The Vertebral Column (Text–Fig. 3)

The vertebral column of L. hochstetteri has already been described in some detail (E. M. Stephenson, 1952). Further illustrations are included here for the sake of completeness as far as the genus is concerned. At the time of publication of the previous description, the vertebral column of L. hamiltoni had not been examined.

Ritland (1955) has provided a full description of the vertebral column of Ascaphus, with supplementary remarks concerning that of Leiopelma. He includes a discussion relating to the failure of the term “amphicoelous” alone to cover adequately the vertebral condition of Leiopelma and Ascaphus. However, as no completely satisfactory single term has yet been devised to replace “amphicoelous” it seems necessary to retain the latter in order to place the vertebrae of these two genera in a category separate from those of other anurans.

The vertebral column of L. hamiltoni (Fig. 3A) exhibits the essential characteristics already described for L. hochstetteri. The pattern of the vertical column of L. archeyi is also similar except that typically the whole series has a more delicate appearance, with a relatively greater amount of uncalcified cartilage in evidence.

In the vertebral column of the old male specimen of L. hamiltoni illustrated (Figs. 3A, 3C, and 3F), considerable calcification of cartilage and certain bony fusions have occurred. The ribs are partly fused with the transverse processes of the vertebrae concerned, while the characteristic forked and flattened expansions of the lateral extremities of the second pair of ribs, though visible dorsally, are largely fused together.

In all three species, nine presacral vertebrae are present except in occasional cases where fusion of two adjacent vertebrae is obvious. The urostyle has usually at least one pair of well-defined transverse processes developed on the first postsacral vertebra. Of these vertebrae, portions of three may sometimes be distinguished from the dorsal aspect of the urostyle.

The sacral vertebra, as already reported for L. hochstetteri (E. M. Stephenson, 1952), consists of two separate bony halves joined dorsally and ventrally by units of cartilage. This condition, which is not found in Ascaphus, is possibly unique among anurans. In the vertebral column of the specimen of L. hamiltoni illustrated in Figs. 3A, 3C and 3F, the ventral cartilage of the sacral region has remained uncalcified, but the dorsal portion, forming what is in effect the highest point of the neural arch, is seen to be heavily calcified, with possibly some development of bone. It still remains, however, as a discrete element and has been pushed slightly out of position by partial fusion of the two bony halves of the vertebra. Dorsal views of the same region in a mature specimen of L. archeyi and a young L. hochstetteri are provided (Figs. 3B and 3E).

Figure 3D illustrates the condition found in an immature female L. hochstetteri. This should be compared with the photograph of the vertebral column of an adult specimen of L. hochstetteri previously published (E. M. Stephenson, 1955, 610). It is of some interest to note that the uncinate processes typically seen on the most anterior pair of ribs are seen on the second pair in Fig. 3D.

As has already been reported (E. M. Stephenson, 1952, 606), fusion of two adjacent vertebrae is occasionally seen. It seems unlikely that this feature, as far as Leiopelma is concerned, is of any particular phylogenetic significance or that it provides evidence of a tendency towards specialisation. More probably, it indicates the fact that in the populations concerned, such occurrences are of little selective importance.