New data on the neuroanatomy of basal eusuchian crocodylomorphs (Allodaposuchidae) from the Upper Cretaceous of Spain

Abstract

The South Pyrenean Basin (northeast Spain) has yielded a rich and diverse collection of vertebrate fossil remains from the uppermost Cretaceous (upper Maastrichtian), amongst which Crocodylomorpha is one of the best represented clades. This record includes remains of the last representatives of the basal eusuchian clade Allodaposuchidae prior to its disappearance after the Cretaceous-Paleogene (K/Pg) extinction event.In this context, the holotype skulls of the allodaposuchids Arenysuchus gascabadiolorum and Agaresuchus subjuniperus were CT scanned to obtain the three-dimensional reconstruction of their inner cranial cavities, including the brain, nerves, blood vessels, paratympanic sinus system, and the paranasal sinuses. These cavities were compared with those of other crocodylomorphs, with special emphasis on other allodaposuchids and related clades such as Crocodylia. The endocranial anatomy of both taxa is consistent with their phylogenetic position as basal eusuchians, showing morphologies and neurosensorial and cognitive capabilities similar to those present in other allodaposuchids. Their inferred sensorial capabilities, such as an acute sense of olfaction and relatively good sight, fall within the range observed in most eusuchians and the crown group Crocodylia, suggesting that the sensory and cognitive skills observed in extant crocodylians were already similar at the end of the Mesozoic.Thanks to this study, all the known genera of Allodaposuchidae now have reconstructions of their inner skull cavities, making this clade one of the neuroanatomically best-studied groups among Neosuchia, providing valuable information on the neurological and neurosensorial evolution of the basal eusuchians and the early radiation of Crocodylia.