The occurrence of freshwater turtle remains in the late Miocene lignites of southern Tuscany (Montebamboli and Casteani, Italy) has been known since the nineteenth century. Three chelonian species were recognized by Ristori in 1891: Emys depressa, E. campanii, and E. parva. Revision of their type material, together with the study of new fossils from a different but correlated locality, Pian Calcinaio (Scansano), allows one to state that they can be referred to the genus Mauremys and that they belong to one single species. The new combination M. campanii (Ristori, 1891) is here proposed. Phylogenetic analysis indicates that M. campanii is closely related to the modern post-Miocene group of Mauremys species and shows a sister-group relationship with the Plio-Pleistocene M. gaudryi. The remains of M. campanii come from an insular setting which progressively lost its endemic mammal fauna, defined as the Oreopithecus Zone Fauna, enabling us to compare the pattern of survival of the chelonians with that of the mammals. In contrast to the radical turnover suffered by mammals, softshell turtles (Trionyx sp.) and terrapins (M. campanii) are present both in the pre-Messinian V1–V2 and Messinian V3 assemblages. Terrestrial tortoises (Testudo amiatae Pantanelli, 1893, Testudo s.l.) show a different pattern, because they appear only in the V3 assemblage, possibly because they apparently dispersed into Italy as recently as the Messinian. M. campanii represents the southernmost evidence of the genus Mauremys in the uppermost Miocene of Europe, filling a gap in the palaeogeographic and chronological distribution of this genus.