Some scientists think the Mountain Beaver is the world's most primitive living rodent, similar in appearance and behavior to animals that lived 60 million years ago. They have small eyes and ears and luxurious whiskers, and are, like many other burrowing rodents, armed with good senses of smell and touch. Learn more about the Aplodontia rufa, more commonly known as a Mountain Beaver, in this easy-to-read species overview by the Smithsonian's National Museum of Natural History.