Dinosaur World was worldwide before anyone was born (except for the Undefeatables). Dinosaurs ruled the world. Eventually, a gigantic meteor came in, and blew up almost every dinosaur. Only the ones in Africa, who had a bomb shelter prepared, survived.
The dinosaurs eventually grew stupid as the humans came in, and decided it was their turn to take over. Some of the humans were generous enough to make a reservation for these dinosaurs. They were actually just scared of the dinosaurs, but Nobody said that.
The dinosaurs now live in Dinosaur Land, because it is awesome for dinosaurs here. It is just another dangerous location that can be found in the dreaded UnUniverse.