Neuroanatomy of Gryposuchus neogaeus (Crocodylia, Gavialoidea): a first integral description of the braincase and endocranial morphological variation in extinct and extant gavialoids

BONA, PAULA; PAULINA CARABAJAL, ARIANA; GASPARINI, ZULMA

EARTH AND ENVIRONMENTAL SCIENCE TRANSACTIONS OF THE ROYAL SOCIETY OF EDINBURGH

ROYAL SOC EDINBURGH

Lugar: Edinburgo; Año: 2016

1755-6910

Morphological studies of the braincase and cranial endocast of fossil crocodylians,especially gavialids, are scarce. Here, we present a detailed description of the neuroanatomy ofGryposuchus neogaeus from the Miocene of Argentina, based on CT scans. The cranial endocast issub-horizontal and the angle formed between the mid-brain and the hind-brain is poorly marked.When compared with Gavialis gangeticus, the mid-brain of G. neogaeus is relatively shorter,although the distribution of cranial nerves is similar. In the floor of the endocranial cavity, posteriorto the dorsum sellae, there is a median foramen that leads into a canal that runs anteroventrallythrough the basisphenoid to penetrate the posterior wall of the pituitary fossa (open foramen forthe basilar artery?). The same structure is present in G. gangeticus, but is absent in other livingcrocodylians, suggesting a potential synapomorphy of Gavialoidea. The pneumaticity of the skullroof and the lateral branches of the pharyngotympanic system in G. neogaeus are markedly reducedwhen compared with the extant species. Comparisons with the living Gavialis indicate that thepattern of braincase morphology of Gavialidae was present in the Miocene; however, the internalmorphology, including brain shape, pneumaticity of the skull roof and basicranium, is different inthe two species. This work is the first step to understand the variation of the neuroanatomy in thisgroup of archosaurs and its palaeobiological implication.