Diets of hartebeest (Alcelaphus buselaphus) and roan antelope (Hippotragus equinus) were assessed at the Nazinga Game Ranch in southern Burkina Faso, West Africa. Microhistological analysis of feces indicated that dietary overlap was high during the rainy (X̄ = 73.7%) and cool-dry (68.2%) seasons, low during the hot-dry season (48.2%), and lowest during the last month of the hot-dry season (31.5%). As the hot-dry season progressed and food presumably became less available, diets of the two antelopes diverged. Hartebeest maintained a high percentage of grass in their diet, but roan antelope switched from being predominantly grazers (>95% grass) to mixed feeders (<50% grass). As grass feeders, both antelopes have skeletal features that facilitate acquisition and grinding of highly fibrous diets, but 11 of 12 mass-relative indices of the skull morphology of hartebeest exceeded those of roan antelope. Because of those differences in skull morphology, and in keeping with the “long-faced” hypothesis, hartebeest were apparently more capable than roan antelope of acquiring and masticating scarce regrowth of perennial grasses when availability of forage was lowest. Such divergence within a single foraging class of African bovids, such as grass feeders, should reduce competition and perpetuate coexistence.