A review on the Pleistocene occurrences and palaeobiology of Hippopotamus antiquus based on the record from the Barranc de la Boella Section (Francolí Basin, NE Iberia)

Abstract

The study of European Pleistocene Hippopotamus presents unresolved questions and a lack of consensus among specialists being matter of hotly debate in the last decades. The number of taxa, their geographical and chronological distribution and their palaeobiological affinities are still under evaluation. The present work presents the results of comparative analyses using descriptive anatomy, linear biometry and geometric morphometrics of Hippopotamus specimens found in the archaeopalaeontological outcrops of the Barranc de la Boella Section (Francolí Basin, NE Iberian Peninsula) and other coeval European sites in the context of the record of the genus Hippopotamus in Europe and its putative migrations from Africa. The deposits from Barranc de la Boella Section documented for the first time the presence of hominids with Acheulian technology and hippos roughly coinciding with the Early-Middle Pleistocene Transition (EMPT), one of the periods with strongest climate asymmetry throughout the Pleistocene. The evaluation of the studied specimens and the other European record favor the consideration of Hippopotamus antiquus as the only taxon of its family present in Europe from the Early Pleistocene (ca. 2.1 Ma) to the mid-Middle Pleistocene (ca. 0.4 Ma), when the extant species (Hippopotamus amphibius) dispersed from Africa. Even so, there is a need for a more detailed understanding of the large intraspecific variability and sexual dimorphism reported within the genus Hippopotamus to characterise the phenotype of individuals in its populations across different chronologies, geographic locations, and environmental conditions. The detailed review of the distribution of H. antiquus during the EMPT raises the possibility that the Iberian and Italic peninsulas acted as climatic refugia for its populations strongly dependents of the aquatic environment during the coldest climatic stages (e.g. MIS 22).