Ultimasaurus is a hybrid from the cancelled Kenner toy line Jurassic Park: Chaos Effect. It is made from the DNA of Tyrannosaurus rex, Triceratops, Velociraptor, Ankylosaurus, and Stegosaurus, making it a deadly fighting machine.
Its appearance gives it the frill and horns Triceratops, head and body of a Tyrannosaurus, the arms and legs of a Velociraptor, the back armor of an Ankylosaurus, and a spine-tipped tail of a Stegosaurus. Its skin is primarily gray with a light yellow underbelly, black stripes on its back and armor plating, yellow markings surrounding the eyes, and a red head and feet. The way the lime green eyes are placed on the head gives it the binocular vision of a Tyrannosaurus. It was bred to be the most deadly of all the Chaos Effect hybrids, but proved to be extremely unpredictable. Unfortunately, the figure was never released due to the fact that the Chaos Effect line sold poorly and some rumors also state that the horns were too long and sharp. However, an infant Ultimasurus did come with one of the human action figures in this toy line, perhaps as a reference to Junior from The Lost World: Jurassic Park. An image of Ultimasaurus can be seen on many figure card backs, referencing that it would have had movable jaws and claws.