How did the ecological changes force horses to change?

The horses were forced to evolve because of the changes in the environment. After the climate changed, the forests change into grassland and open prairie. The horses toes turned into hooves, so they will have greater ability to run in the prairie. The horses teeth increased in size to make grass easier to chew. All of the physical changes of the horse are ways that the horses adapted to the changing environment over time.(www.amnh.org)