Dinosaur Adventures Level 1 Reader! How did the dinosaurs die? Which animals first appeared during the Cretaceous Period? How did this time shape the world today? Go back in time 145 million years with The Cretaceous Period and see how the world has changed!Level 1 readers are aimed at children who are starting to recognize common words and are capable of sounding out unfamiliar words. Short, simple sentences help guide the reader through new concepts and ideas.