Megacerops
Imagine the great cracking sound that must have thundered across North Americas plains when Megacerops males fought in head-to-head combat. These rhino-like creatures have awesome Y-shaped horns with blunt ends perfect for smashing into a rival that's eying your female. As grazers, Megacerops herds could be brought back and unleashed on their old grounds.
Image: Dmitry Bogdanov/Wikimedia