PLIOCENE EPOCH

major worldwide division of the Tertiary Period extending from about 5.3 to 1.6 million years ago. It is often divided into the Early Pliocene Epoch (5.3 to 3.4 million years ago) and the Late Pliocene Epoch (3.4 to 1.6 million years ago). The Pliocene is the last and shortest epoch of the Tertiary Period. It follows the Miocene Epoch of the Tertiary Period and precedes the Pleistocene Epoch of the Quaternary Period. The Pliocene is also subdivided into two ages and their corresponding rock stagesnamely, the Zanclean and the Piacenzian. Pliocene deposits are known throughout the world. Early Pliocene deposits are well known from the Mediterranean region, the Siwalik Hills of India, and the Honan and Shansi provinces of China. Pliocene environments were generally cooler and drier than those of preceding Tertiary epochs, as revealed by the remains of plants and trees. A very modern aspect is seen in the vertebrate faunas of the Northern Hemisphere. Older groups of animals became extinct throughout the preceding Miocene Epoch. Although similarities are evident between the faunas of Eurasia and North America, little faunal interchange appears to have occurred between the two regions. The similarities are probably due to the continuation of forms that migrated between the two areas late in the Miocene. It is likely that during the early Pliocene a remarkably homogeneous fauna existed from Spain and Africa to China. Mastodons (elephant-like animals) underwent a great evolutionary diversification during the Pliocene, and many variant forms developed, adapted to varying ecological environments. In North America rhinoceroses became extinct. Camels, some of large size, were abundant and diverse, as were horses. In general, Pliocene mammals grew larger than those of earlier epochs. The more advanced primates continued to evolve in the Pliocene, and it is possible that the australopithecines, the first creatures that can be termed human, developed late in the Pliocene. The land connection between North and South America probably became reestablished in the mid-Pliocene. Species of sloths and glyptodonts, large, armadillo-like, armoured animals, appear in the Late Pliocene fossil record of North America (previously, they had been isolated on the South American continent).