By Heather Heying
This diverse family of more than 100 species is assigned to 20 extant genera, in two subfamilies. The common name for myobatrachids underscores the fact that these are the dominant terrestrial frogs of Australia, filling niches that are elsewhere occupied by bufonids, leptodactylids, microhylids, pelobatids, and ranids. All genera are found in Australia, and only a few occur anywhere else. Three genera are also known from Papua New Guinea; four from Tasmania.
The Australian frogs are split almost evenly into two subfamilies, each of which have several distinct characters. Across both subfamilies, these frogs lack ribs, have eight amphicoelous presacral vertebrae with persistent notochords in juveniles, completely fused astragalus and calcaneum, and inguinal amplexus. Most myobatrachids have teeth on the upper jaw (some genera lack teeth altogether), and a cartilaginous omosternum and sternum. Adult sizes of Myobatrachines are typically 20 -40 mm snout-vent length, but species in a few genera grow to 80 mm; Limnodynastines are larger, ranging from 35 - 115 mm. Diploid number is usually 24, although some Limnodynastes have 22.
The myobatrachids exhibit a wide range of lifestyles, but there are no treefrogs among their ranks. Many are found in arid deserts, where they spend most of their lives underground, burrowing through sand with the help of a digging spade on each hind foot (e.g. Heleioporus, Neobatrachus). Species of Notaden also burrow, but are distinguished in having poorly ossified skulls, being brightly colored, and secreting sticky white toxins. Some fossorial species burrow head first (Myobatrachus). Other species are found in marshes (Limnodynastes, Crinia), along mountain streams (Taudactylus), or in the streams themselves (Rheobatrachus). Some species have aquatic, feeding, type IV tadpoles. Megistolotis tadpoles are adapted for torrents. The females of some species make foam nests for their young, in open water, burrows, or even on land (e.g. Kyarranus). Terrestrial eggs undergo direct development in Arenophryne and Myobatrachus. In several species, elaborate parental care has evolved. Nonfeeding tadpoles develop in the inguinal brood pouches of male Assa. Eggs and tadpoles of Rheobatrachus develop in the stomach of the mother. Both species of these "gastric-brooding frogs" may now be extinct, perhaps early victims of an epidemic disease spreading among Australian anurans in the early 1980s.
Myobatrachids are placed in the Neobatrachia, but relationships among the families of these "advanced" frogs is controversial at best. Most authors identify a superfamily, alternately called Bufonoidea or Hyloidea, which includes all the neobatrachians that are not Ranoids or Microhyloids. The group Bufonoidea is thus sketchy at best. Within Bufonoidea, myobatrachids may be related to the Sooglossidae, a small family restricted to the Seychelles. Some authors have found that no characters unite the two myobatrachid subfamilies and indeed, that Myobatrachinae appears to be closely related to the sooglossids (and perhaps ranids), whereas Limnodynastinae seems more closely related to the leptodactylids. If this is true, Myobatrachidae is a paraphyletic group. Other work has suggested that the myobatrachids are sister to the rest of Bufonoidea. To complicate matters further, the genus Rheobatrachus has often been considered a separate lineage.
Fossils of extant genera are known from the Miocene and Pleistocene of Australia. Additionally, an extinct genus, Indobatrachus, from the Eocene, has been tentatively assigned to the Myobatrachidae. This placement raises biogeographical questions, as Indobatrachus was found in India.
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http://tolweb.org/tree?group=Myobatrachinae&contgroup=Neobatrachia
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Contributors
Heather Heying (author).
