Geographic differentiation increased during the Mesozoic era

The few organisms that survived the Permian mass extinction found themselves in a relatively empty world at the start of the Mesozoic era (248 mya). As Pangaea slowly separated into individual continents, the climate warmed, the glaciers melted, and the oceans rose and reflooded the continental shelves, forming huge, shallow inland seas. Life again proliferated and diversified, but different lineages came to dominate Earth. The trees that had dominated the Permian forests, for example, were replaced by new plants with seeds.

During the Mesozoic, Earth's biota, which until that time had been relatively homogeneous, became increasingly provincialized; that is, distinctive terrestrial floras and faunas evolved on each continent. The biotas of the shallow waters bordering the continents also diverged from one another. The provincialization that began during the Mesozoic continues to influence the geography of life today. By the end of the era, the world and its biota appeared quite modern. The Mesozoic era is divided into three periods—the Triassic, Jurassic, and Cretaceous—the first and third of which were terminated by mass extinctions, probably caused by meteorite impacts.

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Essentials of Human Physiology

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