Over centuries, discoveries of fossil bones spawned legends of monsters such as giants and dragons. As the field of earth sciences matured during the 19th century, early fossilists gained understanding of prehistoric creatures such as Tyrannosaurus, Triceratops and Stegosaurus. This historical study examines how these genuine beasts morphed in the public imagination into mythical, powerful engines of destruction and harbingers of cataclysm, taking their place in popular culture, film, and literature as symbols of "lost worlds" where time stands still.