also the archaeologist who investigate things like this!
I'm completely ignorant on such things, so I'll ping the only American archaeologist that I know of here and ask him.
Coyoteman, sorry to bother you, but I need your disinterested expertise here for a bit. Can you verify restornu's statement that horses are native to the Americas and died out sometime after 100 AD? (Restornu, I don't know what year the last mention of horses corresponded to in the Book of Mormon, so the year I picked is a WAG. If I'm far off, will you correct me?)
Going from memory, there was a native horse species in the New World. It was different from our modern horses (same genus, different species, I think). It died out with the Pleistocene fauna. I am not sure when the last one was killed and cooked and eaten, but I believe remains have been found as recently as perhaps 10-12,000 years.
Hope this helps. I would have to hustle some books for a better answer. I have Martin's Twilight of the Mammoths here, so if you need more let me know.