Ascaphidae are a family of tailed frogs. It only contains two species: Ascaphus montanus and Ascaphus truei and belongs to the suborder of ancient frogs. This tail makes this family distinct to all other frogs, and thus its classification is made difficult. While some agree with its position here, other's think it should be sister to all other frog. The tail is actuall an extension of the male cloaca.
As well as this ancient tail, it has a number of vertebrae higher than that normal to frogs, non-vocalisation and ribs.
They are extremely small (2.5 to 5 centimetres) and found in North America.
Ascaphids were formerly, and sometimes are still, placed in the family Leioplematidae, for which Ascaphidae shares some similar traits with.
Leiopelmatidae is considered closely related to Ascaphidae, the tailed frogs from North America.
Synapomorphies of Pelobatids include a fused joint between the coccyx and the sacrum, exostosed frontoparietals, and the presences of the metatarsal spade.
Historically, both Leiopelma and Ascaphus were grouped together into the Amphicoela based on shared primitive characters such as the presence of free ribs, amphicoelous vertebrae, epipubic cartilages, and the caudalipuboischiotibialis muscle (Green and Cannatella, 1993).
Synapomorphies of Leiopelma include the presence of ventral inscriptional ribs, low diploid chromosome numbers, absence of a horny beak in larvae, and the reduction of the opercular folds during development (Green and Cannatella, 1993).
Phylogenetic significance of the amphicoelous frogs, Ascaphidae and Leiopelmatidae.
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