What changes occurred in the surroundings of the species from hyracotherium to equus?

The changes that occurred in the surroundings of the species from Hyracotherium to Equus are young shoots of trees and shrubs to tough leaves of grasses and wooded swampy areas to plains.

Explanation:

Hyracotherium is the fossil horse which is extinct. It was small and had teeth that were adapted to browsing on young shoots of trees and shrubs. It was adapted to live in wooded swampy areas where more toes were an advantage.

Equus is the present day horse or the modern horse. It is much larger and has larger teeth that are adapted to grazing on the tough leaves of grasses.  The single hoofed toes of the present day horse allow it to travel fast in the plains.