A new fossil from the Late Miocene of Piedmont (northwestern Italy) sheds light on the evolution of the Cetotheriidae (Mammalia, Cetacea, Mysticeti)

The baleen-bearing whale Albacetus salvifactus gen. et sp. nov. from the upper Tortonian of Piedmont (north-west Italy) is described herein and compared to an extended sample of mysticete cetaceans. The new taxon belongs to the Cetotheriidae sensu stricto family-rank clade and is closely related to the genera Herentalia, Brandtocetus, Ciuciulea, Adicetus and Tranatocetus from the North Atlantic, Mediterranean and Paratethys basins. The computed tomography (CT) scan of Albacetus salvifactus revealed several previously undescribed characters including the neurovascular characters of the rostrum and the virtual skull endocast. Based on the CT scan, the periotic of A. salvifactus was threedimensionally reconstructed. The skull endocast revealed that the encephalization quotient (EQ) of A. salvifactus is in the 95% confidence interval of the EQ variation in mysticete cetaceans. Some functional areas of the brain were reconstructed based on specific impressions on the endocast surface, likely corresponding to the sylvian, ectosylvian, suprasylvian and ectolateralis fissures. Phylogenetic analysis revealed that Cetotheriidae sensu stricto is subdivided into two subclades: (1) a North Atlantic group and (2) a widespread group including Herpetocetus, Piscobalaena, Metopocetus and Cetotherium. Phylogenetic results suggest multiple invasions of the Paratethys by different cetotheriid groups. Comparative phylogenetic analyses showed that the monophyly of Caperea and Cetotheriidae sensu stricto, the monophyly of Plicogulae and the monophyly of Tranatocetidae are less parsimonious than the solution proposed herein, thereby reinforcing the monophyly of Balaenoidea, Balaenopteroidea and Thalassotherii.