Since the extinction of the dinosaurs, hoofed mammals have been the planet's dominant herbivores. Native to all continents except Australia and Antarctica, they include not only even-toed artiodactyls (pigs, hippos, camels, deer, antelopes, giraffes, sheep, goats, and cattle) and odd-toed perissodactyls (horses and rhinos), but also tethytheres (elephants and their aquatic relatives, manatees and seas cows) and cetaceans (whales and dolphins),...