Tyrannosaurus Rex was a carnivore from the dinosaur planet. He was seen in Land Of Dinosaurs. Flounder caught a cold after being stuck in ice. Flounder told Ariel that he doesn't want some of the dinosaurs to look like this, the carnivore and Ariel thinks he's smiling. Ariel was going to do it. Ariel uses her father's trident and it hits the ice and it melts. It frees an adult Brontosaurus with her juvenile, a huge male Tyrannosaurus Rex, a huge adult Triceratops, and a male Stegosaurus. The Tyrannosaurus Rex becomes hungry. He spots his mortal enemy: the Stegosaurus, unlike Triceratops. The 2 dinosaurs battle each other and the T-Rex hits the trident and the trident falls into a trench.

The Tyrannosaurus goes after Ariel and Flounder and they think that if they swim, the dinosaurs won't get them. However, the Tyrannosaurus can breath on land and sea as he is shown aquatic. The trident beam must have gave the dinosaurs aquatic powers when they were unfrozened.

The Tyrannosaurus, Stegosaurus, and Triceratops go on a rampage in the vacation area and Sebastion almost got crushed by the T-Rex. The T-Rex thinks some objects are prey, the carnivore eats everyting in his path. A family of humpback whales came and they scare off the Stegosaurus and Triceratops. The Tyrannosaurus Rex battles the whales, but one huge male hits the T-Rex with his tail and it knocks out the dinosaur. Ariel thanks the whale for rescuing everyone. The Tyrannosaurus couldn't stand anymore of whales so he heads back to land with the Triceratops, the Stegosaurus, and the Brontosaurus family.