What happens as unfavorable environmental conditions persist for plants and animals is that their numbers dwindle. In the case of Pleistocene mammals, changing conditions would cause them to seek areas still favorable to them, allowing them to survive there. As these areas became ever more restrictive, their numbers would continue to decrease. Finally a breeding population could no longer be maintained, and the species would then go extinct. Before extinction occurred, though there would possible be some individuals that might be fossilized. But the greatly reduced numbers of individuals would mean very few if any fossils would later be available for discovery. They might go undetected for very long periods of time.

So it’s certainly possible, even likely, that small populations of now extinct animals lived on for hundreds, or even thousands of years after the most recent fossil of their kind was dated. This helps explain why occasionally younger-aged fossils of a particular species are discovered. The fact that the last remaining animals of a given species would probably be living in a relatively small area (or areas) further diminishes the chance of finding their fossils. And finding a fossil that represents the last of its kind, would be millions of times less likely than winning the lottery! Nevertheless, with more and more searching for fossils, as is now going on at an accelerated rate, chances of finding rare fossils has improved. With this in mind it should not be a surprise that Book of Mormon peoples could have known as well as tamed or domesticated now extinct animals.