Coincidentally, Nobita discovers a fossilized egg of a dinosaur that he hatches with Doraemon's advanced gadgets. They raise it into a mature dinosaur, but understand that keeping it is impractical and return it to prehistoric times. However, their actions reveal a group of hunters from the future who jeopardize the dinosaur population. Intent on safeguarding these creatures, Doraemon and his companions embark on a prehistoric expedition.