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THE PHYSICAL WORLD OF DINOSAURS - INTRODUCTION The Mesozoic world of the dinosaurs was much different than today. Continents differed in their size and configuration, climate was warmer, and vegetation, while composed of familiar plants, differed with respect to the dominance of plant types. Here we examine the physical environment of the Mesozoic so we can later view dinosaurs in their natural context. - THE PHYSICAL WORLD OF DINOSAURS PLATE TECTONICS AND DINOSAUR DISPERSAL Dinosaurs evolved during the Late Triassic when the continents were still united as the supercontinent Pangaea and surrounded by the Panthalassa Ocean. Although Pangaea was beginning to rift apart in the Triassic (see Topic 7), the still connected continents facilitated widespread dispersal of the dinosaurs. Although the oldest dinosaurs may have first evolved in South Africa or Madagascar, dinosaurs appeared almost simultaneously in North America, South America, Africa, and India. Clearly, plate tectonic events did not inhibit early dinosaur dispersal. The Tethys Seaway divided Africa from Europe in the Middle Jurassic, separating African dinosaurs from their cousins to the north. Later in the Jurassic, the Tethys became circum-tropical, separating all northern (Laurasian) from southern (Gondwanan) continents. During the Cretaceous, the final period of the Mesozoic, South America, Africa, India, and Australia-Antarctica had become island continents. A land connection existed between Europe-Asia and North America throughout the Mesozoic, allowing east-west dispersal of dinosaurs when sea level did not flood the connections. PALEOGEOGRAPHY OF NORTH AMERICA TRIASSIC The southern and eastern margins of North America were still mountainous as a consequence of the collisional events (with Africa and South America) that brought Pangaea together during the Late Paleozoic Era. Triassic rifting along the east coast produced rift basins that were the home to dinosaurs. The Connecticut River Valley is a remnant of one of those rift valleys and has abundant dinosaur footprints. Elsewhere, to the west of the Appalachian uplift, and to the north of the southern Ouachita Mountains, the interior uplands extended to just beyond the position of the present Mississippi River.
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In the west of Canada (west of Hudson Bay) and the central and western United States (the Plains and Rocky Mountain regions) there was a lowland region sloping to the west. Mature rivers drained across the lowland, providing habitat for dinosaurs. During the entire Mesozoic, most of the region now occupied by California, part of Nevada, Oregon, Washington, British Columbia, and Yukon; was not yet a part of the continent. For most of the Mesozoic, subduction occurred along the western margin of North America causing the formation of volcanic arcs and numerous collisional events of volcanic arcs and microcontinents. By the end of the Mesozoic, these collisional events created new continental crust in the far west. For the reign of dinosaurs though, the far
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