The Cretaceous Period was a period of the Mesozoic Era of Earth's distant past. This was part of Earth's Prehistory, in which there were no written records. There were also many creatures on the planet at this time that are now extinct, such as the Pteranodon, Triceratops, Anatosaurus, and Tyrannosaurus Rex. Jack and Annie visited this time once in Dinosaurs Before Dark. This was both the first and oldest time period Jack and Annie ever visited.