Aplodontia Rufa -

Meet the Aplodontia rufa , a creature that is neither a true beaver nor exclusively a mountain dweller. More commonly known as the or "Boomer," this elusive rodent is a true "living fossil"—the only surviving member of its taxonomic family, Aplodontiidae , with roots dating back over 25 million years. Why Is It So Unique? Mountain beaver | Washington Department of Fish & Wildlife