Doraemon: Nobita to Ryuu no Kishi

Doraemon built an underground hideout, but Suneo became lost inside. When the others tried to return, the entrance collapsed. They searched for a new way in and ended up in a world with dinosaurs. A soldier named Vanho rescued them and led them to Suneo. They learned that Vanho’s people intended to study Doraemon’s group as test subjects and take over Earth.