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The Triassic Period is the first period of the Mesozoic Era, a span of time from 245 million years ago to 66 million years ago. Although the Mesozoic era commonly known as the "Age of the Dinosaurs,', it should be pointed out that there were other important evolutionary developments taking place such as the appearance of the first mammal birds and flowering plans. The onset of the Mesozoic Era, the Triassic Period, was also a time of profound tectonic activity affecting the entire North American craton. In the east, the primary event was the breakup of Pangea and the formation of the Atlantic Ocean. In the west, it was the formation ofan Andean-type continental margin as the newly-formed continent of North America rapidly moved westward in response to the opening of the Atlantic Ocean coupled with the addition of exotic terranes to the western margin of the continent.. As the Atlantic oceanic ridge rose, the volume of ocean waters that was displaced was sufficient to result in the most extensive flooding of the continent by an epeiric sea since the Paleozoic; a sea whose presence was recorded by the accumulation of extensive carbonates throughout the continental interior. In the oceans, new life forms evolved to fill the vacancies brought about by the Permian extinction. When life returned, however, most of the old forms were gone and an assemblage comparable to those living in our modem oceans took their place. Without doubt, the Mesozoic era was the time of the reptiles with reptilian forms dominating nearly every eco-system from the ocean to the land to the air. But it was also the time of significant changes in the plant community with the flowering plants evolving before the end of the Cretaceous along with a tremendous increase in the kinds and numbers of pollinating insects. The Mesozoic Era ends with the a mass extinction, second only to the Permian extinction.

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