The evolution of the horse, from prehistoric times to the modern-day show ring, reflects a changing environment and increasing human intervention. Scientists can see this in horses' bones, hooves, DNA, and even teeth.

The complexity of enamel structure in horses’ teeth tells an interesting story about how horses evolved and, by studying equine teeth from different eras, researchers can see how the animals adapted to different grazing lands, as well as to domestication, said Nicholas A. Famoso, PhD candidate in the Department of Geological Sciences at the University of Oregon in Eugene.

“Investigating the evolution of horse enamel in North America has shown that horses had been increasing the amount of enamel in their teeth to combat the increasing amounts of grit in their diets,” Famoso said.

That “grit” comes from dirt and dust associated with pasture and grassland forage, he said. It’s like us eating fresh lettuce that hasn’t been washed well enough, and we find ourselves crunching on something gritty and sand-like