Middle Pleistocene Hippopotamuses from the Italian Peninsula: an Overview

Our work presents an updated overview of the Italian Middle Pleistocene records of hippopotamuses, including the two species Hippopotamus antiquus and Hippopotamus amphibius. In addition to reviewing several well-known fossils in the literature, a large number of samples are described herein for the first time. Following the recent results published in the literature, where the skull from the Middle Pleistocene of Cava Montanari (ca. MIS 13) was confirmed to belong to H. amphibius, one of the aims of this work was to investigate the H. antiquus–H. amphibius transition. A morphological analysis applied to a large sample confirmed the validity of the arrangement of the enamel ridges of the external surfaces of the lower canines as a diagnostic character for specific identifications. Finally, biometric analyses allowed us to test the size variability during the Middle Pleistocene, which confirmed that H. antiquus was generally larger than H. amphibius. Nevertheless, the remains of H. antiquus dated to ca. 600 ka show a reduced size when compared to older fossils of the same taxon, probably as a response to severe glacial conditions that occurred during MIS 16.