This genus appeared around 20 mya in North America. With a shoulder-height of around 1m it was of a similar size and stature as Parahippus. Merchyhippus was similar to Parahippus and it is difficult to distinguish the fossils from each other as some species of both genera lived alongside each other.
Its molars were high-crowned and covered in hard cement and pronounced ridges and folds formed structured surfaces, suitable for a diet with a higher proportion of grasses. It Is assumed that Merchyhippus lived so some extent in savannah habitats. Like Parahippus, Merychippus carried its weight on the tip of the middle toe; the two lateral toes were reduced but still present. The footpad became reduced and the springy system of supporting ligaments more pronounced. Radius and Ulna fused, so leg rotation became impossible.
Merychippus gave rise to ~20 different species, comprising specialised grazers, but also mixed feeders and browser, which continued to thrive in a variety of habitats.