The Triassic Period was the first Mesozoic period. The world was recovering from the great Permian Extinction and more than half the earth's life were the mammal-like reptile Lystrosaurus. These animals soon began to evolve into more species. As life recovered, reptiles, such as Euparkeria, started walking on two legs, an adaptation that increased speed. These features soon gave rise to the dinosaurs, which evolved in the middle Triassic. Reptiles also started to call the sea home, and the same with the air. Protomamals evolved from synapsids. These were the first steps toward worldwide animal domination.