It has long been appreciated that mammal dentitions reveal information about diet. A study of African Neogene herbivore dentitions indicates that mammals with grazing adaptations have existed in Africa from the Early Miocene to the Present, suggesting the availability of grass in the environments throughout the period. However, there have been dramatic changes in the mammal communities possessing grazing adaptations. Initially, during the early Miocene the majority of mammals showing such dental adaptations were small, including rodents, macroscelidids and lagomorphs. By Late Miocene times, many medium to large mammals show grazing adaptations, and by the Plio-Pleistocene such adaptations reached a maximum development. These changes are considered to correlate closely with the inferred biomass of grass in the environment, being minimal in Early Miocene forested environments, and maximal in the Plio-Pleistocene steppic grasslands. Detailed examination of the southwest African and eastern African fossil records reveals that grasslands developed considerably earlier in southern Africa than in the equatorial regions. A result of this was that southern African faunas contain a greater diversity of grazing mammals at earlier periods than those in the equatorial zone. Indeed, a number of mammalian lineages adapted to grazing appear to have originated in the south and then spread northwards as environmental conditions opened up there. A number of southern lineages occupied the new equatorial grassland niches before local lineages could adapt to the new conditions. Such local lineages either went extinct or their ranges diminished, a few managing to survive in the central and west African forests.