A large tusk of Metaxytherium (Dugongidae, Sirenia, Mammalia) from the Late Miocene of Montebamboli (southern Tuscany, Italy): evolutionary and paleoecological implications

An isolated large tusk, belonging to the historical finds of the Collezione di Geologia “Museo Giovanni Capellini” (Bologna, Italy) and originally identified as belonging to a hippopotamus, is here described and reassigned to the genus Metaxytherium (Dugongidae, Sirenia, Mammalia). According to the museum label, this specimen originates from the now-exhausted lignite deposits of Montebamboli (Tuscany, central Italy); the latter are late Tortonian to early Messinian in age and were deposited in a lacustrine environment. The Montebamboli tusk displays strong similarities with an elderly Metaxytherium subapenninum specimen from the Pliocene deposits of Bra (Piedmont, northern Italy) as well as with an isolated Metaxytherium tusk, now apparently lost, from Miocene deposits of Son Morelló (Mallorca, Spain). The Late Miocene occurrence of a large-tusked Metaxytherium in the Mediterranean Basin calls into question the anagenetic trend previously proposed for the Euro-North African species of Metaxytherium , thus also stimulating further research on the intra- and interspecific tusk size variability within this lineage. Furthermore, this specimen represents the first record of a marine species from the lignites of Montebamboli, indicating the proximity of marine settings.