SPHENOPHRYNE - American Museum of Natural History

2000 ZWEIFEL: PARTITION OF SPHENOPHRYNE
103
Fig. 60. Lateral view of right ear of Austrochaperina
brevipes (AMNH A130527, anterior to
right). Cartilage stippled, bone clear; c columella,
s squamosal; scale line spans 2 mm.
too literally, as accurate depiction depends
on having the premaxillary shelf exactly horizontal
when drawn, an ideal not readily
achieved with such tiny bones.
The presence or absence of teeth or serrations
on the labial margin of the premaxillae
is discussed in the following section on
dentition.
I regard the elongate shelf with little emargination
and vertical ascending processes as
derived features indicative of a close relationship
between O. alpestris and O. stenodactyla.
No such clear relationships appear
in the apparently plesiomorphic features of
the premaxillae of the other species, although
O. coggeri is suggestively closer in morphology
to alpestris and stenodactyla than to
the others.
DENTITION: Parker (1934: 3) stated that in
the Microhylidae, maxillary ‘‘teeth may be
present or absent, but when present are usually
well developed and of the normal Salientian
pattern; in Sphenophryne cornuta
alone have they been discovered in a vestigial
condition.’’ Those microhylids that pos-
sess ‘‘normal’’ teeth include all members of
the Dyscophinae (Madagascar and southeast
Asia) and most species of Cophylinae (Madagascar).
In these groups there often are teeth
on the vomer as well.
Typical maxillary and premaxillary frog
teeth are elongate, tubular structures with a
basal pedicel and a distal crown attached to
the lingual surface of the bone in pleurodont
fashion (Parsons and Williams, 1962: figs. 3–
4, 7). Teeth of no genyophrynine microhylid
match this description, but in several species
studied here, as well as in some Cophixalus
(Zweifel, 1985b) there are toothlike maxillary
and premaxillary structures. Any such
structures on the vomer are more clearly
odontoids or serrations.
Among cleared-and-stained specimens of
19 species I examined, 11 have smoothedged
maxillary and premaxillary bones with
no trace of teeth: Austrochaperina basipalmata,
A. blumi, A. derongo, A. fryi (Australian),
A. gracilipes, A. novaebritanniae, A.
palmipes, A. pluvialis (Australian), A. rivularis,
A. robusta (Australian), and Liophryne
rhododactyla. The remaining eight have
toothlike irregularities along the edges of the
bones: Austrochaperina brevipes, Liophryne
allisoni, L. dentata, L. schlaginhaufeni, Oxydactyla
alpestris, O. coggeri, O. stenodactyla,
and Sphenophryne cornuta. In addition,
L. rubra apparently has tiny teeth.
The toothlike structures are not uniform
among species, but range from being relatively
large, almost fanglike, to fine serrations,
with the variation having no particular
correlation with the size of the frog. Some of
the finer structures (but not all) appear most
toothlike. Thus, it is likely that the various
structures are not homologous—some may
be true tooth vestiges (e.g., those of S. cornuta
and L. dentata), and others, especially
the grosser serrations in such species as A.
brevipes, may be neomorphs and not necessarily
homologous among species. Illustrations
in Wandolleck (1911: figs. 3, 12) contrast
the more toothlike structures of S. cornuta
with the serrations of L. schlaginhaufeni.
The question of the nature of the
toothlike structures is of consequence for determining
polarities, for if true (albeit vestigial)
teeth are present, this would represent
the plesiomorphic state, whereas the absence