Encyclopedia of Life

Amphibians

Amphibians are cold-blooded animals thatmetamorphose from a young, water-breathing

form to an adult, air-breathing form. Amphibians include such animals as frogs, newts, salamanders, toads, and caecilians. Early amphibians were the first animals to leave the sea and venture onto land, forming a crucial

link from fish to terrestrial reptiles.

Amphibians include all tetrapods that are not amniotes, and are divided into three subclasses; Labyrinthodontia, Lepospondyli, and Lissamphibia. Two of the three subclasses (Labyrinthodontia and Lepospondyli) are known only as extinct.

Scientific classification

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Superclass:Tetrapoda

Class: Amphibia

The distribution of amphibians is worldwide, except in Antarctica and Greenland. They are found on landmasses and in fresh water. Frogs are the most widespread, occurring on all major landmasses inhabited by amphibians. They live in a great variety of habitats, ranging from deserts to rain forests, permanent ponds to high mountain meadows.

Voice production is

largely an attribute of frogs. Salamanders and caecilians produce noises (coughs, and grunts), but not for communication. Frogs have complex sound production and perception systems, with species-specific warning, defensive, and breeding communications.

Mode of locomotion varies greatly among amphibians. From limbless caecilians using their heads like shovels to burrow into the ground, to salamanders and caecilians using body muscle contraction to propel through the water. On land, the limbs give considerable propulsion to the body. Frogs make use of their long hind-limbs to effect several kinds of locomotion; jumping, hopping, swimming, burrowing, and climbing.

Unlike other land animals (amniotes), amphibians lay eggs in the water. After hatching, the young gradually start to transform into their adult appearance, a process called metamorphosis.

Several changes take place during the metamorphosis, the most obvious being the formation of four legs, in order to support itself on lands. Others changes include:

* The gills are replaced by other respiratory organs, i.e., lungs.

* The skin changes and develops glands to avoid dehydration.

* The eyes develop eyelids and adapt to vision outside the water.

* An eardrum is developed to lock the middle ear.

* In frogs and toads, the tail disappears.

Amphibians are ecological indicators and in the past few decades there has been observed a dramatic decline in populations of amphibians around the world.

A number of causes are believed to be involved in this population decline, including habitat destruction and modification, over-exploitation, pollution, introduced species, climate change,pollutants, and disease.

A global strategy to stem the crisis has been released in the form of the Amphibian Conservation Action Plan.

Please visit www.amphibians.org for more information.

Works Cited http://animals.nationalgeographic.com/

animals/amphibians.html

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Please enjoy this short film I created at http://animals.nationalgeographic.com/animals/article/filmmaker.html

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