The Jurassic Period (201-145 million years ago) was a major interval of the Mesozoic Era characterized by the diversification of dinosaurs and the breakup of the supercontinent Pangaea into Laurasia and Gondwana. This period saw the dominance of long-necked sauropods, stegosaurs, and large carnivores like Allosaurus. The first birds evolved from small therapod dinosaurs, and marine reptiles such as ichthyosaurs and plesiosaurs flourished in the warm shallow seas.