New analysis resolves long-standing confusion over the age of a key fossil. Modern hippos first appeared in Europe during the Middle Pleistocene, a geological era ranging from about 770,000 to 126,000 years ago. This is the result of a study published in the open access journal "PLOSONE" on November 22, 2023 by Beniamino Mecozzi of Sapienza University of Rome and colleagues.
Hippopotamus skull from Cava-Montanari. Dorsal (A), ventral (B), right (C), left (D) and posterior (E) views of the skull. Mandibular occlusal view (F), right lateral view (G), and left lateral view (H). Scale bar 10 cm. Image source: Mecozzi et al., 2023, PLOSONE, CC-BY4.0
The modern hippopotamus (Hippopotamusamphibius) originated from African ancestors during the Quaternary period, when hippopotamuses were very common in Europe. However, the details of the origins and spread of modern hippos into Europe are unclear and highly controversial. In this study, Mecozzi and colleagues provided new insights by analyzing fossil hippopotamus skulls from the TordiQuinto study area in Rome.
The TordiQuinto skull, currently housed in the University Museum of Earth Sciences of Sapienza University in Rome, is one of the most complete hippopotamus specimens known from the European Pleistocene, but its significance has been unclear due to uncertainty about its age and the location of its original excavation.
After the skull was repaired in 2021, researchers analyzed the composition of the sediments in the skull cavity. The results showed that they were consistent with the local Valle Guilia formation, indicating that the geological age of the skull was between 560,000 and 460,000 years. Skull and tooth morphology also confirm that the skull is a modern species, Hippopotamus amphibian.
Historical image of the Tordi Quinto area and the same area today, obtained from the archives of the Istituto Superiore Perla Protezione e Ricerca Ambientale (ISPRA, A,B). Image source: Mecozzi et al., 2023, PLOSONE, CC-BY4.0
The study found the skull to be the oldest known fossil of a modern hippopotamus in Europe. These findings shed light on the history of hippos in Europe, strengthen the hypothesis of hippopotamus dispersal in the early mid-Pleistocene, and broaden understanding of the deep history of these large mammals. Hippopotamuses are highly influential species in modern and ancient ecosystems and are important indicators of past climate and environmental conditions.
The authors add: "The restoration of exposed mammalian bones from the Terra Museum of Earth Sciences at the University of Sapienza in Rome has provided new data on ancient fossils. A multidisciplinary study of skulls from Cava Montanari (Rome) redefines the first dispersal of amphibious hippopotamuses across Europe".