The Upper Triassic period is when dinosaurs first began to roam Earth. Readers explore the world of the first dinosaurs in this book. They learn about giant sea creatures, such as Cymbospondylus, which could grow to become over 30 feet long and incredible reptiles from environments as diverse as forests, riverbanks, and jungles. Computer-generated renderings of these incredible creatures bring them to life in a new and exciting way for readers. A scale shows how these reptiles measure up next to modern humans.