The Tylosaurus is a mosasaur that appears in the episode "Lost and Found."
It is a long, slender light blue reptilian with dark blue spots and lime fins, including a tail fluke. It also has a long snout with a mouth full of sharp teeth.
Role in episode
At the end of the episode, when SpongeBob gives back the little boy his teddy fish, he declines SpongeBob's offer and says he has a new thing to look forward to, which is a Tylosaurus, and then plays with it. The Tylosaurus then appears inside the Lost and Found, which Squidward is still in, and the latter gets scared of the animal.