Subfossil bones of the frog Leiopelma in New Zealand

Abstract

The subfossil frog fauna, primarily from cave deposits, was examined from throughout New Zealand. Frog bones are recorded from 119 sites between Kaitaia and Fiordland, but are most common around Waitomo and northwest Nelson. Three new species of leiopelmatid frog are described. Leiopelma n.sp. 1 and Leiopelma n.sp. 3 are represented by thousands of bones representing a minimum number of 341 and 212 individuals respectively. Leiopelma n.sp. 2 is known only from 31 bones of 1 individual. A minimum number of 107 individuals of L. hamiltoni and 33 L. hochstetteri were recorded, greatly extending the range of these species so that the former is known to have occurred as far north as Waitomo and the latter as far south as Punakaiki. The distribution of Leiopelma n.sp. 1 was New Zealand wide, that for Leiopelma n.sp. 2 limited to Fiordland and that for Leiopelma n.sp. 3 to the North Island. Subfossil material of L. archeyi was not found. Leiopelma n.sp. 1 was an extremely stout, medium length frog (50 - 60mm SVL) which was probably a walker, rather than a hopper, that occupied a terrestrial niche on the forest floor. In comparison Leiopelma n.sp. 3 was a large species (up to 100mm SVL) which was relatively the best jumper in the genus, and was probably a streamside inhabitant in forested areas. The contention that L. archeyi is a neotenic form of L. hamiltoni is found to be false with both species exhibiting similar degrees of ossification. Other than size these species are osteologically identical. Clinal size variation which has a direct relationship with increasing latitude was observed in Leiopelma n.sp. 3, L. hochstetteri and to a lesser extent, Leiopelma n.sp. 1 and L. hamiltoni. Those species that had more aquatic tendencies had the greatest size variation. It is suggested that larger size is the result of arrested development due to lower temperatures. Terrestrial species by a combination of habitat selection and behavioural adaptations can evade the lower ambient temperatures. An osteological comparison of all Leiopelma species was made and these compared to Ascaphus. The recognition of the family Leiopelmatidae as separate to the Ascaphidae is supported. The dichotomy among the extant Leiopelma species is mirrored among the extinct forms with Leiopelma n.sp. 1 and Leiopelma n.sp. 2 being related to L. hochstetteri and Leiopelma n.sp. 3 to the L. hamiltoni/archeyi lineage.