Mammals, like the other amniotes (reptiles and birds), also appeared after the Permian mass extinction. Mammals would eventually produce some giants, too, but not for almost two hundred million years. Before that, they mostly lived in modest obscurity in the shadows of a world ruled by dinosaurs. Throughout the Triassic, Jurassic, and Cretaceous (from 250 million years ago to 65 million years ago), most mammals were small, burrowing creatures, a bit like modern-day rodents.
