Endocranial anatomy of plesiosaurians (Reptilia, Plesiosauria) from the Late Cretaceous (Turonian) of Goulmima (southern Morocco)

ABSTRACT

Despite recent advances in noninvasive imaging, Plesiosauria remains one of the least explored clades of reptiles with respect to paleoneuroanatomy. Only partial endocasts, obtained from either latex casts or imprints left on the braincase, have been described. In this contribution, the digital endocasts of three plesiosaurian specimens were analyzed: two referred to the elasmosaurid Libonectes morgani and one to Polycotylidae indet., all from the Late Cretaceous (Turonian) of Goulmima (Morocco). They were computed tomography (CT)-scanned to provide new anatomical information on the plesiosaurian endocast, endosseous labyrinth, and cranial nerves. Results show that the three endocasts are very similar to each other. They appear anteroposteriorly elongated and horizontally oriented in lateral view, with long olfactory tracts, relatively small and incomplete olfactory bulbs, a reduced pineal organ, distinguishable optic lobes, and a possible large cerebellum constituting the main component in size of the endocast. The endocranial features reconstructed here are compared with those of other plesiosaurians, as well as other marine reptiles, notably to discuss their intraspecific and interspecific variability. This study provides pioneer data in order to estimate the impact of both phylogenetic and ecological constraints on the endocranial morphology of plesiosaurians and proposes a few preliminary paleobiological suggestions.

ACKNOWLEDGMENTS

This work was supported by a grant from the Agence Nationale de la Recherche under the LabEx ANR-10-LABX-0003-BCDiv, in the program ‘Investissements d’avenir’ ANR-11-IDEX-0004-02. We are grateful to the Staatliches Museum für Naturkunde Stuttgart for the loan of SMNS 81783 and to E. Maxwell for access to the collection of the Stuttgart museum. We are grateful to the Rhinopolis Museum for the loan of D1-8213. We thank the AST-RX platform at the MNHN for access to the CT scanner and M. Garcia-Sanz (MNHN, UMS 2700 OMSI) for producing the CT scans. We are also grateful to the 3D platform (UMR 7207, CR2P, MNHN) for giving access to the 3D imaging facilities. Finally, we thank editor R. F. O’Keefe, reviewer J. M. Neenan, and an anonymous referee for helpful comments and suggestions.