By Heather Heying
This family of often arboreal, brightly colored frogs contains 14 genera, in more than 220 species. Most authors split the hyperoliids into three subfamilies. Twelve of the fourteen genera are endemic to sub-Saharan Africa. The remaining two, Tachycnemis and Heterixalus, are endemic to the Seychelles and Madagascar, respectively.
Hyperoliids are small to medium sized frogs (15 - 80 mm snout-vent length) bearing several arboreal adaptations, including cartilaginous intercalary elements between the terminal and penultimate phalanges, and toe discs. Several synapomorphies have been reported for hyperoliids, but many of these may actually diagnose a larger group. The lack of fusion of the second distal carpal and tarsal elements is sometimes considered paedomorphic, and is not shared by any ranids (though perhaps by Mantellines). Other characters known from hyperoliids include the presence of a dentomentalis muscle, the absence of a nuptial pad, claw-shaped terminal phalanges, vertical pupils, and a cartilaginous sternum. Like related groups, hyperoliids lack ribs, have eight holochordal-procoelous presacral vertebrae, have dentate upper jaws, have palatines but no parahyoid, and an astragalus and calcaneum that are fused only at their ends. Amplexus is axillary, and young develop indirectly (with the possible exception of Chrysobatrachus) into type IV tadpoles. Many species have smooth, brightly patterned skin that almost looks enameled. Diploid number is 22, 24, or 30.
Along with the rhacophorids, hyperoliids are the treefrogs of the Old World, analogous to hylids in tropical America. Like hylids, hyperoliids exhibit a diversity of forms and habits. Many are arboreal, but some are terrestrial, including several Kassina species that locomote by walking or running rather than hopping. The type genus, Hyperolius, which represents more than half the species known in this family, contains several species that deposit eggs on vegetation above water. In Afrixalus, the leaf-folding frog, mating pairs construct an over-water leaf nest by folding leaves together with their legs, and gluing them together with oviducal secretions. Acanthixalus lays eggs in treeholes, Opisthothylax has arboreal foam nests, and Leptopelis lays terrestrial eggs (hatching tadpoles find their way to ponds). Madagascan Heterixalus are often found calling at night from rice fields. Diet varies widely as well, with some notable examples including Tornierella, who specialize on snails, and Afrixalus fornasinii, the only terrestrial frog known to prey on eggs of other species of anurans.
Hyperoliids are Neobatrachians, but relationships among the families of these "advanced" frogs are almost wholly unresolved. Within the Neobatrachia, hyperoliids 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, but certainly not all, authors consider the Hyperoliidae to be a monophyletic group. Several genera are sometimes swapped between Hyperoliidae and Rhacophoridae; the original placement of these two families within a single group, Polypedatidae, points to decades of confusion on this issue. Hypotheses of sister relationship have included hyperoliids with the Mantellinae (a Madagascan subfamily usually placed in Rhacophoridae or Ranidae), and hyperoliids with the rhacophorids (including Mantellines). An additional hypothesis posits that hyperoliids and rhacophorids were both derived independently from separate groups of ranids.
No fossil hyperoliids are known.
Cannatella, D. 1996. Hyperoliidae: Tree of Life. (Website.) 
http://tolweb.org/tree?group=Hyperoliidae&contgroup=Neobatrachia
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.
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.
Stebbins, R. C., and N. W. Cohen. 1995. A natural history of amphibians. Princeton University Press, Princeton.
Zug, G. R. 1993. Herpetology: an introductory biology of amphibians and reptiles. Academic Press, San Diego.
Contributors
Heather Heying (author).
