Skull anatomy of the bizarre crocodylian Mourasuchus nativus (Alligatoridae, Caimaninae)

BONA, P.; DEGRANGE, F.J.; FERNANDEZ, M.S.

The Anatomical Record

John Wiley & Sons, Inc.

Año: 2013 p. 227 - 239

1932-8494

Mourasuchus is a Miocene Alligatoridae endemic of South America, represented by four species. Together with the giant Purussaurus, Mourasuchus is the most peculiar crocodylian taxon of South American neogene Caimaninae and even one of the most bizarre forms between eusuchians crocodiles. The phylogenetic relationships between Mourasuchus species have never been explored and detailed skull descriptions are scarce. The main goal of this study is to provide new skull morphological data and cranial recesses of M. nativus, including a new tomography analysis (3D modeling). We observed that several diagnostic characters of Purussaurus such as nasal and lacrymal bones not in contact, nasal and frontal separated by prefrontals and posterior dorsal margin of the skull table strongly concave, are shared with Mourasuchus. M. nativus is characterized by the presence of solid transversal squamosal bumps, large postemporal fenestrae and a quadrate latero-caudal bridge separating V2-V3 trigeminal openings. Comparing with other crocodiles, the endocast of M. nativus is more sigmoidal shaped in lateral view; the canal of the supraorbital ramus of V2 is more vertically orientated, with a thick tympanic branch canal opening in a large foramen aligned with trigeminal foramen and the canal of the X tympanic ramus is also very thick. Contrary to extant alligatorids, the medial pharyngeal recess remains pair in all its extension and only connects its symmetrical tube near the external ventral opening. The knowledge of the internal skull anatomy of Mourasuchus contributes to the understanding of the general morphology of alligatorids Caimaninae and its variation.