SPHENOPHRYNE - American Museum of Natural History

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102 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 253 Fig. 58. SEM photograph of palatal folds of Liophryne rhododactyla BPBM 9793, anterior to top of figure. Scale line spans 2 mm. FRONTOPARIETALS: In most species these are somewhat parallel-sided bones, flaring posteriorly and in some with lateral margins converging slightly anteriorly (figs. 66–68). Exceptions are A. blumi, A. gracilipes, and A. novaebritanniae, in which the lateral margins diverge gradually before flaring (see Zweifel, 1985b: fig. 45, for gracilipes). There is considerable interspecific variation in the width of the braincase relative to the width of the skull, with the ratio ranging from 0.209 to 0.455. Two small species, A. gracilipes (0.429) and A. novaebritanniae (0.444), and Sphenophryne cornuta (mean 0.376 [0.336–0.455], N 3) have the widest braincases. The frontoparietal region is unusually short in cornuta where the ratio of braincase length to skull length averages 0.559 (0.526–0.580, N 3). The lowest such ratio in all other specimens is 0.631 in one of five Oxydactyla stenodactyla. PREMAXILLAE: The premaxillae of 15 species are illustrated in figures 63 and 64, where ventral views emphasize the shape of the premaxillary shelf. Interspecific variation in the shelf involves its length (relative to the width of the bone) and the degree of emargination of the posterior edge. The relatively longest bones are seen in O. alpestris and O. stenodactyla, with O. coggeri approaching these two in length. The first two also show the least emargination. Inasmuch as these (and coggeri) are secretive species and probably are head-first burrowers in litter and grass clumps, the relatively robust bones may serve a strengthening function. Another variable in premaxillae is the extent to which the ascending process slopes forward. In species with snouts that project notably beyond the lip, such as A. palmipes and A. rivularis, the ascending process is conspicuous in ventral view, whereas processes that are essentially vertical cannot be seen (O. alpestris, O. coggeri). The variation shown in the drawings should not be taken Fig. 59. SEM photographs, enlarged views of conical projections of posterior palatal fold shown in fig. 58. Left scale line spans 100 m, right 20 m.
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
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SPHENOPHRYNE - American Museum of Natural History

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