by the pituitary body (inclined at 69° from the base of the medulla oblongata –similar to Diplodocus), the caudal-most region of the cerebral hemispheres and the internal carotid arteries, the midbrain, showing Cranial Nerve (CN) III and CN IV exiting the braincase through a single opening; and the hindbrain, with CN V exiting the braincase through a single opening as in other sauropods, the ventral CN VI entering the pituitary fossa caudally, CN IX-XI exiting the braincase through a single opening (metotic foramen), and CN XII exiting the braincase through two canals. The inner ear preserved a caudoventrally inclined conical lagena, a sub-rectangular fenestra ovalis, the ampulla of the Anterior Semicircular Canal, the crus commune, and a Lateral Semicircular Canal. The length of the lagena suggests a lower auditive capacity in comparison to other sauropods. The morphological similarities of the braincase and endocast to other diplodocids reinforce the tentative assignation of MMCh-Pv-232 to Leinkupal, and expands the knowledge in neuroanatomy of South American sauropods.