PLIOCENE (Gr.irXeIov, more, and 'moos, recent), in geol ogy, the name given by Sir Charles Lyell to the system of strata lying between the Miocene and the Pleistocene. The name refers to the increasing number of living species amongst the fossils of this, the highest division of the Tertiary. The Pliocene is now considered the upper of the two subdivisions of the Neogene or Newer Tertiary period.
During this period the great land masses were approaching the configuration which they exhibit at the present day and the marine Pliocene deposits are limited to comparatively few areas. In Europe the marine re gression which closed the Oligocene was succeeded by a new, but feeble, marine transgression in the Pliocene, which was closed by a final regression before the opening of the Quaternary. Reference should be made to the article on Miocene for the extent of the seas at the opening of the period. The North sea of the Pliocene period covered parts of East Anglia, northern Belgium and Holland, and in the earliest part of the period is believed to have occupied the Thames valley. Bays from the Atlantic covered parts of south-western England and north-western France, and the valley of the Guadalquivir. From the western Mediterranean a bay extended up the Rhone valley as far as the present position of Lyons. Early in the period the sea covered considerable areas of Italy and Sicily, but these lands had assumed approximately their present form by the close of the period. The eastern Medi terranean remained cut off from the west, and the Black sea and Aralo-Caspian sea began to assume their present form. Generally, however, all over the world the majority of Pliocene formations are non-marine, and hence local in their distribution. In many areas the Alpine earth movements did not cease until the close of the period, and not only are the Pliocene deposits represented by vast accumulations of coarse sediment—such as the Siwalik series (Mio-Pliocene) of northern India and the Irrawaddian sands (Mio-Pliocene) of Burma—but these sediments have themselves been severely folded. The formation of some of the great rifts, such as those of East Africa, is attributed to the Pliocene period; volcanic outbursts of the central plateau of France, Etna and the Italian volcanoes, and the East Indian volcanoes probably com menced in this period. In North America marine Pliocene is found fringing the coasts of California and continental deposits are widespread. The oncoming of a glacial era is evidenced by the
lowering of temperature during the period. In Britain the earlier Pliocene seems to have been warmer than at present, but the per centage of arctic or northern species amongst marine fossils in creases as the period advanced.
Sir Charles Lyell defined the Pliocene strata as those which contained from 36 to 95% of living marine mollusca. Although this rule is no longer strictly applicable, the Pliocene marine organisms are very like their living representa tives, and there is often practically no specific difference. Thus most of the existing genera of mollusca have Pliocene representa tives. It is notable, too, that there is often a closer resemblance between Pliocene faunas and the faunas existing in the neigh bouring seas or rivers than there is between Pliocene faunas in widely separated regions.
The mammals of the British Pliocene include Machaero dus (the sabre-toothed tiger), hyenas, dogs, fox, wolf, glutton, marten, bears (lima arvernensis, the grizzly bear and the cave bear), seals, whales, dolphins, bisons, musk ox, gazelle, the red deer and many others now extinct, the roebuck, pigs and wild boar, hippopotamus, hipparion and horse (Equus caballus and E. stenonis), several species of rhinoceros, tapir, hyrax, elephants (Elephas meridionalis, and E. antiques), several mastodons, squirrel, beaver, hare, mice, voles, etc. The mastodon disappeared from Europe before the close of the period, but lived longer in America. Although no generally accepted direct ancestor of man sufficiently advanced to be called human has yet been found in the Pliocene, there are several manlike forms which represent offshoots from the main human tree. Amongst these the most famous are Pithecanthropus erectus, found by E. Dubois in Java, and Eoanthropus dawsoni, found.by C. Dawson at Piltdown in Sussex. Monkeys such as Macacus and Semnopithecus occur in the Pliocene of Europe as well as in the Upper Siwalik of India. During the Pliocene the mammals of North America were able to migrate into South America, and a few of the southern forms travelled northwards: Pliocene Stratigraphy.—The following stages have been dis tinguished in the Mediterranean Pliocene : — Marine Fades Continental Facies 2 Upper—Calabrian Villafranchian
{ Astian facies Lower Pliocene I Lower Plaisancian facies The Pontian, sometimes included as Lower Pliocene, has been considered under Miocene.