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The Mesozoic Era covers an interval of Earth history from about 230 to 65 million years ago, comprises three geologic time periods: Triassic, Jurassic, and Cretaceous. The term, meaning middle life, was introduced in 1841 by the English geologist John Phillips. In most places the rock layers deposited during the three eras are separated from one another by unconformities, breaks in the sequence of deposition of the geologic record.
This is the time during which the world fauna changed drastically from that which existed in the Paleozoic. Dinosaurs, which are perhaps the most popular organisms of the Mesozoic, came to being in the Triassic Period, but many diversity in their breed was not to be seen until the Jurassic Period. Except for birds, dinosaurs became extinct at the end of the Cretaceous Period. Some of the last dinosaurs to have lived are found in the late Cretaceous deposits of Montana in the United States.
LIFE
Marine invertebrate life during the Mesozoic was dominated by the Mollusca, of which the ammonites were the most common. Other important invertebrate groups were the bivalves, brachiopods, crinoids, and corals.
The vertebrates of this era were dominated by reptiles, as mentioned, the dinosaurs. All the major groups of living forms were established by the Triassic, and this period marked the spread of these reptiles into almost every major habitat on Earth. The dinosaurs perished at the end of the Cretaceous. Mammals evolved from therapsid reptiles during the Triassic, and the first birds appeared during the Jurassic.
Mesozoic plants consisted mainly of ferns, gymnosperm orders of cycads, ginkgos, and conifers. Angiosperms, which may have first appeared in the Triassic, were firmly established by the end of the Mesozoic Era.
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