Fig. 4

The evolutionary history of North American rhinoceroses. In the Eocene, they branched into three families, the hippo-like amynodonts, the long-legged running hyracodonts, and the living family Rhinocerotidae. During their evolution, they varied not only in body size and limb and skeletal proportions but also in the number and position of horns (or lack of horns), the details of their teeth, and many other features (after Prothero 2005)