Eocene epoch | definition of Eocene epoch by Medical dictionary
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Eocene a geological epoch lasting from 54 to 38 million years ago; a subdivision of the TERTIARY PERIOD. During this time extensive planktonic populations of Foraminifera laid down beds of rock (from which the pyramids of Egypt were built), and many groups of mammals appeared for the first time, for example, rodents, whales, carnivores. Britain was still moving northwards. See GEOLOGICAL TIME.