I keep wondering if this is somehow a Mormon reference.
For those not in the know, the Book of Mormon depicts ancient Americans riding horses centuries before horses were introduced to the continent by European colonists. So one of the Mormon apologists tried to wrangle out of it by saying Joseph Smith simply used the word horse to make it sound more familiar to his readers when in the original language of the BoM it referred to another animal native to the Americas. When asked what animal, he came out with tapirs. So ancient Native Americans rode to battle on tapirs, according to this BoM interpretation.