They seem to have not counted ergots and chestnuts on the legs, as more vestigial toes. Most folks know modern horses descended from mammals that had multiple toes. The toes seem to have not been needed, so more weight went onto one toe to create the hoof as we now know it. Horses could run faster, longer, using the hoof structure instead of toes.
Mother Nature tried a number of pre-horse body designs, went with the most successful in surviving. One of the tar pit excavations showed almost 15 types of pre-horse skeletal remains with various foot and hoof designs. All were living about the same time, perhaps even together, by their locations in the tar-preserved, dead animal piles. I was surprised, thinking evolutionary changes would be much futher apart in years! I think I read that information in the Smithsonian magazine.
