New finds of Metaxytherium serresii (Gervais, 1847) (Mammalia: Sirenia) from the Upper Miocene of Monte Poro (Calabria, Italy)

We summarize the osteology, update phylogenetic characters and document variability and biometrics of the species Metaxytherium serresii Gervais, 1847 (Sirenia, Dugongidae, Halitheriinae), by providing new diagnostic cranial and postcranial remains from the Miocene of Monte Poro (Vibo Valentia, Calabria, Italy). The new data confirm the marked polymorphism within the genus Metaxytherium, which was already noted. The characters and measurements of the new specimens confirm the reduction in the body size that the species underwent, probably as an ecophenotypic adaptation to changes preceding the Messinian Salinity Crisis of the Mediterranean. The new fossil material, while not differing significantly from the finds already known, demonstrates a broader range of intraspecific morphological variability of the species M. serresii.