The Late Miocene hippopotamid, Archaeopotamus pantanellii nov. comb., from the Casino Basin (Tuscany, Italy): paleobiogeographic implications

Fossil remains from the latest Messinian of Casino Basin (Tuscany, Italy) are known since the beginning of the nineteenth century. Among the others, the mammal assemblage includes Mesopithecus pentelicus, Tapirus arvernensis, Propotamochoerus provincialis and scarce and poorly preserved remains of a hippopotamid, consisting of a mandibular symphysis fragment, an apical fragment of a lower canine, some isolated lower incisors, a fragmented second upper premolar and a second lower molar. These specimens were initially referred as Hippopotamus hipponensis and later ascribed to the new species Hippopotamus pantanellii (recently reported as Hexaprotodon? pantanellii). However, this attribution has been disputed during the past years. The hippopotamid remains from the Casino Basin are revised here in order to clarify their systematic position and to infer paleobiogeographic and evolutionary patterns within the Mediterranean fossil record of Hippopotamidae. The morphology of the remains collected from the Casino Basin more closely resembles the African than the Asian hippopotamids' lineage and therefore the Tuscan remains should be more properly referred as Archaeopotamus pantanellii. The latter species probably dispersed into Tuscany from the Iberian Peninsula where the presence of Archaeopotamus crusafonti is well documented.