The existence of the visible "tail" appendage makes this frog family distinct from all other frogs. Thus, its wider classification is difficult. It is usually classified in the ancient frog suborder Archaeobatrachia, though some say it should be a sister to all other frogs. The "tail" is found only in males, and is actually part of the cloaca, used to insert sperm into the female during mating. This anatomical feature improves breeding success by minimizing loss of sperm in the turbulent, fast-flowing streams inhabited by this species. Thus, the tailed frogs exhibit internal fertilisation, rather than the external fertilisation found in other frogs.