Hemisotidae

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This tiny family of burrowing frogs that exhibit remarkable parental care is comprised of a single genus, which contains eight species. The family name is thus synonymous with the genus, Hemisus, and also with an incorrect form rarely used today, Hemisidae. Hemisotids are restricted to tropical and subtropical sub-Saharan Africa.

Shovel-nosed frogs are smooth-skinned and small, with short, stout forelimbs and small heads with pointy snouts. Synapomorphies of this group include a skull that is highly modified for burrowing, and the lack of a sternum (also observed in Rhinophrynus and Brachycephalidae). Hemisus also has a vertical pupil, fused carpals and tarsals, and a notched tongue. Hemisotids have eight holochordal, procoelous presacral vertebrae, an ossified sternum and omosternum, palatines but no parahyoid, and an astragalus and calcaneum that are fused only at the ends. Shovel-nosed frogs have no teeth. Amplexus is axillary. Aquatic type IV tadpoles have beaks, denticles, and a sinistral spiracle. Diploid number is 24.

Hemisotids are unlike almost all other frogs in that they burrow head first, a behavior made possible by their extremely ossified skulls. They live in savannah and scrub forests, are primarily fossorial, and specialize in eating ants and mites. Hemisus females dig underground breeding chambers while in amplexus, into which they lay a small number of relatively large eggs. The male leaves this chamber after fertilizing the eggs, while the female attends the (terrestrial) eggs and young tadpoles (tadpoles can apparently remain outside of water for several days). Several conflicting observations and pseudo-observations have been put forth to explain what happens next (see van Dijk 1985 and 1997, and Kaminsky et al 1999). One or more of the following four behaviors takes place as the tadpoles begin to hatch. The mother may 1) dig an underground tunnel to the surface, which the tadpoles follow her down, finally exiting into ephemeral surface ponds; 2) carry tadpoles and almost-hatched eggs to the surface on her back; 3) passively await seasonal flooding, which washes her tadpoles away into surface pools, and/or 4) build a "slide" on the muddy surface, which allows tadpoles easy entry into pools. Hemisus clearly exhibits an elaborate form of extended maternal care, though its precise manifestation is still in some dispute.

Hemisotids are unambiguously Neobatrachians, but relationships among the families of these "advanced" frogs are almost wholly unresolved. Within the Neobatrachia, hemisotids are members of the superfamily Ranoidea, a clade of derived forms that likely loses its monophyly if Dendrobatidae is included. Family relationships among the ranoids are in a state of chaos, and should be considered unknown. Some researchers continue to regard Hemisus as a subfamily (Hemisinae) within Ranidae, rendering the family Hemisotidae unnecessary. Some characters (e.g. vertical pupils) suggest a relationship to the Hyperoliidae. Two other previously ranid subfamilies (now Arthroleptidae) also share characters with both ranids and hyperoliids. At the current time, we have no idea who the hemisotids are related to.

No fossil hemisotids are known.

Cannatella, D., L. Ford, and L. Bockstanz. 1996. Neobatrachia: Tree of Life. (Website.) http://tolweb.org/tree?group=Neobatrachia&contgroup=Salientia

Cogger, H. G., and R. G. Zweifel, editors. 1998. Encyclopedia of Reptiles and Amphibians, 2nd edition. Academic Press, San Diego.

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.

Kaminsky, S. K., K. E. Linsenmair, and T. U. Grafe. 1999. Reproductive timing, nest construction and tadpole guidance in the African pig-nosed frog, Hemisus marmoratus. Journal of Herpetology 33:119-123.

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.

van Dijk, D. E. 1985. Hemisus marmoratum adults reported to carry tadpoles. South African Journal of Science 81:209-210.

van Dijk, D. E. 1997. Parental care in Hemisus (Anura: Hemisotidae). South African Journal of Zoology 32:56-57.

Zug, G. R. 1993. Herpetology: an introductory biology of amphibians and reptiles. Academic Press, San Diego.

Contributors

Heather Heying (author).

Glossary

bilateral symmetry

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

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

metamorphosis

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

having the capacity to move from one place to another.