The tailed frogs are two species of frogs in the genus Ascaphus, the only taxon in the family Ascaphidae /æˈskæfɨdiː/. The "tail" in the name is actually an extension of the male cloaca. The tail is one of two distinctive anatomical features adapting the species to life in fast-flowing streams. It is the only North American frog that reproduces by internal fertilization.