Grasslands and grazers
The expansion of grasslands gave rise to a new mode of feeding among herbivores grazing. The even-toed ungulates (hoofed mammals), especially ruminants, were better suited to eating the coarse, poorly nutritious grasses than the odd-toed ungulates because of their more highly developed stomachs. Ruminants have four-chambered stomachs containing microbes that digest cellulose.