Frogs and Toads.The members of this group, the largest of the living orders of amphibians, have loosely fitting skins, no tails when adult, bony pectoral girdles, and usually no ribs. Fertilisation is always external, and no species remains larval for life. The anatomy is specialised for jumping: the vertabral column is short, with extensively fused vertebrae, the main bones of the limbs are fused, and the hind limbs are much longer than the forelimbs. Frogs and toads breathe by moving the floor of the mouth, first drawing air into the mouth and then forcing it into the lungs after closing the nostrils. There are twelve families.
Ascaphids: 4 species
Members of this family have ribs and rudimentary tail-wagging muscles. There are two genera, one in New Zealand and one in North America.
Pipid toads: 15species
These toads are entirely aquatic. Only the larvae have ribs. Both jaws are usually toothless. and all species are tongueless . Eyelids are sometimes present.
Discoglossids: 10 species
Discoglossids, found in Europe and Asia, have toothless lower jaws, and their ribs are present throughout life.
There is one species
Mexican burrowing toad, Rhinophrynus dorsalis: found among scrub and savanna on the coastal plains of Mexico and Guatemala.
Pelobatids: 54 species
These small toads with minute teeth are found in Eurasia, North Africa and North America
Toads: 300 species
The toads in this family have no upper teeth. There are several genera, the best known being Bufo, which contains 250 species and is found on all continents except Australia. These toads live on land and are active at dusk and before dawn. They are specialised for crawling and trap insects on their sticky tongues.
Atelopodids: 26 species
There are only two genera in this family of small, brightly coloured frogs, which live near forest streams in Central and South America. Many species walk rather than hop. In one species, Atelopus stelzneri the tadpoles hatch within 24 hours of the eggs being laid.
Tree frogs: almost 600 species
Treefrogs are adapted for life in trees, and have extra cartilage between the two end digits of the hands and feet, which gives them a better grip. The family, which also contains ground-living and aquatic forms, includes the large genus Hyla, containing 350 species, which is found throughout the world, except in Africa south of the Sahara and in eastern Polynesia.
Leptodactylids: 650 species
Members of this family are found in South and Central America, Australia and southern Africa. Several genera are adapted to the more arid areas of Australia. Duringthe dry season they retire deep into the ground. Some species lay their eggs in burrows and rely on rainfall for development; the tadpoles' metamorphosis is so rapid that they become adults before the water evaporates.
Frogs: hundreds of species
This group, which occurs on all continents, is unspecialised except for jumping - the specialisation common to all anurans. It includes the virtually world wide genus Rana, containing 200-300 species, all of which have a notch on the end of the tongue. Some, such as the marsh frog Rana ridibunda and the edible frog Rana esculenta, are aquatic and have vocal sacs at the corner of the mouth; others have no vocal sacs.
Oar-legged frogs: hundreds of species
These frogs, found in the tropics of Africa, Madagascar and eastern Asia , resemble tree frogs in their adaptations to living in trees. They have webbed hind feet.
Microhylids: hundreds of species
This little-known family of burrowing and tree living forms is found in the Old and New World tropics, except western africa. The tadpoles hatch either at an advanced stage or completely metamorphosed.
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