Horses become grazers
Merychippus grows tall teeth and long legs, and takes up a life on open grass.
- When
- —
- Duration
- 2 million years
- Known to
- ± 1 million years
- Era
- Miocene, Cenozoic
Around 17 million years ago the horse lineage crosses a threshold: Merychippus has high-crowned teeth with cement filling the enamel folds, a design that survives decades of chewing abrasive silica-rich grass, and limbs built for sustained running on hard ground. The change opens the grasslands to horses and triggers the largest radiation in their history — over a dozen genera coexisting in North America. Isotopes in their teeth record the diet switch directly.