Major worldwide division of the Tertiary Period that began about 36.6 million years ago and ended about 23.7 million years ago. It follows the Eocene Epoch and precedes the Miocene Epoch. The term Oligocene is derived from Greek and means the epoch of few recent forms referring to the sparseness of the number of modern animals that originated during the Oligocene. Many large mountain systems and herbivorous mammals began to develop, however. During this epoch, many of the older types of mammals became extinct and the first apes appeared. The largest land mammal of all time, Baluchitherium, is known from Asia, and the first mastodons are known from Egypt. In North America, primitive horses were evolving, including three-toed forms such as Mesohippus and Miohippus. Pigs and peccaries first appeared in the early Oligocene of Europe and reached North America late in the epoch. The earliest apelike form, Parapithecus, is known from Oligocene deposits in Egypt, which also have yielded remains of several kinds of Old World monkeys. The earliest New World monkeys are known from late Oligocene deposits in South America.