A flood trapped the sharptooth swimmer and Mo in the Great Valley. It first appeared when the group meet Mo, and Mo sees the Liopluerodon. The sharptooth ignores him and swims towards the group on the surface, and Mo tries to warn the group, who don't know he is trying to warn them.
It finally appears and attacks them, but Mo ties its tail up, but it escapes and swims away. After, an earthquake occurd and traps the Liopleurodon in a cave, but it soon escapes. It follows the group and finally appears at the end when it attacks the group again. It nearly eats Petrie by biting his wing, but a log hits its head. The group hide in the log, so the sharptooth grabs it and throws it away.
As it is about to eat the group, Mo appears and jumps on it's snout, but it throws him away and turns it's attention to him. Mo sticks his tongue out at him and whacks it with his tail, causing it to chase him, causing the group to think Mo died. However, Mo reappears in the morning, telling of how the Liopleurodon found the sea, forgot about Mo, and swims back to it's home.