A new study conducted by researchers from the University of Utah questions the long-held belief that mammal evolution in Africa, including that of modern human ancestors, was primarily driven by the expansion of grasslands. According to this research, changes in vegetation may have influenced the spatial range of mammal groups, leading to extinctions and the origin of new species.

The study focused on modeling the responses of 58 modern herbivore species to changes in shrub cover in parks and nature reserves in Africa. The results revealed a preference for environments with approximately half of shrub cover, while very few species preferred open grasslands or closed forests.

The research team also took into account the dietary preferences of mammal species, including grazers, browsers, frugivores, and mixed feeders. Species preferring open habitats showed a decrease in probability as shrub cover increased, while species preferring closed forests showed a decrease in probability with a shift towards open grasslands. The study found that some species, such as impalas, buffalos, and wildebeests, did not show sensitivity to changes in vegetative cover.

The researchers concluded that the most likely ecosystem to have proliferated in the late Cenozoic was a savanna environment, dominated by interspersed grasslands with shrubs and trees. These environments were highly influenced by annual precipitation, which could reduce growth productivity in drier conditions or dilute plant nutrients in areas with excessive rainfall.

The study also emphasized the limitations of using fossil remains to reconstruct past landscape changes. Previous studies have suggested that certain fossils indicate dense shrublands, but this research demonstrates that these fossils may not accurately represent tree cover in a larger area. The researchers caution against relying solely on fossils as “indicator species” during paleoecological reconstructions.

In summary, the study suggests that the expansion of grasslands through the late Cenozoic may not have been the primary driver of mammal speciation and extinction in Africa. Instead, changes in vegetative cover, influenced by factors such as precipitation, played a significant role in the evolution of mammals on the continent.

– Kathryn G. Sokolowski et al, Do grazers equal grasslands? Strengthening paleoenvironmental inferences through analysis of current African mammals, Palaeogeography, Palaeoclimatology, Palaeoecology (2023). DOI: 10.1016/j.palaeo.2023.111786