Interesting theory on the evolution of teeth.
I've never looked specifically into how teeth developed, never gave it much thought at all to be honest. There are two basic schools of thought though on how teeth developed in fish. One is that they started out inside the mouth and gradually worked there way into the mouth. The other is that they developed in the pharanyx , yeah I had to look it up to.
It's especially interesting that much like with many things in evolution it appears plausible that whatever teeth originally developed to do wasn't to be a tooth, though clearly they are better at being teeth than whatever else they originally developed to do.
I've never given it much thought, either, but this was an interesting article. Kind of creepy and scary, but interesting just the same! Teeth on the outside of a fish to grab prey so they can swallow it whole, then the whole evolutionary process with the teeth on the inside....wow.