A new species of Hippopotamidae, Hexaprotodon dulu nov. sp., was discovered in the Middle Awash valley, Afar, Ethiopia. It was found in the Sagantole Formation, within volcaniclastic beds aged between 5.2 Ma and 4.9 Ma (40Ar/39Ar). It is therefore the oldest hippo species described as yet from Ethiopia. This hexaprotodont hippo exhibits a general morphology that is primitive, close in that respect to other Mio-Pliocene forms. However, its cranium and dentition display a distinctive association of measurements and features. This new species increases the hippo fossil record in East Africa. It also reinforces the hypothesis of hippo endemism in each African basin as early as the basal Pliocene.

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