THE DEVELOPMENT AND ADULT STEUCTUEE OF THE VEETEBEAL
COLUMN IN LEIOPELMA (AMPHIBIA : ANUEA)
Lynette a. Moffat*
[Accepted for publication 20th Jxine 1973]
(Plates ix-xn)
Synopsis
The development of the vertebral column in an anuran with notochordal amphicoelous
vertebrae, namely the rare, endemic New Zealand frog, Leiopelma, is described for the first time,
and a detailed description is given of its internal morphology in adult stages. Long-standing
claims that the persistent notochord and the absence of ball-and-socket joints in the vertebral
column are primitive character-states in the Anura are upheld, contrary to a recent claim (Inger,
1967) that the ectochordal state of the vertebrae of Leiopelma has evolved secondarily as a result
of neoteny from the holochordal condition found in most other frogs. All the so-called transverse
processes of the vertebrae are pleurapophyses because discrete ribs are present during
developmental stages, and the forked ribs of the third or fourth vertebrae enclose the anterior
lymph hearts. The urostyle of L. archeyi develops from the first four pairs of postsacral neura-
pophyses and the ventral region of the perichordal tube of the first five postsacral vertebrae which
undergoes squamous cell hyperplasia and subsequent metaplasia into hyaline cartilage to form the
hypochord. Factors contributing to the evolution of the short presacral column and long pelvic
girdle in anurans are also discussed.
Although it has been customary to place Leiopelma and the North American genus Ascaphus
in the same family, differences in their vertebral morphology as well as a number of other characters
strongly support Kuhn's (1967) suggestion that these two genera are not closely related. As
Leiopelma and Ascaphus possess a number of character-states which are generally considered
primitive in frogs, it would appear that they are both relics of ancient but otherwise independent
groups within the Anura.
Introduction
Only two genera of living frogs, Ascaphus Stejneger, 1899 from North
America and Leiopelma Fitzinger, 1861 from New Zealand, are known to possess
notochordal amphicoelous vertebrae in adult stages. In other anurans the
notochord is discontinuous if not entirely absent from the adult vertebral column
and the joints between adjacent centra are synovial joints which may be pro-
coelous, opisthocoelous or amphicoelous in shape, the last-named having a free
intervertebral disc. Various aspects of vertebral structure and development
in anurans with synovial intercentral joints have been described by many authors,
including Cope (1866), Gadow (1897, 1901, 1933), Eidewood (1897), Schauinsland
(1906), Beddard (1907), Nicholls (1916), Gilhes and Peberdy (1917), de Gaay
Fortman (1918), Noble (1922, 1924, 1931), Mookerjee (1931), Eamaswami (1933),
Zaharesco (1935), Mookerjee and Das (1939), Al-Hussaini (1941), Hodler (1949a,
1949&), Smit (1953), Stokely and List (1955) and de Silva (1956). Much of the
earher work on anuran vertebrae has been reviewed by Eemane (1936), Devillers
(1954) and Griffiths (1959a, 1963).
The only investigations concerned specifically with the vertebrae of ascaphids
appear to be Eitland's (1955) account of the external and internal morphology
of the adult vertebral column of Ascaphus, van Dijk's (1960) discussion of the
number of vertebrae contributing to the urostyle in this genus and E. M.
* School of Biological Sciences, University of Sydney. Present address : Department of
Histology and Embryology, University of Sydney.
Pkoceedings of the Linnean Society of New South Wales, Vol. 98, Part 3
BioStor
