The fascinating lives and puzzling demise of some of the largest animals on earth.Until a few thousand years ago, creatures that could have been from a sci-fi thriller—including gorilla-sized lemurs, 500-pound birds, and crocodiles that weighed a ton or more—roamed the earth. These great beasts, or “megafauna,” lived on every habitable continent and on many islands. With a handful of exceptions, all are now gone.What caused the disappearance of these prehis...