Amphibian

*, typical of the large-size early amphibians 310–295 million years ago]]

**Amphibians** are members of the class **Amphibia**. The living ones are frogs (including toads), salamanders (including newts) and caecilians. They are four-legged vertebrates which are cold blooded.

Amphibians lay their eggs in water, usually in a foam nest. After  they are tadpoles, which live in the water and have gills. The tadpoles change into adults in a process called metamorphosis.  When they are adult, they have lungs to breathe instead of gills, and legs. Adult amphibians also use their skin to take in oxygen, and some species of salamanders do not have lungs.

The earliest amphibians evolved in the Devonian from lobe-finned fish which had jointed leg-like fins with digits. They could crawl along the sea bottom. Some had developed primitive lungs to help them breathe air when the stagnant pools of the Devonian swamps were low in oxygen. They could also use their strong fins to hoist themselves out of the water and onto dry land if necessary.

The only living amphibiana today are the Lissamphibia. These include the Anura (frogs and toads), Caudata (salamanders and newts) and Gymnophiona (caecilians). They are all rather small, compared with mammals or reptiles. The smallest frog and vertebrate in the world is the New Guinea frog (*Paedophryne amauensis*). The biggest amphibian is the Chinese giant salamander (*Andrias davidianus'').

Amphibia are found everywhere in the world, except Antarctica, and there are about 5,565 different species: 88% of them are in the Anura. In number of species, they are more successful than mammals, though they occupy a smaller range of habitats. However, it is said that amphibian populations have been  all over the world.

#### Defences 
Amphibians may be camouflaged in brown and green, and if so they are prey for birds and reptiles. Their colour gives them camouflage, which is their main defence.

Alternatively, many other amphibia have toxic skin, which is  to predators. These are poisonous to eat. This is an important defence against predation. Connected to this is the use of warning colouration. They may be in vivid colours of red, black, and yellow. Research into the rough-skinned newt and the garter snake shows this is a typical case of co-evolution. Where they live in the same area, the newts get more poisonous, and the snakes develop more resistance to the poison.

#### Sight 
Amphibians have colour vision and depth of focus for clear sight. They also have eyelids, glands and ducts which keep the eyes moist. These are adaptations to life on land: amphibia were the first vertebrates to have these features.

### Development 
Some amphibia, such as the frog known as the common coquí, lay eggs out of water (in this case, on palm leaves). The eggs develop directly into adult frogs, by-passing the tadpole stage. Others, like mudpuppies and olms, have a different development. In a process called neoteny, they become sexually developed as tadpoles with gills. They continue to live in the water.

## Anura 
 has smooth (soft) wet skin]]
 has rough (hard) dry skin]]

The order Anura includes the frogs and toads. There is no fundamental difference between frogs and toads. Frogs have a short body, webbed digits (fingers or toes), protruding eyes, forked tongue and no tail. They are exceptional jumpers: many of their features, particularly their long, powerful legs, are adaptations to improve jumping performance. They often live in semi-aquatic or inhabit humid areas.

A popular distinction is often made between frogs and toads on the basis of their appearance. Toads' warty skin is an adaptation for making their toxic slime. Apart from these glands, their skin is dry, and that is an adaptation to drier habitats. These features have evolved a number of times independently: convergent evolution. The distinction has no taxonomic basis. The only family exclusively given the common name "toad" is Bufonidae (the "true toads"), but many species from other families are commonly called "toads".

Some terrestrial species lack both lungs and gills and perform gas exchange through their skin. Even some species with lungs also respire through the skin in this manner.

The skin of salamanders secretes mucus. This helps to keep the animal moist when on dry land, keeps their salt balance while in water, and lubricates during swimming. Salamanders also secrete poison from glands in their skin, and some additionally have skin glands for secreting courtship pheromones.p182 If touched, slender salamanders will  on the ground and then run away.

## Gymnophiona 
, like all other caecilians, do not have feet or limbs.]]

The order Gymnophiona includes the caecilians. These are long, cylindrical, limbless animals that look like snakes or worms. Their skin has circular folds, increasing their similarity to the segments of earthworms. Some are aquatic, but most live underground in burrows they hollow out. Many caecilians give birth to live young. In species which lay eggs, the eggs may undergo metamorphosis before they hatch. Caecilians are found in tropical Africa, Asia and Central and South America. There are 171 different species.

Their skins make a mucus that makes them slippery enough to slip through the earth.  They can make a toxic material in their skins, as many frogs and toads do.

## Reproduction 
'' mating]]

Amphibians are the only vertebrates to go through metamorphosis. This means that their young look different from their adult.p8 Amphibians usually reproduce in early spring to late summer, though some reproduce in winter and fall. Sometimes, males fight to mate with a female. They get toxins from what they eat. They eat insects in their habitat. These insects get the poison from a plant. The toxin has been discovered in beetles.  Caecilian eyes are small and dark. Most of them are blind. Most amphibians have a good sense of smell, even underwater.

The skeletal system of amphibians are similar to other four-legged animals. They have a spine, rib cage, long bones such as the humerus and femur. They also have short bones such as the phalanges, metacarpals, and metatarsals. Most amphibians have four limbs, except for caecilians. The bones in amphibians are  and do not weigh much.

## Diet 
Amphibia are predators. They mostly eat live invertebrates and animals that do not move too quickly. These include caterpillars, earthworms, crayfish, water beetles, snails and dragon fly larvae.p667 Many amphibians use their sticky tongues to catch their prey. They swallow the animal whole, but may chew it just a bit for it to go down their throats. The Ranidae family and the Ceratophrys genus eat almost anything they can fit into their mouths. Most frogs are cannibalistic, and may eat each other if food is nowhere to be found. Some amphibians may even eat their own tadpoles and eggs if there is no food for them. 
 
### Feeding in captivity 
In captivity, pet frogs will be given crickets, worms, small fish, rodents and fruit flies. Adult amphibians can help  the mosquito population by eating most of their larvae.

Caecilians eat earthworms, termites and beetle larvae, and also small lizards.p31 Caecilians rely on their smell to find food. They like to eat earthworms and will find them by picking up their chemical signals. Salamanders and newts are fed a lot of different types of worms. These include blood worms and earthworms. They can eat small fish such as goldfish, fathead minnows and guppies. Salamanders also eat crickets and pinkies, which are baby rats. Scientists have said that the declining of amphibians is one of the most  threats to global biodiversity.

The Amphibian Conservation Action Plan (ACAP) have released a global strategy to help the amphibian population. It was developed by over 80 leading experts. The Amphibian Specialist Group of the World Conservation Union (IUCN) are working on another global strategy to help amphibian populations.

On January 21, 2008, Evolutionarily Distinct and Globally Endangered (EDGE) released a statement to the public. It was created by Helen Meredith, who identified nature's most endangered species. Meredith explains that 85% of the top 100 endangered amphibians list are receiving little or no conservation attention.

## Human use 
### As food 
Bullfrog legs are a source of food for Southern United States and the Midwestern United States. People hunt bullfrogs at night near rivers. The bullfrogs' legs are cooked, while their backs are fried.p9 In China, bullfrogs are sold alive for eating. However, they are later cooked dead with vegetables. In the state of California, people must have a license to catch bullfrogs for food.p256 In schools, bullfrogs are dissected in biology classes. Usually, this is done in grammar school.p85 The dissecting is a method for teaching students the anatomy of a bullfrog.p4 They are kept in aquariums or a terrarium. A terrarium is a tank that is  with plants and soil on one side. On the other side, there is water. Most amphibians would need one place for land and another for water.p7 Water for amphibia needs dechlorination. The chlorine in tap water can kill amphibia. Some amphibians popular exotic pets, and are found in pet stores that sell reptiles.p22

## Related pages
*List of amphibians
*Frogs as pets

## References 
## Reference books 
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## Other websites 
* Amphibian Specialist Group
* AmphibiaWebEcuador 
* Amphibian Ark
* AmphibiaWeb
* EDGE
* Global Amphibian Assessment 
* USGS—Online Guide for the Identification of Amphibians in North America north of Mexico
* General amphibian biology information—Living UnderWorld
* Panama Amphibian Rescue and Conservation Project
* Atlanta Botanical Garden Amphibian Conservation Program
* Froglife (British conservation charity)
* A guide to Amphibians