early Miocene, in north Africa. Tectonic changes starting about 35 million years ago led to the formation of the Great Rift Valley, and the rise of highlands that cause rain shadows in the surrounding region. Before the rift opened, Kenya was more forested. Grasslands began to spread across Africa in the mid-Miocene, slowly replacing closed forest environments with open savannas. Any or all of these factors may have led to the replacement of Ekorus and other large mustelid hunters by modern felids, hyaenids, and canids. References Prehistoric mustelids Miocene mammals of Africa Miocene carnivorans Fossil taxa described in 2003 Prehistoric carnivoran genera Prehistoric monotypic mammal genera