New information on the braincase and endocranial morphology of the Late Triassic neotheropod Zupaysaurus rougieri using Computed Tomography data

Abstract

Zupaysaurus rougieri is an early neotheropod from the middle Norian Los Colorados Formation of northwestern Argentina represented by an almost complete skull and several postcranial bones. Most of its braincase morphology has remained obscured by other skull bones and sediment. Additional mechanical preparation and X-ray computed tomography on the single known specimen of Zupaysaurus has allowed a detailed description of the braincase, the cranial endocast, and the inner ear of this Triassic dinosaur. Basal theropod braincases are poorly sampled and there is little information on this region, and even poorer knowledge on the brain and inner ear anatomy of Triassic forms. The virtual reconstruction of the braincase of Zupaysaurus shows anteroventrally oriented, finger-like basipterygoid processes, an elongate and horizontally projected cultriform process, and well-developed preotic pendant, basisphenoid recess, and subsellar recess. The endocranial morphology is partially reconstructed, showing an anteroposteriorly short but dorsoventrally tall cranial endocast, with well-marked demarcations between the forebrain, midbrain, and hindbrain. The inner ear preserves the three semicircular canals, but not the lagena. The posterior semicircular canal is proportionally large when compared with that of other theropods. The new information presented here on Zupaysaurus rougieri contributes to the knowledge of the neuroanatomy of basal theropods and sheds light on the evolutionary patterns of the braincase morphology in nonavian Theropoda.