Miohippus (meaning "small horse") (whose species are commonly referred to as the three-toed horses) was a genus of prehistoric horse that lived in what's now North America during the late Eocene to early Oligocene Period some 36 million years ago. It's believed to have branched off from Mesohippus, and the two coexisted for about four-eight million years. Mesohippus had died out by the mid-Oligocene, and Miohippus became much larger than it. They weighed around 40 to 55 kilograms. They were so… (More on Miohippus)