The little horse of the Eocene. Thirty centemetres tall, with hoofed toes and large canine teeth.
Also - grass! Amazingly, through ages and ages of the advancement of most other plant life - lush forests in the Devonian and Carboniferous - the grasses only made their appearance in the early Cretaceous - food for dinosaurs. So by the time eohippus comes along, dinner is ready.