By Heather Heying
This diverse group of tree frogs is in a constant state of redefinition, and it is unlikely that the groups included here represent the family's final configuration. As defined here, there are three subfamilies, containing roughly 12 genera, and more than 300 species. Rhacophorids are found throughout much of the old world tropics. Several genera occur in the Asian tropics, from India and Sri Lanka to Japan, including the islands of SE Asia. One genus is restricted to tropical Africa, and four genera, including the subfamily Mantellinae, are endemic to Madagascar.
Rhacophorids are small to large frogs (15 - 120 mm snout-vent length) bearing several arboreal adaptations, including cartilaginous intercalary elements between the terminal and penultimate phalanges, and toe discs. They have flattened bodies, with broad, flat skulls. Synapomorphies of the group include only one slip of the extensor digitorum communis longus muscle, inserting on the distal portion of fourth metatarsal; and the outermost slip of the palmaris longus muscle inserting on the proximolateral rim of the aponeurosis palmaris. If hyperoliids are not sister to rhacophorids, synapomorphies also include a frontoparietal trapezoidal, and bifurcate terminal phalanx. Like related groups, rhacophorids 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. Pupils are horizontal. Amplexus is axillary, and tadpoles, when present, are usually type IV. Diploid number is 24 or 26.
Along with the hyperoliids, rhacophorids are the treefrogs of the Old World, analogous to hylids in tropical America. Rhacophorids exhibit a diversity of forms and habits. In Madagascar, where frogs are speciose and diverse, the rhacophorids represent the largest anuran group. There, Boophis tends to be arboreal, but Aglyptodactylus and the mantellines inhabit terrestrial niches. One notable exception is Mantella laevigata, whose arboreal adaptations, skin toxins, bright color, and complex courtship and parental behaviors suggest convergence with the neotropical dendrobatids. In addition, several mantellines breed in treeholes. The African Chiromantis builds arboreal foam nests, which may be, in part, made of seminal fluid. Multiple males have been observed amplexing a single female, while all participants whip up the foam with their legs. Some Asian species lay eggs in treeholes, and have a shortened, nonfeeding larval stage. Other species (Philautus) lay arboreal eggs that undergo direct development. Rhacophorus nigromaculatus, the "flying frog," uses extensive webbing and a flattened body to parachute from tree to tree.
Rhacophorids are Neobatrachians, but relationships among the families of these "advanced" frogs are almost wholly unresolved. Within the Neobatrachia, rhacophorids are members of the superfamily Ranoidea. Family relationships among the ranoids are in a state of chaos, and should be considered unknown. The rhacophorids and hyperoliids were originally placed in a single family, Polypedatidae. Since then, each has been accorded family status, but genera are sometimes swapped between the two groups. The subfamily Mantellinae has been moved back and forth between Rhacophoridae and Ranidae multiple times (and the rhacophorids have been considered ranids by at least one author). One hypothesis suggests a sister relationship between the Mantellines and Hyperoliidae, which would render both traditional placements for the Mantellinae inaccurate. Some authors posit that hyperoliids and rhacophorids were both derived independently from separate groups of ranids. Recent work suggests that the Madagascan rhacophorids (including mantellines) are sister to the monophyletic clade of Asian and African rhacophorids (Richards, et al. 2000).
No fossil rhacophorids are known.
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Contributors
Heather Heying (author).
