Suneo shows a fossil of dinosaur claw to everyone except Nobita. Being angry, Nobita claims he will be able to find a living dinosaur. As Doraemon refuses to help him, he digs on a hillside, but instead earns punishment from a landlord nearby who forces him to unearth a hole in the ground. He finds an egg-shaped stone underneath and quickly uses a time wrap to return it to its former form and after warming it, the egg hatches to reveal a plesiosaur, who is subsequently named Piisuke by Nobita. Instead of immediately showing it to the others, Nobita waits it grow while making a deal with others. As Piisuke grows too large and is in danger of being found, Doraemon and Nobita transport him to 100 million years ago in the Late Cretaceous period. They are attacked by a mysterious assailant who previously tried to make a deal with Nobita to sell Piisuke, though they manage to escape. Left with no proof, Nobita instead shows them Piisuke through a television monitor, but realizes that he and Doraemon had unknowingly transported Piisuke to the North America shore after the time machine was attacked by the assailant. They and the others decide to go there, but the time machine is overloaded and crashes off.