"Irish elks" are a nice example of an animal which didn't go extinct, but rather its genetic expression simply changed when Earth electric environment changed. Their offspring simply looked different suddenly -- they looked like modern elks today do. So, no massive die-off of, just a change in how the animal looked. Modern elks thus are "Irish elks", there's no difference in the animal itself, just the environment. If for some reason Earth's electric environment would return to the way it was when "Irish elks" existed, then our current elks would start looking like "Irish elks".