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Taxonomic Position of Leiopelma
Noble (1922) referred Leiopelma and its North American relative, Ascaphus truei Stejneger to the family Discoglossidae. In 1924, however, he proposed a new family, the “Liopelmidae” to include Leiopelma and Ascaphus. In 1931, he placed this family in a separate sub-order Amphicoela at the base of his anuran classification. He justified this arrangement by the fact that Leiopelma and Ascaphus are the only living genera of frogs to possess amphicoelous vertebrae and that they retain two tail-wagging muscles, the pyriformis and the caudali-pubo-ischiotibialis, even though neither genus possesses a tail in the adult stage. Noble's recognition of the primitive character of Leiopelma has been supported by more recent anatomical studies, including work on the cranial morphology (Wagner, 1934 b; E. M. Stephenson, 1951, 1955); the circulatory system (E. M. & N. G. Stephenson, 1947; H. Szarski, 1951); development (N. G. Stephenson, 1951 a, 1951 b, 1955); the skeleton.
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(Stadtmüller, 1924; Trewavas, 1933; de Vos, 1938; E. M. Stephenson, 1952; Ritland, 1955).
The familial name Ascaphidae Féjévary 1923, as originally defined contained only Ascaphus truei Stejneger 1897, and predates Noble's Liopelmidae (1924), which contained both Liopelma Günther 1868 laps. cal. = Leiopelma Fitzinger 1861 and Ascaphus Stejneger 1897. Noble (1924), however, stated in a footnote that he followed present day custom in using the oldest generic name in forming the family name.
N. G. Stephenson (1951 b, 18) pointed out that in deriving the familial name Noble formed it wrongly from the root and that its more correct form, which would also incorporate the original spelling of Fitzinger (1861), would be Leiopelmatidae.
The present weight of knowledge of the two genera suggests to the authors that a further step, the separation of Noble's sub-order Amphicoela (Noble, 1931, 485) into two families, Leiopelmatidae (Type Genus: Leiopelma Fitzinger, 1861) and Ascaphidae (Type Genus: Ascaphus Stejneger 1897), would be desirable. Discussion of the anatomical details leading to this proposal is, however, outside the scope of the present paper.