Cave salamanders are amphibians that live exclusively in dark caves deep below the Earths' surface. As a result, they have small, nonfunctional eyes (there's no light in the caves to support vision). Millions of years ago cave salamanders evolved from a salamander species that lived above ground and had large, functioning eyes. The non-functional eyes of cave salamanders are considered: homologous structures imperfect structures pseudogenes vestigial structures.