Horses adapt to open ground
Mesohippus and Miohippus grow larger, drop to three toes, and start developing teeth for tougher food.
- When
- —
- Duration
- 11 million years
- Known to
- ± 1 million years
- Era
- Oligocene, Cenozoic
As forests thin, the horse lineage responds. Mesohippus and its successor Miohippus are larger than their Eocene ancestors, stand on three toes with the central one bearing most of the weight, and have longer legs and slightly higher-crowned teeth. Miohippus also splits into multiple contemporaneous lineages rather than transforming as a single line — a fact that helped demolish the old orthogenetic story of horse evolution as a straight march toward the modern animal.