How did Africa's grasslands get started?

Between 10 million and 6 million years ago, vegetation across much of the world underwent a transformation, as warmth-adapted grasses displaced previously dominant plants, shrubs and trees. The new grasses carried out the chemical reactions required for photosynthesis in a distinct new way. Scientists have labeled this new process the C4 pathway. In East Africa, the changeover coincided with the evolution of mammal lineages that we recognize today, including early human ancestors. Today, C4 plants comprise about one-quarter of the Earth's vegetation, from the Great Plains of North America to western China, Australia and much of sub-Saharan Africa.

source https://www.lifetechnology.com/blogs/life-technology-news-blog/how-did-africas-grasslands-get-started