AmphibiaWeb - Ascaphidae


(Translations may not be accurate.)


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2 species in 1 genus

Commonly Called Tailed Frogs

Ascaphus truei
Ascaphus truei
Photo by William Flaxington
(Click for family gallery)

The most striking feature of Tailed Frogs is its namesake or "tail", which is actually the external copulatory organ (an everted extension of the cloaca), used during internal fertilization that takes place underwater in fast flowing streams. The copulatory organ is controlled by the same muscle which controls the wagging of a dog's tail, the caudalipuboischiotibialis (this muscle is only found in this family among frogs). Tadpoles have large sucker-like mouths (gastromyzophory) to aid in clasping to rocks while they feed. Tadpoles may take up to 7 years to metamorphose, although 4 is average. They are small, brown or gray, have reduced lungs, and vertical pupils. Males do not vocalize.

Ascaphids are considered primitive frogs whose closest sister-group is Leiopelmatidae.

These species inhabit cold, fast flowing streams from British Columbia, south to Mendocino County (California) and east to the Rocky Mountains of Idaho and Montana in North America.

Written by AmphibiaWeb

Notable Family Characteristics

  • They are unique in having an external copulatory organ, which gives its name "Tailed Frogs"
  • Fertilization is internal taking place underwater
  • Tadpoles have large sucker-like mouths and live in fast-flowing streams
  • Tadpoles take an average of 4 years, up to 7, to metamorphose
  • Inhabits cold, fast-flowing streams, as adults and tadpoles
  • Some morphological features: 1) 9 presacral vertebrae; 2) sternum cartilaginous, omosternum present; 3) urostyle with one condyle; 4) free ribs present on 3rd, 4th, and 5th vertebrae; 5) pectoral girdle arciferal; 6) clavicle overlies scapula; 7) maxilla and premaxillae contain teeth; 8) sartorious not a separate muscle; 9) aquatic larvae (Type III); 10) presence of caudalipuboischiotibialis muscle; 11) tympanum absent; 12) pupil vertically elliptical
  • Distribution limited to Pacific Northwest and Rocky Mountains of North America
Ascaphidae Richness map

Cartography Credit: Zoe Yoo, UC Berkeley
Range maps sources: AmphibiaWeb, UC Berkeley, and IUCN RedList

Relevant Reference

Nielson, M., K. Lohman, and J. Sullivan. 2001. Phylogeography of the Tailed Frog (Ascaphus truei): implications for the biogeography of the Pacific Northwest. Evolution 55(1):147-160.

Cannatella, David. 2008. Ascaphus. Tailed Frogs. Version 01 December 2008. in The Tree of Life Web Project,

Genus Ascaphus (2 species)
Ascaphus montanus account photos no sound/video
Ascaphus truei account photos no sound/video

Citation: AmphibiaWeb: Information on amphibian biology and conservation. [web application]. Berkeley, California: AmphibiaWeb. Available: (Accessed:

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