Hoofed Mammals Intro
Hooves are enlarged toes and nails. Horses and donkeys are odd-toed ungulates; they walk on an enlarged middle toe adapted for running. Gazelles, camels, goats, and sheep are even-toed ungulates; they have split-hooves and walk on their third and forth toes, adapted for movement on rough terrain. The remaining toes are vestigial.
Hoofed animals emerged around 55 million years ago, 10 million years after the dinosaurs died out. The ancestors of horses were once very numerous and successful, but the spread of grasses around 30 million years ago favored even-toed ungulates with multi-chambered stomachs, better-suited to digest grass cellulose. This is reflected in the greater diversity of even-toed ungulates in Jordan today.