The family Ascaphidae is a primitive family as evidenced by a higher than normal number of vertebrae (9 presacral), the vertebrae shape, the presence of ribs and a high chromosome number (Nussbaum et al. 1983). The family is represented by a single living species, the Tailed Frog (Ascaphus truei).  This species is endemic to the Pacific Northwest (Pough et al. 1998).