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Amphibian facts for kids

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Amphibian
Temporal range: late Devonian – Recent
Frogs (top left), Seymouria (fossil) (top right), salamanders and newts (bottom left) and caecilians (bottom right)
are all amphibians.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Amphibia

Amphibians are animals that live on land and in water. 'Amphibian' comes from two Greek words: "amphi" and "bio". Amphi means "both". Bio means "life". 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 hatching they are tadpoles which live in the water and have gills. The tadpoles change into adults in a process called metamorphosis. When they are adults, 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.

For quite a while, during the Carboniferous and early Permian, amphibia were top predators on land, especially in the low-lying tropical river systems. In the drier conditions which followed, they were less effective, and the ancestors of mammals and reptiles (the Synapsids and Sauropsids) gradually took over the land.

They laid cleidoic eggs, which had hard shells, and could be laid out of water. Most of the large, early, amphibians went extinct in the Triassic period; a few survived to the Lower Cretaceous. Some amphibians, such 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.

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 world-wide, except Antarctica, though restricted in distribution by their need for moist or watery habitats to reproduce. 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 declining all over the world. Conservation is therefore an important concern.

Litoria xanthomera amplexus
Male and female orange-thighed frog
Axolotl in COEX Aquarium
Axolotl
Australia green tree frog (Litoria caerulea) crop
Australia green tree frog

Description

American Toad singing
American toad, (Anaxyrus americanus) singing

Amphibians like to live near freshwater in warm weather. There have also been species which live in forests, deserts and arctic conditions. Adult amphibians use lungs, and they also get oxygen through their skin, so long as it is moist.

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

Alternatively, many other amphibia have toxic skin, which is harmful to predators. These are poisonous to eat. This is an important defense against predation. Connected to this is the use of warning coloration. They may be in vivid colors of red, black, and yellow.

Poison Dart Frog (Dendrobates azureus)
Poison Dart Frog (Dendrobates azureus)

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.

Amphibians have color 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.

Anura

Bufo speciosus
This Texas toad 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.

Teichfrosch
Frogs such as this have smooth (soft) wet skin

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. Their 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.

Caudata

Feuer Salamander 2
This fire salamander has yellow and black stripes along its body: typical warning colouration

The order Caudata is the salamanders.

Newts are salamanders which spend their life in the water even though they are adults. They are classified in the subfamily Pleurodelinae of the family Salamandridae. The California newt can survive a fire by spreading its mucous over its body.

Respiration differs between species of salamanders. Species that lack lungs respire through gills. In most cases, these are external gills, visible as tufts on either side of the head. Many species, such as the Olm, have both lungs and gills as adults.

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.

Chinese Fire Bellied Newts 2
Chinese fire-bellied newts has red stripes on their front body, which they can raise when attacked. This is also warning coloration

Axolotls, from the genus Ambystoma (or mole salamanders), are neotenic amphibians. This means they reach maturity and reproduce while still in a larval form.

Most salamanders and newts have some defence against predators, usually a poison which makes them uneatable. Their bright colors are a warning coloration. If, instead, they are camouflaged, this means they are probably not protected by a toxin.

The second line of defense is to shed their tail, which can grow again. The tail wriggles a bit, attracts the predator while salamander moves off.

Gymnophiona

Beddome's Caecilian
Beddome's Caecilian, 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.

They are burrowing amphibians, though some are aquatic, this means that they dig themselves in wet soil like worms. Their heads are strong and have bones that help them dig. Because caecilians have a lot of vertebrae, they can bend easily.

Caecilians are found in tropical Africa, Asia and Central and South America. There are 171 different species.

Reproduction

Ghatophryne rubigina
Kerala stream toad Ghatophryne rubigina is a species of toad

Amphibians are the only vertebrates to go through metamorphosis. This means that their young look different from their adult. Amphibians usually reproduce in early spring to late summer, though some reproduce in winter and fall.

Most frogs and toads, such as the common frog (Rana temporalis), gather in large groups to ponds, rivers, swamps and lakes to breed. Male frogs and toads may croak to attract a female.

Frogs can lay up to 100 to 60,000 eggs in one clutch. This is called "frogspawn".

Amphibia's reproduction is one way or another, tied to water, this is because their eggs, although covered by jelly, cannot survive long in dry conditions.

Frogspawn closeup
Frogs eggs are called "frogspawn"
Tadpole 1
Tadpole 3
Tadpole 4
Tadpole 6

Most female amphibians lays her eggs in water. The eggs are laid one by one or in batches. Batches of eggs can look like a long chain or a ball of foam. They may wrap their eggs around plants in the water. They do this so their eggs will not drift away.

Tree frogs usually lay their eggs on a leaf in a rainwater pool. Bullfrogs, such as the male American bullfrog and the male African bullfrog, stay with their tadpoles and protect them from predators.

They also move their tadpoles by using their nose to dig a channel to another place where there is more water. They do this so their tadpoles do not dry up.

Most amphibians leave their eggs to look after themselves. Fish and other animals eat most of their eggs. Male midwife toads carry their eggs on their backs. When they are ready to hatch, the toad goes back to the water and release them.

Tadpoles

Tadpoles do not have lungs when they hatch and instead have gills. Because gills have a large surface area, tadpoles can get more oxygen by using them. Young tadpoles have their gills exposed. When they get older, their gills are covered over by skin. When they hatch, tadpoles eat constantly. The tadpoles eat what is left of their eggs, this is usually their first food.

Frog, toad and newt tadpoles eat plants such as algae and pondweed or filter feed. When they get older, they may start to feed on tiny animals in the water. Salamander tadpoles and surinam horned toad tadpoles are carnivorous throughout their tadpole stage.

The eggs of the spadefoot toad hatches in three days. Their tadpoles complete their metamorphosis in six to eight days. The reason for this is because spadefoot toads lay their eggs in places where water will dry up soon.

Tadpoles of frogs and toads start to grow their back legs first. They then grow front legs a few weeks later. When tadpoles grow their limbs they are called "froglets". This is because they look rather like a smaller version of adult frogs and toads. Their tails continue to get shorter until there is nothing left of them.

Habitats

Salamanders and newts can be found living in streams. Salamanders can be found in rotten logs, holes or underground places that are wet such as under leaves. Web-toed salamanders live in habitats where there are a lot of rocks. They like to hide under rocks and stones.

The tailed frogs, like to live in cold water habitats. In their habitat, amphibians like to live where there are a lot of places to hide. These include nearby small trees, logs and plants. While underwater they like to hide near aquatic plants and rocks. Tree and dart frogs like to live in forests on trees, plants and on the ground under leaves.

Some amphibia can be found living in the desert or the arctic. The desert froglet lives in the desert. They are only active at night, when temperatures are much cooler. It rarely rains in the desert and because of this, desert frogs will burrow to keep cool.

Wood frog (44091409341)
Wood frog

They use their mucus to keep them wet. The mucus will harden to keep the water it produces from escaping. Once it has done this, it will stay in its cocoon and will not move. They will stay like this for several months to years until a rainstorm.

The spadefoot toad will spit on the ground. Once they have done this, they will lay on it. Their bodies will take in the water. Their bodies are thin and have a lot of blood vessels, this helps them to be able to take water through their skin.

RanaArvalisBlueMale3
Moor frog - the males turn blue during mating season

Arctic frogs such as the wood frog, moor frog and the common frog have to live with freezing temperatures for a long time. They will burrow in places where they can get into a cocoon. Like every living organisms, amphibians must have water to survive.

Amphibians however, need freshwater. Some frogs such as burrowing frogs can keep water in their bladders. This allows them to stay underground without drying up.

Diet

Cambodia Frog Eating Frog
Amphibians are predatory animals. If there is no food to be found, they will eat each other

Amphibians are predatory animals. 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.

Many amphibians use their sticky tongues to catch their prey. They will 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 will eat almost anything they can fit into their mouths. These include rodents, birds, ducklings, small fish and small mammals.

Crab-eating Frog (Fejervarya cancrivora) (14136245104)
Crab-eating Frog

Most frogs are cannibalistic, and will eat each other if food is no where to be found. Some amphibians will even eat their own tadpoles and eggs if there is no food for them.

In captivity, pet frogs will be given crickets, worms, small fish, rodents and fruit flies.

Adult amphibians can help decrease the mosquito population by eating most of their larvae.

Conservation

Bufo periglenes1
The golden toad of Monteverde, Costa Rica was last seen in 1989

The amphibian population have been decreasing from all locations in the world. Scientists have said that the declining of amphibians is one of the most critical threats to global biodiversity.

A number of causes are believed to be involved. These include habitat destruction, over-exploitation, pollution, introduced species, climate change, destruction of the ozone layer, and diseases like chytridiomycosis.

Ultraviolet radiation damages the skin, eyes and eggs of amphibians.

Human use

Supermarktfrosch
Bullfrogs being sold alive at a supermarket in China
Swikee Kodok Oh with Rice
Swikee Kodok Oh - Chinese frog leg dish

Bullfrog legs are a source of food for Southern United States and the Midwestern United States. In the state of California, people must have a license to catch bullfrogs for food. People hunt bullfrogs at night near rivers. The bullfrogs' legs are cooked, while their backs are fried.

In China, bullfrogs are sold alive for eating. However, they are later cooked dead with vegetables. The emperor newt is hunted in China for food. They are also used there for medicine.

In schools, bullfrogs are dissected in biology classes. Usually, this is done in grammar school.

Amphibians are also kept as pets. They are kept in aquariums or a terrarium.

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