New skull of Schizodelphis sulcatus Gervais, 1861 (Mammalia, Odontoceti, Eurhinodelphinidae) from the Lower Miocene of Pignan (Hérault, France) and its implications for systematics of Eurhinodelphinidae

Abstract

Schizodelphis sulcatus is the type species of the Eurhinodelphinid genus Schizodelphis and was until now only known from a rather fragmentary specimen, lacking some important parts of the skull (vertex, ear bones and apex of rostrum). The study of a well-preserved skull of S. sulcatus Gervais, discovered in the lower Miocene of Hérault (France), helps to improve the diagnosis of this enigmatic species. Diagnostic features include the low height at the base of the rostrum, the lower position of the paroccipital process compared to the height of the postglenoid process in lateral view, the ventrally deflected postglenoid process and the ovoid-shaped nasals. It also confirms that the type species of Schizodelphis is indeed distinct. For the first time in Schizodelphis, the vertex is preserved and the ear bones are found in anatomic connection with the basicranium. A cladistic analysis of cranial characters of Eurhinodelphinidae, including ear bones, is performed and reveals a close phylogenetic relationship between S. sulcatus and the North American species Schizodelphis barnesi. This analysis also highlights some apomorphies of the genus as the smoothly laterally deflected anterior spine of the bulla in ventral view and the reestablishment of the contact between the falciform process of the squamosal and the lateral lamina of the pterygoid. Conversely, the attribution of Schizodelphis morckhoviensis to the genus Schizodelphis is questioned by this analysis. © 2011 Elsevier Masson SAS.