Abundant remains of a small bovid have been unearthed at the basal Middle Miocene locality of Arrisdrift, Orange River Valley, Namibia. Among the more than 10,000 vertebrate fossils excavated at the site only two horn cores have been found. The bovid from Arrisdrift is one of the oldest known species with horn cores. It is here classified as Namacerus gariepensis nov. gen. nov. sp. Namacerus differs from Eotragus artenensis by its smaller size, greater hypsodonty, and other morphological characters of the dentition. From a phylogenetic point of view the Arrisdrift bovid may well belong to the stem group from which the rest of the bovid lineages were derived. The hypothesis of an African origin for the family Bovidae is strongly supported by the new data. During the Early and basal Middle Miocene Africa possessed a diversity of bovid genera and it was the scene of a major radiation within the family, as indicated by the presence of diverse cranial morphotypes which are primitive with respect to those known from Eurasia.