What is the biggest change in skull anatomy that occurred from the dawn horse to the modern horse?

I have two answers im not sure which one u want.

1- the sizes are exactly different between modern and dawn horse. it has increased in size. Dawn horse had feet and modern horse had hoovers.

2-increase in the size of the skull; a shift from cusps to complex ridges on the grinding surface of the premolars and molars, elongation of the face and of the space between the incisors and cheek teeth, an anterior shift of the cheek teeth so they lie forward of the eye, a deep lower jaw bone.

answer; i believe the correct answer to the above question is ( friction)