Neurocranial anatomy of Paralligator (Neosuchia: Paralligatoridae) from the Upper Cretaceous of Mongolia

Abstract

Neurocranial features appear to be phylogenetically informative and key in assessing the still contentious relationships within Crocodylomorpha. However, the braincases of many non-crocodylian taxa are incompletely studied precluding the assessment of evolutionary modifications at the base of Crocodylia. Here, we describe the braincase osteology and neuroanatomy of the paralligatorid crocodylomorph Paralligator from the Upper Cretaceous of Mongolia based on computed tomography (CT)-scanning, segmentation, and 3D modelling of several specimens. The anatomy of the brain endocast, nerves, and the paratympanic pneumatic cavities of Paralligator is consistent with its phylogenetic position close to or at the base of Eusuchia. Paralligator shares a suit of neuroanatomical features with basal eusuchians and crocodylians reflecting the plesiomorphic condition for Crocodylia. In addition, differences in the brain endocasts between the larger-sized individuals of Paralligator and Kansajsuchus and the smaller Shamosuchus are consistent with ontogenetic changes in extant crocodylians. This suggests that members of the more basal clade Paralligatoridae and the crown-group Crocodylia share similar brain modifications during ontogeny. We also review the distribution of the mesethmoid in Crocodylomorpha and show its presence in several clades including Paralligatoridae and Dyrosauridae.