The linkage between faunal change and climate change really has to do with a very basic observation, which is that organisms are fundamentally linked to the resource availability of a given landscape. As the energetics of the landscape, the utility of the landscape changes, the fauna have a series of options that that they can either adapt or become extinct.
Those grasslands didn’t come into being until almost two million years ago. Actually, the first appearance of that really open dry, arid, vegetation coincided in time almost exactly with this Acheulian tool kit, this very sophisticated bi-facial rock blade.
The lesson that we take home from the study of how climate change may have changed early human evolution is a recognition of the larger truth, which is actually echoed throughout the geologic record of the co-evolution of life on the planet and climate change — is that there are many, many examples of extinctions linked to events of massive environmental change.