The true frogs, family Ranidae, have the widest distribution of any frog family. They are abundant throughout most of the world, occurring on most continents except Antarctica. The true frogs are present in North America, northern South America, Europe, Asia, Madagascar, Africa, and from the East Indies to New Guinea; the species native to Australia—the Australian Wood Frog (Hylarana daemelii)—is restricted to the far north.
Typically, true frogs are smooth, moist-skinned frogs, with large, powerful legs and extensively webbed feet. The true frogs vary greatly in size, ranging from small—such as the Wood Frog (Rana sylvatica)—to the largest frog in the world, the Goliath frog (Conraua goliath).
Many of the true frogs are aquatic or live close to water. Most species lay their eggs in the water and go through a tadpole stage. However, as with most families of frogs, there is large variation of habitat within the family. Those of the genus Tomopterna are burrowing frogs native to Africa and exhibit most of the characteristics common to burrowing frogs around the world. There are also arboreal species of true frogs, and the family includes some of the very few amphibians that can live in brackish water.
Systematics
The subdivisions of the Ranidae are still a matter of dispute, although many are coming to an agreement. Most authors believe the subfamilyPetropedetinae is actually a distinct family called Petropedetidae.The validity of the Cacosterninae is likewise disputed; they are usually merged in the Petropedetinae but when the latter are considered a distinct family the Cacosterninae are often awarded at least subspecific distinctness too, and sometimes split off entirely. Still, there is general agreement today that the Mantellidae, which were formerly considered another ranid subfamily, form a distinct family. There is also a recent trend to split off the forked-tongued frogs as distinct family Dicroglossidae again.
In addition, the delimitation and validity of several genera is in need of more research (though much progress has been made in the last years). Namely how the huge genus Rana is best split up requires some more study. While the splitting-off of several genera—like Pelophylax—is rather uncontroversial, the American bullfrogs formerly separated in Lithobates and groups like Babina or Nidirana represent far more disputed cases.
While too little of the vast diversity of true frogs has been subject to recent studies to say something definite, as of mid-2008 studies are ongoing and several lineages are recognizable.
Genera like Nyctibatrachus, Staurois, and the complex around Euphlyctis, Hoplobatrachus, Nannophrys, Sphaerotheca and the paraphyleticFejervarya are probably very ancient offshoots of the main Raninae lineage.
Amolops has been generally delimited as a monophyletic group.
Odorrana and Rana plus some proposed minor genera (which probably ought to be included in the latter) form another group.
A group including Clinotarsus, Huia in the strict sense and Meristogenys
An ill-defined assemblage of Babina, Glandirana, Hylarana, Pulchrana, Sanguirana, Sylvirana, as well as Hydrophylax and Pelophylax which are probably not monophyletic. Most of them are now treated as junior synonyms of the genus Hylarana.
