SooglossidaeSeychelle Frogs
This tiny family of geographically restricted frogs has confounded all systematists who have attempted to discern its relationship to other anurans. With only three species in two genera, this family is restricted to two small islands (Silhouette and MahÉ) in the Seychelles, an island group roughly 250 miles North of Madagascar in the Indian Ocean
Seychelle frogs are small (40 mm snout-vent length) and terrestrial, with digits that terminate in small, pointed discs. The only known synapomorphy of this group is the presence of a sesamoid bone in the heel region. Several other characters have been used to unite the sooglossids with either the myobatrachids or the ranoid frogs. Sooglossids, along with ranoids, have a semitendinosus tendon that passes dorsal to the m. gracilis, and partial fusion of the epicoracoid cartilages and sternum of the pectoral girdle. Like myobatrachines, sooglossids have a ventrally incomplete cricoid ring, horizontal pupils, winglike alary processes on the hyoid, and a divided sphenethmoid. Amplexus is inguinal. Diploid number is 26.
Sooglossids live in mossy forests on the granitic islands of the Seychelles. Along with the caecilians, these comprise the oldest herpetofauna on the Seychelles, an island group that has attracted much attention from biogeographers and systematists alike. Two distinct reproductive modes are known from seychelle frogs. Both Sooglossus species lay terrestrial eggs, which the females guard until hatching. Sooglossus gardinera eggs hatch directly into froglets after three to four weeks. Sooglossus sechellensis eggs, by contrast, hatch in two to three weeks into nonfeeding tadpoles that lack mouthparts and spiracles. These tadpoles crawl onto the mother's back, where they remain until they metamorphose. The reproductive mode of the third species, Sooglossus thomasseti, is not known, although the large eggs are suggestive of direct development. Males call not in choruses, but individually, though adults of both sexes appear to lack tympana (eardrums).
Sooglossids are unambiguously placed in the Neobatrachia, but beyond that, nothing about their evolutionary relationships are resolved. Most authors identify a superfamily, alternately called Bufonoidea or Hyloidea, which includes all the neobatrachians that are not Ranoids or Microhyloids. Sooglossids have often been proposed to be related to the myobatrachids, in the Bufonoidea, on the basis of several morphological characters, as well as karyotype and amplectic position. In particular, sooglossids may be sister to the subfamily Myobatrachinae, the other subfamily of myobatrachids being more distantly related to both groups. Alternately, some authors have hypothesized that the sooglossids are not Bufonoids at all, but members of the Ranoidea. This relationship is supported by soft tissue characters, and the biogeography of the families involved. Finally, recent molecular work suggested an unresolved trichotomy between sooglossids, ranoids, and all other neobatrachians. It seems that the sooglossids will not be well understood phylogenetically any time soon.
No fossil sooglossids are known.
Cannatella, D. 1996. Sooglossidae: Tree of Life. (Website.)
Duellman, W. E., and L. Trueb. 1986. Biology of Amphibians. Johns Hopkins University Press, Baltimore, MD.
Ford, L. S., and D. Cannatella. 1993. The major clades of frogs. Herpetological Monographs 7:94-117.
Hay, J. M., I. Ruvinsky, S. B. Hedges, and L. R. Maxson. 1995. Phylogenetic relationships of amphibian families inferred from DNA sequences of mitochondrial 12s and 16s ribosomal RNA genes. Molecular Biology and Evolution 12:928-937.
Nussbaum, R. A. 1982. Heterotopic bones in the hindlimbs of frogs of the families Pipidae, Ranidae, and Sooglossidae. Herpetologica 38:312-320.
Pough, F. H., R. M. Andrews, J. E. Cadle, M. L. Crump, A. H. Savitzky, and K. D. Wells. 1998. Herpetology. Prentice-Hall, Inc., Upper Saddle River, NJ.
Zug, G. R. 1993. Herpetology: an introductory biology of amphibians and reptiles. Academic Press, San Diego.
Contributors
Heather Heying (author).
Glossary
- bilateral symmetry
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having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- ectothermic
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animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- metamorphosis
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A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
- motile
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having the capacity to move from one place to another.