Hippopotamids from the Djurab Pliocene faunas, Chad, Central Africa

In the Djurab Desert (Chad), the fossiliferous sectors of Kossom Bougoudi, Kollé and Koro Toro have yielded a great amount of fossil hippo remains aged between ca. 5 and 3 Ma. Hippos from the first two areas represent a distinct lineage evolving in Chad during the early Pliocene. Indeed, a new species from Kollé is described ( Hexaprotodon mingoz sp. nov.) and the Kossom Bougoudi fossils may constitute its ancestral stem. At Koro Toro, a different but very rare form occurs, and its affinities remain unclear. These hippopotamids testify to a more complex family history than previously recognized, and reinforce the idea of using this group for biochronology. The hippos underscore relative endemism of the Chadian fossil faunas and would indicate a greater and earlier aridity of this region in contrast to East Africa.