Ok, wow. I just sent you a website listing EVERY genus of horse ever, and you're still arguing about teeth? Don't you think that was one of the first possibilities considered when they discovered these fossils? Or do you think scientists are slobbering idiots who haven't thought of what you have?
As for the site: It does nothing but induce doubt from the start. Constantly using phrases like "so-called" and "assuptions", on things that are true. Also apart from that, ALL OF THE INFORMATION IS OUTDATED. The most recent date on the site is 1996, and that date doesn't even concern where they got their information from! The thing most creationists don't realize is that Science, when it proves itself wrong, is willing to accept the correct answer, and change. Unlike religion, which hasn't change for a good 400 or 500 years....or more.
Fact 1. Did it ever occur to this "researcher" that the Ice Age had moved the placement of the fossils? Ice and glaciers covered nearly 70% of the earth, and moved massive amounts of land.
Fact 2. It isn't circular reasoning. The writer used a big word to try and confuse you. Great tactic.
Fact 3. Adaptation is a large part of evolution. Did it not occur to this writer that the primitive horses were simply adapting to their enviroment? Really, things like numbers of ribs and vertabrae don't matter, chalk it up to adaptation.
Fact 4. It seems as if the writer failed to realize that evolution occurs in one of three ways. 1. the original creature evolves into an "upgraded" version of itself(the earlier moth example), and 2. the original creature evolves into two or more similar creatures(dinosuars into reptiles and birds), and 3. creatures evolve from one creature, the original creature remains almost unchanged, but the evolved creature stems away from it(humans and apes).
In the case of the horse, option 2 happened. We have the little horses, and we have the larger horses.