IntroductionCretaceous period (krĭtāˈshəs) [key], third and last period of the Mesozoic era of geologic time (see Geologic Timescale, table), lasting from approximately 144 to 65 million years ago. The Cretaceous was marked, in both North America and Europe, by extensive submergences of the continents. Changes both in the earth's surface and in its flora and fauna brought the Mesozoic to a close.
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