Actually, they ARE!
But the Natural, Peace-pipe smoking, Mother Earth Spirit worshipping NATIVE Americans killed them off after arriving from Asia.
Along with the Mastodon, Mammoth, Giant Ground Sloth, Short-faced bear, American Lion, giant Beaver, Camelops, Glyptodont, dire wolf, pygmy pronghorn, long-horn bison, shrub-ox, and a ton of others.
Who said the Natives didn't love nature's fauna? Well, they sure loved EATING them!
Mmmmm Horses
Actually I don’t like horses