Archaeopotamus is an extinct genus of Hippopotamidae that lived between 7.5 and 2.58 million years ago in Africa and the Middle East. The genus was described in 2005 to encompass species of hippos that were previously grouped in Hexaprotodon.
Archaeopotamus means "the ancient of the river". Of all identified hippos, only Kenyapotamus is older. Kenyapotamus, however, is only known from partial fossils; Archaeopotamus is the oldest well-identified hippo.[1]
Many prehistoric hippo fossils are known primarily through fossils of the lower jaw. Archaeopotamus, like Hexaprotodon, has three pairs of incisors. Unlike other Hexaprotodon, Archaeopotamus has a highly elongate mandibular symphysis. The informal name "narrow muzzled hippos" has been suggested for this genus.
A. lothagamensis is a species whose fossils were discovered at Lothagam, a site southwest of Lake Turkana in Kenya and first described in 2000. When first described, the species was classified as Hexaprotodon lothagamensis, although the significant morphological differences between other Hexaprotodon species, were noted.[2]
A. lothagamensis was smaller than the modern hippopotamus and also smaller than A. harvardi and with a more slender skeleton. It was, however, significantly larger than the modern pygmy hippopotamus.
A. harvardi is a species of hippo first described in 1977, originally as Hexaprotodon harvardi.[3] Although the proportions of A. harvardi and A. lothagamensis are similar, the former species is significantly smaller. Femurs of A. harvardi are approximately the same size as those of the modern hippopotamus.