Ungulates, or hoofed mammals, are the most diverse group of mammals living today. With few exceptions they are herbivores. The first cat-sized ungulates appear in fossil record near the end of the Mesozoic Era, but they bore little resemblance to modern hoofed mammals.
After the extinction of large Mesozoic reptiles 65 million years ago, ungulates and other mammals began to diversify into the myriad forms we know today. This marked the beginning of the Cenozoic Era—The Age of Mammals.