Horses evolved in North America, and the Hagerman Horse, Equus simplicidens, is the first true one-toed horse. It is the best known fossil at Hagerman, where fossil evidence has been found for more than two hundred species. These Pliocene fossils include saber-toothed cat, mastodon, bear, camel, ground sloth, and smaller animals such as rodents and frogs, and their scientific study is central to Hagerman.