Nobita visits a museum on a school trip and locates a stone that looks like a dinosaur egg fossil. Using the Doraemon time cloth, he returns the fossil to its original state and twin dinosaurs emerge from the egg, which he names Kyu and Myu. Nobita raises them without telling anyone, but when they grow up and can no longer stay in his room, Doraemon suggests to return them to their own time. Together with their friends, Doraemon and Nobita embark on a trip to the Cretaceous period where they will live a great adventure on a mysterious island.