The Tyrannosaurus Rex evolved from the King Carp.

The King Carp is a red fish that also has catfish-like filaments around its mouth and wears a golden crown right on its head. The King Carp is very capable of surviving, no matter how dirty the water it is located in, and can live for a long time even on land where there is no water. The King Carp can evolve into the Tyrannosaurus Rex, a dragonlike dragon with a dragonlike appearance that intimidates others, a greenish upward three horns on its head, and a macro-shaped deck on its back.

The evolution of the King Carp comes from the ancient Chinese myth of the Carp Leaping Dragon Gate. Legend has it that the Dragon Gate is located above a waterfall, and in order to become a dragon you need to swim up the waterfall against the current; however, in the game the King Carp cannot learn to climb the waterfall, whereas the King Carp's evolution, the Tyrannosaurus Rex, can learn to climb the waterfall.

The Super Evolution form of the Tyrannosaurus Rex

If the trainer has the Keystone and the Tyrannosaurus Rex carries the Tyrannosaurus Rex Evolution Stone, the Tyrannosaurus Rex can super-evolve into a Super Tyrannosaurus Rex during battle. Super Evolution is an evolution that goes beyond the boundaries of what can be evolved in a Pokémon, and belongs to a higher level of evolution. A super evolved Pokémon temporarily releases its hidden power, and can utilize abilities that it would not be able to do through normal evolution.

This type of evolution only occurs in certain Pokémon. Super Evolution is a temporary state that cannot be maintained permanently. Super Evolution can be used in Generation VI and Generation VII games.

The Super Tyrannosaurus Rex weighs more than the Tyrannosaurus Rex; its racial values for Attack, Defense, Special Attack, and Special Defense have increased; and its trait has changed from "Intimidating" or "Overconfident" to "Broken". The trait has changed from "intimidating" or "overconfident" to "broken".