0点のテストを隠す場所を探していたのび太は、地下に広い空洞を見つける。早速、みんなをつれて地底探検に乗り出すが、楽しく遊んでいる最中にスネ夫がどこかに迷い込んでしまった！
必死でスネ夫を探すのび太たちだったが、人食い人種ナンジャ族に捕らえられてしまい…。
Nobita and Doraemon were finding out the truth about a real dinosaur. Nobita saw something under the ocean when they come across a cave that leads to an underground world full of dino-people. Nobita and his friends are amazed by their new discovery but sadly their memories must be wiped and must return to earth.
