Evolutionary stages of the horse:
- Eohippus (Hyracotherium): Small, forest-dwelling ancestor with four-toed front feet and three-toed hind feet.
- Mesohippus: Slightly larger, lived in open grasslands, had three toes on both front and hind feet.
- Merychippus: Further size increase, fully adapted to grasslands, had three-toed front feet and one-toed hind feet.
- Pliohippus: Continued size increase, had three-toed front feet and one-toed hind feet.
- Equus: Modern horse, larger size, fully one-toed, and adapted for running on open grasslands.
