The Cretaceous Period, from 144 to 66 million years ago, is the youngest division of the Mesozoic era. Modern mammals and birds began to appear during this period, as well as the first flowering plants. The break-up of the super-continent, Pangaea, led to changes in the Earth's climate and regional differences in animals and plants from one continent to another. At the end of the Cretaceous, a mass extinction wiped out the dinosaurs and many other groups of organisms.
Cretaceous features of the United States: