|Distribution of Ascaphidae (in black)|
The tailed frogs are two species of frogs. The species are part of the genus Ascaphus, the only taxon in the family Ascaphidae (pron.: //). 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.
Until 2001, the genus was believed to be monotypic, the single species being the tailed frog (Ascaphus truei Stejneger, 1899). However in that year Nielson, Lohman, and Sullivan published evidence in Evolution that promoted the Rocky Mountain tailed frog (Ascaphus montanus) from a subspecies to its own species. Since then, the former species has been formally called coastal tailed frog.
General morphology 
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 Archaeobatrachia suborder of ancient frogs, 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.
These frogs are primitive in having a greater number of vertebrae than other frogs, in lacking the ability to vocalise, and in possessing free ribs. They are small 2.5 centimetres (0.98 in) to 5 centimetres (2.0 in) and are found in steeply-flowing streams in Montana, Idaho, Washington, Oregon, and northern California in the northwest United States and southeastern British Columbia.
The tailed frogs share certain characteristics with the Leiopelma, a genus of primitive frogs native to New Zealand, with which they may be phylogenetic sister taxa. The prehistoric Vieraella belongs to the tailed frog family.
General habitat 
The habitat of the Tailed Frog is cold, fast moving streams with cobblestone bottoms. Tailed frogs are mostly aquatic, but adults may emerge during cool, wet conditions to forage terrestrially. Breeding season lasts from May through September, and females deposit their eggs in strings under rocks in fast-moving streams. Larvae take one to four years to metamorphose in the cool, fast-moving mountain streams.
Adults forage primarily terrestrially along stream banks but also occasionally feed underwater. A wide variety of food items taken, including both aquatic and terrestrial larval and adult insects, other arthropods (especially spiders), and snails. Tadpoles consume small quantities of filamentous green algae and desmids. Large quantities of conifer pollen are consumed seasonally by tadpoles.
During the day, adults seek cover under submerged substrates in the stream, or occasionally under similar surface objects close to the stream. Individuals have also been found in crevices in spray-drenched cliff walls near waterfalls. During winter individuals are less active, especially inland, and appear to retreat beneath large logs and boulders. Tadpoles require cool streams with smooth-surfaced stones with a minimum diameter of 55 millimetres (2.2 in). Tadpoles probably spend most of their time attached to such substrates by a large oral sucker. The large, sucker-like mouth parts of the tadpoles are a second distinctive feature of the species enabling survival in turbulent water unsuitable for other frogs. They prefer turbulent water to smooth, swiftly flowing water.
- Zweifel, Richard G. (1998). Cogger, H.G. & Zweifel, R.G., ed. Encyclopedia of Reptiles and Amphibians. San Diego: Academic Press. pp. 84–85. ISBN 0-12-178560-2.
- Gissi, Carmela; Diego San Mauro, Graziano Pesole and Rafael Zardoya (February 2006). "Mitochondrial phylogeny of Anura (Amphibia): A case study of congruent phylogenetic reconstruction using amino acid and nucleotide characters". Gene 366 (2): 228–237. doi:10.1016/j.gene.2005.07.034. PMID 16307849.
- Roelants, Kim; Franky Bossuyt (February 2005). "Archaeobatrachian paraphyly and pangaean diversification of crown-group frogs". Systematic Biology 54 (1): 111–126. doi:10.1080/10635150590905894. PMID 15805014.
- San Mauro, Diego; Miguel Vences, Marina Alcobendas, Rafael Zardoya and Axel Meyer (May 2005). "Initial diversification of living amphibians predated the breakup of Pangaea" ([dead link] – Scholar search). American Naturalist 165 (5): 590–599. doi:10.1086/429523. PMID 15795855.
- Excerpt from Zeiner et al. 1988 describing tailed frogs
- Type information from the American Museum of Natural History
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Data related to Leiopelmatidae at Wikispecies