Cretaceous The final geological period of the Mesozoic era. It extended from about 144 million years ago, following the Jurassic, to about 65 million years ago, when it was succeeded by the Palaeocene epoch. The name of the period is derived from creta (Latin: chalk) and the Cretaceous was characterized by the deposition of large amounts of chalk in western Europe. The Cretaceous was the time of greatest flooding in the Mesozoic. Angiosperm plants made their first appearance on land and in the early Cretaceous Mesozoic reptiles reached their peak. At the end of the period there was a mass extinction of the dinosaurs, flying reptiles, and ammonites, the cause of which may be related to environmental changes resulting from collisions of the earth with large meteorites (see Alvarez event; iridium anomaly).

Cretaceous Third of the three periods included in the Mesozoic Era. It began approximately 145.6 Ma ago and ended about 65 Ma ago. It is noted for the deposition of the chalk of the White Cliffs of Dover, England, and for the mass extinction of many invertebrate and vertebrate stocks. Among these were the dinosaurs, mosasaurs, ichthyosaurs, and plesiosaurs. See K/T BOUNDARY EVENT.

Cretaceous The third of the three periods that are included in the Mesozoic Era, from about 145.6–65 Ma ago. It is noted for the deposition of the chalk of the White Cliffs of Dover, England, much of the chalk being derived from the calcareous plates (coccoliths) of marine algae, and for the mass extinction, at the end, of many invertebrate and vertebrate stocks. During the Cretaceous, angiosperms first appeared (about 120 Ma ago) and by about 90 Ma ago were the dominant plants (at the expense of such groups as cycads and pteridosperms) and woody species evolved. A further major diversification occurred about 65 Ma ago with the development of stratified forests and an increase in the variety of fruits.

Cretaceous The third of the three periods that are included in the Mesozoic Era, about 145.5–65.5 Ma ago. It is noted for the deposition of the chalk of the White Cliffs of Dover, England, and for the mass extinction, at the end, of many invertebrate and vertebrate stocks. Among these were the dinosaurs, mosasaurs, ichthyosaurs, and plesiosaurs.

Cre·ta·ceous / krəˈtāshəs/ • adj. Geol. of, relating to, or denoting the last period of the Mesozoic era, between the Jurassic and Tertiary periods. ∎  [as n.] (the Cretaceous) the Cretaceous period or the system of rocks deposited during it.