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Ventral view of a cleared and stained skeleton of Leiopelma hamiltoni. Note the inscriptional ribs which are visible as four blue, inverted V-shapes in the abdomen.
There are only four living species of Leiopelma (family Leiopelmatidae), and these are the only native frogs in New Zealand. Human occupation has reduced the range of these species. Leiopelma archeyi is restricted to the Coromandel Range. Leiopelma hamiltoni is known from Stephens Island, and L. pakeka from Maud Island. Leiopelma hochstetteri remains from a few isolated localities on the North Island. However, three other recently extinct species are known from cave deposits in karst limestone regions of the North Island, and the genus was more widespread until Recent times.
Adults of the living species reach a maximum size of about 50 mm. However, the subfossil Leiopelma †waitomoensis reached approximately 100 mm in snout-vent length. Leiopelma are terrestrial and are found under stones and logs in damp areas. They lay their eggs in these damp areas rather than in pools of water. Rather than having aquatic tadpoles, their embryos undergo a more "direct" development to froglets. In Leiopelma hamiltoni and L. archeyi, the male sits over the eggs until they hatch; the froglets, still with a tail, climb up on the male's back and complete development there. In Leiopelma hochstetteri, the larvae move into nearby water after hatching, and there seems to be no direct parental care.
Leiopelma is unique among living frogs in having elongate cartilages in the muscles of the abdomal wall, called inscriptional ribs (the four blue inverted-V cartilages in photo); the function of these is unknown. Like Ascaphus truei, Leiopelma retains certain primitive features such as nine vertebrae in front of the sacrum, and "tailwagging" muscles. These features do not indicate a close relationship, however. Molecular phylogenetic studies indicate that Ascaphus and Leiopelma are highly divergent.