A large body of water separated the present-day North American continent into two halves during most of the late Cretaceous Period, between 95 and 66 million years ago, and because of the seaway linking the Arctic Ocean to the Gulf of Mexico, land animals on one side could not make it to the other, and would therefore evolve independently. One such genus of animals, trapped on the western half, was the horned dinosaur, whose remains have been found in western North America, as well as Asia.
