In New Zealand we currently have four species of native frogs and three species of introduced frogs. The Global Amphibian Assessment recently listed all New Zealand's unique native species (genus Leiopelma) as well as two of the introduced species (the Bell frogs Litoria aurea and Litoria raniformis) as threatened or endangered. Hamilton's frog (Leiopelma hamiltoni) on Stephens Island is one of the rarest frogs in the world, with a population estimate of about 300 individuals.
New Zealand's native frogs (pepeketua) belong to the genus Leiopelma, an ancient group of frogs that have changed very little in the last 70 million years. These frogs are found only in New Zealand, and three species are now extinct (L. auroraensis, L markhami and L.waitomoensis), with only four species extant: L. archeyi, L. hamiltoni, L. hochstetteri and L. pakeka.
Members of the genus Leiopelma exhibit a number of primitive traits that separate them from most other species, including: vestigial tail-wagging muscles, cartilaginous inscriptional ribs, the presence of amphicoelous vertebrae, and nine presachral vertebrae (most frogs have eight). Ascaphus truei, the tailed frog of the North-western United States, is the only other extant frog known to possess these features. In addition, there is some evidence to suggest that Leiopelma evolved from an ancestor with ‘normal’ tadpole development and the degree of cranial remodelling that occurs in Leiopelma larvae at metamorphosis is intermediate between salamanders and Ascaphus.