|“||That is one big Sharptooth Swimmer!||”|
— Ducky talking to the others
In The Land Before Time IX: Journey to Big Water floods create strange 'new water' in the Great Valley; Mo and the Liopleurodon are trapped in the Great Valley by this new water. He first appears in the flooded Great Valley, surprising Littlefoot and his friends and nearly eating them. He is tied up by Mo, but he escapes, and soon after an earthshake occurs. When the event of the earthshake scares him away into a cave, large rocks crash down in the entrance of it, trapping him. Because of this, Mo called the earthshake a 'good' one, despite the fact that it separates Littlefoot and his friends from their families. While Littlefoot and his gang continues on forward in the flim, a scene shows that the Liopleurodon is about to break free from the cave, and he goes on after them. He reappears at the end of the film, where he attacks the gang again and nearly kills them. Mo comes to the rescue, seemingly sacrificing himself to save his friends. In the end, both aquatics survive the showdown as Mo hides in a hollow tree, and a sudden sense of attention comes to the Sharptooth when he smells the scent of the Big Water (ocean). He then leaves the river path and swims into the sea.
- The Liopleurodon goes back to Big Water (the ocean), and has not been seen since. It is notable for being one of the few Sharptooth antagonists in a Land Before Time film to survive the events of the movie in which it appears, along with the Velociraptor pack in The Time of the Great Giving and the Sharptooth trio in The Great Longneck Migration.
- How this Liopluerodon can breathe air in an underwater cave long enough to break out of it is unknown. The cave is shown to be only partially underwater.
- This sharptooth may have a rivalry with Mo.
- This depiction of Liopleurodon appears to be a homage to the depiction shown in Walking with Dinosaurs in regards to its color palette.