|“||That is one big Sharptooth Swimmer!||”|
— Ducky talking to the others
A Liopleurodon appears in The Land Before Time IX: Journey to Big Water as the sole and main antagonist of the film. It is a Swimming Sharptooth (though pliosaurs are referred to as Sharptooth Swimmers) and is the only Sharptooth to appear in the film.
The Liopluerodon first appears in the opening of The Land Before Time IX: Journey to Big Water, where it is seen jumping out of the water in an attempt to attack a Pteranodon. Fortunately, the Flyer is able to escape the jaws of the Swimming Sharptooth, who then proceeds to swim deeper into the ocean.
Later on in the film, when floods create strange 'new water' in the Great Valley, Mo and the Liopleurodon are trapped in the Great Valley by this new water. He appears in the flooded Great Valley, swimming through the water looking for food. He then heads to the shore, noticing Littlefoot and his friends. He attacks, nearly eating them, but he is tied up by Mo. He later escapes however, 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 film, a scene shows that the Liopleurodon is about to break free from the cave, and he goes on after them.
He reappears near the climax of the film, where he attacks the gang again in a rainstorm, nearly killing them. The gang try to climb up a steep hill by the shore to escape, but due to the rain, it is slippery and they fall back down. Petrie meanwhile flies up into the air to escape, but is struck by lightning and falls towards the water. The sharptooth then catches the Flyer's wing in his jaws, but is hit by a log that fell along with Petrie. Petrie flies out and as the sharptooth recovers, the gang hide inside the log. After listening for a while, Littlefoot looks to get out, but Cera says to be quiet because the Sharptooth Swimmer might still be out there. She is then cut off by the shaking of the log. Then, the Sharptooth Swimmer picks the log up and smashes it into the water multiple times, before throwing it hundreds of feet away.
As he nears the log as they are all sore, Mo comes to the rescue, jumping on the head of the sharptooth. The sharptooth throws him off into the water though, incapacitating Mo for a short time. As the Sharptooth Swimmer nears him, he sticks out his tongue at it and slaps it on the face lightly, and swims away, 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. He has not been seen since.
- How this Liopleurodon 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 though, so there maybe some air holes or pockets of air inside the cave for it to breathe.
- This depiction of Liopleurodon appears to be a homage to the depiction shown in Walking with Dinosaurs in regards to its color palette, although unlike the BBC program, the animal is much more accurately depicted in terms of size.
- This sharptooth's crocodile sound effects were used for most future sharpteeth in the later sequels.