Liopleurodon ferox

Well, it WAS gonna be called The Leviathan of Bloodbath Lake," but the numer of allowed characters stopped right before the final "E."

Liopleurodon ferox, the 50-foot sea monster... I mean, pliosaur. Well, the dinosaurs don't know pliosaurs from a hole in the ground, so to them, he's still a sea monster. His patterning is based on loons, but is used to trick pterosaurs into thinking his back spots are really schools of fish. I also considered a red coloration, but most modern sea predators have some kind of light-against-dark coloration (Orcas, Great White Sharks), so I stuck with that idea. I might make the Peloneustes green.

There's a storyline I've brainstormed where one of these behemoths is trapped in a lake, along with a whole bunch of Peloneustes (smaller, swifter pliosaurs with equally angry teeth), that eats anything foolish enough to go swimming. The herd has to cross the lake during their migration, but when Clay and Rigel get pulled under, their traveling mates must save their lives before they're consumed by... The Monsters of Bloodbath Lake!