Middle Pleistocene Hippopotamus amphibius (Mammalia, Hippopotamidae) from southern Europe: Implications for morphology, morphometry and biogeography

Hippopotamuses were present in Western Europe during the Pleistocene with at least two continental species: Hippopotamus antiquus and H. amphibius. The former was the large European hippopotamus, which appeared in the fossil record around 2 Ma and successfully spread across Europe before its last appearance datum (LAD) in Portugal and Greece, dated to 0.4 Ma. The extant hippopotamus, H. amphibius, first occurred in Africa around 1.5 Ma, and was well-established in Europe during the Late Pleistocene; however, its first occurrence datum (FOD) in Europe is still highly debated. Most of the H. amphibius remains collected from Middle Pleistocene localities are either badly preserved and fragmented or lacking clear stratigraphical data, in turn leading to doubtful specific attributions. A well-preservedmandible herein described, collected from Fosso Malafede (Latium, central Italy), allows to re-assess the occurrence of H. amphibius and to critically revise its earliest records. The morphological and morphometric characters of the studied remain, such as the general robustness of the studied mandible, the convex ventral profile of the mandibular corpus, the length of the teeth series, and the shape of the sagittal cross section of the mandibular symphysis, allow us to ascribe it to Hippopotamus amphibius. Fosso Malafede has been chronologically assigned to MIS 7 (∼0.25 Ma) and represents one of the best preserved H. amphibius specimen of the Middle Pleistocene of the European mainland. Accordingly, we discuss biochronological and paleobiogeographic implications, suggesting a critical revision of several remains from the Middle Pleistocene of southern Europe.