When a mammalian genus is found infrequently in the fossil record, as is the case with Paranthropus, important evidence for understanding the group’s distribution and evolution can be provided by studying mammalian biogeographyBiogeography more broadly—both in localities where the group has been found, but also where it is not known. With this goal, we analyzed African fossil mammalian assemblages from ~ 3.8 to ~ 1.3 Ma, but also analyzed modern macromammal assemblages at localities where anthropogenic influences are minimized—in national parks and game reserves across the entire continent. To better mimic the restricted distribution of fossil localities, we also analyzed a subset of the modern sites using only localities in countries from which fossil hominins have been recovered. We identified three modern regions containing the largest numbers of unique mammals: West and Central Rainforests, Northern Africa, and Southern AfricaSouth(ern) Africa. For fossil assemblages, northern and southern AfricaSouth(ern) Africa similarly contain the largest numbers of unique mammals in the ~ 3.8 to ~ 1.3 Ma time period. We conclude that northern and southern Africa have been isolated for significant periods of time in the past, and that areas within eastern AfricaEastern Africa have also been isolated at various times. Some hominin species, such as those in the genus Australopithecus, likely dispersed before ~ 4.0 Ma, but during later times regions became isolated and not many mammals—other than those with specific trophic adaptationsAdaptation, such as carnivory—dispersed. Our analyses of mammalian assemblage data lead us to conclude that it is unlikely that the ancestor of Paranthropus robustus migrated into southern AfricaSouth(ern) Africa later than 4.0–3.0 Ma.