Braincase and Neuroanatomy of Pseudochampsa ischigualastensis and Tropidosuchus romeri (Archosauriformes, Proterochampsia)

Abstract

Proterochampsids form a clade of archosauriforms endemic to South America, interpreted as the sister-taxon of the crown-group Archosauria. Because of this, aspects of the skull osteology in this group are particularly important to understand the evolutionary radiation of Archosauriformes. The braincase anatomy of archosauriforms was described for several groups, including few proterochampsids. However, paleoneurological studies on basal archosauriforms are scarce, and these were never conducted on proterochampsids, except for few preliminary analyses of Tropidosuchus romeri and Pseudochampsa ischigualastensis. Here we add descriptive information on the braincase and partial endocranial morphology of the type-specimens of the proterochampsids Pseudochampsa ischigualastensis and Tropidosuchus romeri based on CT scans. Reptile Encephalization Quotient (REQ) and olfactory ratios were calculated for the first the time for a proterochampsid, indicating a high olfactory acuity for Tropidosuchus romeri, and suggesting a lifestyle similar to that of living crocodilians. The neurocranial information presented here is important due the scarcity of such data for Proterochampsidae.