Brontotherium was an enormous beast that roamed the plains of North America about 40 million years ago. They looked like rhinoceroses, only much bigger, and had all these great, weirdly shaped snout horns. The plains indians found their fossilized skeletons sometimes, exposed by erosion. Lots of brontotheria were buried by volcanic eruptions over the eons in the North American plains. I think the name comes from a Lakota word, but I could be wrong. They called them thunder horses or thunder beasts, for rather obvious reasons. Unfortunately, humans and brontotheria missed each other by many many millions of years. I think the closest thing to a human around the time the thunderbeasts roamed the earth was a tree shrew. Surely it quivered with terror when they rumbled past.