In paleontology, a Zombie taxon (plural Zombie taxa) or the Zombie effect refers to a fossil such as a dinosaur tooth that was washed out of sediments and re-deposited in rocks and/or sediments millions of years younger. This basic error in the interpretation of the age of the fossil leads to its title. The discovered fossil was at some point mobile (or "walking") while the original animal or plant had long been dead. When this occurs the fossil is described as "reworked".