This chapter described widespread changes to ocean and land environments, including changes to climates and the rise of flowering plants, that served as catalysts for the spread of dinosaurs and other vertebrates.
1. Continental drift during the Cretaceous Period caused the continued breakup of the northern and southern supercontinents of Laurasia and Gondwana respectively, separating the continents into landmasses approximating their present-day configuration.
2. There was a dramatic rise in sea level during the Cretaceous Period, caused by an acceleration of seafloor spreading that enlarged ocean ridges, formed undersea mountains, and displaced water to areas that were once dry land. Some continental landmasses, including North America, were encroached on by large bodies of water.
3. There were probably no ice caps during the Cretaceous Period, and fossil evidence of plants and animals across the continents from pole to pole strongly suggests that subtropical climates had reached well into the interior of continents of both the Northern and Southern Hemispheres.
4. The dominance of gymnosperms diminished during the Cretaceous Period with the rise of flowering plants—the angiosperms. The ability of angiosperms to grow rapidly and disperse widely allowed them to diversify into hundreds of species by the end of the Cretaceous Period.
5. The rise of angiosperms was accompanied by the corresponding evolution of increasingly efficient and complex dental batteries—adaptations for chewing—in the ornithopod dinosaurs.
SECTION TWO: Saurischian Dinosaurs of the Cretaceous Period
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