Of, relating to, or being the epoch of geologic time from about 2.6 million to 12,000 years ago, the older of the two epochs of the Quaternary Period. It is characterized by the alternate appearance and recession of northern glaciation, the appearance and worldwide spread of hominins, and the extinction of numerous land mammals, such as the mammoths, mastodons, and saber-toothed tigers. See Table at geologic time.
The Pleistocene Epoch.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.