Amphibians lay their eggs in water, usually in afoamnest. Afterhatching they aretadpoles, which live in the water and havegills. The tadpoles change into adults in a process calledmetamorphosis. When they are adult, they havelungs to breathe instead of gills, and legs. Adult amphibians also use their skin to take inoxygen, and somespecies of salamanders do not have lungs.
The earliest amphibiansevolved in theDevonian fromlobe-finnedfish 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 Devonianswamps were low inoxygen. They could also use their strong fins to hoist themselves out of the water and onto dry land if necessary.[1][2]
For tens of millions of years, during theCarboniferous and earlyPermian, amphibia weretop predators on land, especially in the low-lying tropical river systems. In drier conditions, they were less effective, and the ancestors of mammals and reptiles (theSynapsids andSauropsids) gradually took over the land. They laidcleidoic eggs, which had hard shells, and could be laid out of water. Most of the early large amphibians wentextinct in theTriassic period; a few survived to theLower Cretaceous.[2]
The only living amphibiana today are theLissamphibia. These include theAnura (frogs and toads),Caudata (salamanders and newts) andGymnophiona (caecilians). They are all rather small, compared with mammals or reptiles. The smallest frog and vertebrate in the world is theNew Guinea frog (Paedophryne amauensis). The biggest amphibian is theChinese giant salamander (Andrias davidianus).
Amphibia are found everywhere in the world, exceptAntarctica, and there are about 5,565 different species: 88% of them are in theAnura.[3] In number of species, they are more successful thanmammals, though they occupy a smaller range ofhabitats. However, it is said that amphibian populations have beendeclining all over the world.[4] Conservation is therefore an important concern.
Amphibians like to live nearfreshwater in warm weather. There have also been species which live inforests,deserts andarctic conditions. Adult amphibians use lungs, and they also get oxygen through their skin, so long as it ismoist.[5]
Amphibians may becamouflaged in brown and green, and if so they areprey for birds and reptiles. Their colour gives themcamouflage, which is their main defence.
Alternatively, many other amphibia havetoxic skin, which isharmful to predators. These arepoisonous to eat. This is an importantdefence against predation. Connected to this is the use ofwarning colouration. They may be in vivid colours of red, black, and yellow. Research into therough-skinned newt and thegarter snake shows this is a typical case ofco-evolution. Where they live in the same area, the newts get more poisonous, and the snakes develop more resistance to the poison.[6][7][8]
Amphibians havecolour vision and depth of focus for clear sight. They also have eyelids, glands and ducts which keep the eyes moist. These areadaptations to life on land: amphibia were the first vertebrates to have these features.
Some amphibia, such as the frog known as thecommon 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, likemudpuppies andolms, have a different development. In a process calledneoteny, they become sexually developed as tadpoles with gills. They continue to live in the water.
Frogs such as thisedible frog has smooth (soft) wet skinThisTexas toad has rough (hard) dry skin
Theorder 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.[9]
A popular distinction is often made between frogs and toads on the basis of their appearance. Toads' warty skin is anadaptation for making theirtoxicslime. 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" isBufonidae (the "true toads"), but many species from other families are commonly called "toads".[9]
Newts are salamanders which spend their life in the water even though they are adults. They are classified in thesubfamily Pleurodelinae of the familySalamandridae.
Respiration differs between species of salamanders. Species that lack lungs respire throughgills. In most cases, these are external gills, visible as tufts on either side of the head. Some salamanders that are terrestrial havelungs that are used in respiration, although these are simple and sac-like, unlike the more complex organs found inmammals. Many species, such as theOlm, have both lungs and gills as adults.[10]
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 secretesmucus. This helps to keep the animal moist when on dry land, keeps their salt balance while in water, and lubricates during swimming. Salamanders also secretepoison from glands in their skin, and some additionally have skin glands for secreting courtshippheromones.[10]
Axolotls, from the genusAmbystoma (or mole salamanders), areneotenic amphibians. This means they get to sexual maturity and reproduce while still in alarval form.
Most salamanders and newts have somedefence against predators, usually a poison which makes them uneatable. Their bright colours arewarning colouration. If, instead, they arecamouflaged, this means they are probably not protected by atoxin.
The second line of defence is to shed their tail, which can grow again. The tail wriggles a bit, attracts the predator while the business part of the salamander moves off.
There are over 350lungless salamanders. Most of them are terrestrial and are active in daytime. Lungless salamanders may communicate with their nose.[11]p168Slender salamanders are found in thePacific Coast. They are sometimes called "worm salamanders". This is because they have slimmer (skinny) bodies than most salamanders.[11]p182 If touched, slender salamanders willbounce on the ground and then run away.
The orderGymnophiona includes the caecilians.[12] These are long, cylindrical, limbless animals that look likesnakes orworms. 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.[13][14]
Amphibians are the only vertebrates to go throughmetamorphosis. This means that their young look different from their adult.[15]p8 Amphibians usually reproduce in early spring to late summer, though some reproduce in winter and fall.[11]p156 Most frogs and toads, such as thecommon frog (Rana temporalis), gather in large groups to ponds, rivers, swamps and lakes to breed.[15]p10 Male frogs and toads maycroak to attract a female. When a female frog has chosen a mate, the male frog hops on top of her. They swim together as she lay eggs in the water.[16] Sometimes, males fight to mate with a female.[16]p7 Frogs can lay up to 100 to 60,000 eggs in oneclutch. This is called "frogspawn".
It is a fundamental feature of amphibia that their reproduction is, one way or another, tied to water. This is because their eggs, although covered by jelly, cannot survive long in dry conditions.
Frogs eggs are called "frogspawn"Some amphibians lay eggs that are very clear. This makes it easy to watch a tadpole grow inside its egg
Most female amphibians lays her eggs in water. Males releasesperm tofertilize them. The eggs are laid one by one or inbatches. Batches of eggs can look like a longchain or a ball of foam. They maywrap their eggs around plants in the water. They do this so their eggs will notdrift away.[15]p8
Tree frogs usually lay their eggs on aleaf in a rainwater pool. Bullfrogs, such as the maleAmerican 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 achannel to another place where there is more water.[15]p9 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. Malemidwife toads carry their eggs on their backs. When they are ready to hatch, the toad goes back to the water and release them.[16]p10
Thisorange-thighed Frog tadpole has only a head and a tail. It will grow back legs and front hands in a couple of weeks. It will then lose its tail and become a young frog.
Tadpoles do not have lungs when they hatch and instead havegills. Because gills have a largesurface area, tadpoles can get more oxygen by using them. Young tadpoles have their gillsexposed. When they get older, their gills are covered over by skin.[15]p6 When they hatch, tadpoles eat constantly. The tadpoles eat what is left of their eggs, this is usually their first food.[15]p8
Frog, toad and newt tadpoles eatplants such asalgae andpondweed orfilter feed. When they get older, they may start to feed on tiny animals in the water. Salamander tadpoles andsurinam horned toad tadpoles arecarnivorous throughout their tadpole stage.[15]p9 Surinam horned toad tadpoles are veryaggressive. They eat other tadpoles if food is nowhere to be found. The eggs of the spadefoot toad hatches in three days. Their tadpoles complete their metamorphosis in six to eight days. This is because spadefoot toads lay their eggs in places where water will dry up soon.[15]p13
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. Tadpoles will also start to grow a backbone after growing their front limbs. After this, their mouths get bigger and their eyes will stick out more. After a tadpole has grown its hands, their tails continue to get shorter until there is nothing left of them.[15]p11
Most frogs like to spend their time in the water hiding near aquatic plantsThisAlpine newt isbasking on a rock. It does this to get heat from the sun
Salamanders and newts can be found living instreams. Salamanders can be found inrotten logs, holes or underground places that are wet such as under leaves.[11]p152 Web-toed salamanders live in habitats where there are a lot of rocks. They like to hide under rocks and stones.[11]p195 The tailed frogs, like to live in cold water habitats.[11]p199 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 thedesert or thearctic.[15]p12 Thedesert 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 willburrow to keep cool. They use their mucus to keep them wet. They will spread it all over their bodies. The mucus will harden to keep the water it produces from escaping. Once the desert frog has done this, it will stay in itscocoon and will not move. They will stay like this for several months to years until a rainstorm. Desert frogs and toads lose water more quickly. The spadefoot toad willspit 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 ofblood vessels, this helps them to be able to take water through their skin. TheCalifornia newt can survive afire by spreading its mucous over its body.[15]p12
Arctic frogs such as thewood frog,moor frog and the common frog has 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 cankeep water in theirbladders. This allows them to stay underground without drying up. Thecrab-eating frog lives near water that is somewhatsalty. They will eatsaltwater crabs. Torrent salamanders lives in cold waters. Because of this they have shorter lungs. Short lungs helps them to float easily.
This poison dart frog's skin is blue. This color warns animals that they are toxicMost amphibians have a good sense of smell. Their eyes have color and clear vision
Many amphibia have secretions in their skin which makes them toxic. They do not produce toxins themselves.[17] 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.[17] This means that they are likely the cause of poisons found in amphibians. Amphibians do not produce batrachotoxin in captivity, which means that it is not harmful to touch them. TheAmerican Indian tribecomechingóns used the toxins of thearrow dart frogs whenhunting.[17]
Newts in the genusTaricha has a poison calledtetrodotoxin, aneurotoxin. Scientists believe that toxins in newts are caused bybacteria in the generaPseudoalteromonas,Pseudomonas andVibrio. Because of this, the newts do not have a lot of predators. However, some species of snakes have develop aresistance. This means that they can eat newts without the toxin hurting them. It is a case ofco-evolution.
Amphibians' eyes havelids,glands andducts. They have good colour vision[18] Caecilian eyes are small and dark. Most of them areblind. Most amphibians have a good sense ofsmell, even underwater.
Theskeletal system of amphibians are similar to other four-legged animals. They have aspine,rib cage, long bones such as thehumerus andfemur. They also have short bones such as thephalanges,metacarpals, andmetatarsals. Most amphibians have four limbs, except for caecilians. The bones in amphibians arehollow and do not weigh much.[19]
Amphibians are predatory animals. If there is no food to be found, they will eat each other.
Amphibia arepredators. They mostly eat liveinvertebrates and animals that do not move too quickly. These includecaterpillars, earthworms,crayfish,water beetles,snails anddragon fly larvae.[20]p667 Many amphibians use their sticky tongues to catch theirprey. They swallow the animal whole, but may chew it just a bit for it to go down their throats. TheRanidae family and theCeratophrys genus eat almost anything they can fit into their mouths.[20]p668 These includerodents,birds,ducklings, smallfish and small mammals.[21] Most frogs arecannibalistic, 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.[22]
Caecilians eat earthworms,termites and beetle larvae, and also smalllizards.[25]p31 Caecilians rely on their smell to find food. They like to eatearthworms and will find them by picking up theirchemical signals. Salamanders and newts are fed a lot of different types of worms. These includeblood worms and earthworms. They can eat small fish such asgoldfish,fathead minnows andguppies. Salamanders also eat crickets andpinkies, which are baby rats.[20]p771
The amphibian population have been decreasing from all locations in the world.[4] Scientists have said that the declining of amphibians is one of the mostcritical threats to globalbiodiversity.[4] A number of causes are believed to be involved. These includehabitat destruction,over-exploitation,pollution, introduced species,climate change, destruction of theozone layer, and diseases likechytridiomycosis.Ultraviolet radiation damages the skin, eyes and eggs of amphibians. However, the declines of amphibian population are still not understood.[26]
The Amphibian Conservation Action Plan (ACAP) have released aglobal strategy to help the amphibian population. It was developed by over 80 leading experts.[27] TheAmphibian Specialist Group of the World Conservation Union (IUCN) are working on another global strategy to help amphibian populations.[27] TheAmphibian Ark (AA) is anorganization that was created to help the public be aware of the decline in amphibian populations. They have been working withzoos andaquaria around the world. They try to encourage them to create a natural habitat for threatened amphibians.[27] Another project is the Panama Amphibian Rescue and Conservation Project (PARCP) which are trying to spread awareness about chyridiomycosis. The disease is spreading into easternPanama and threatening all amphibians living there.[28]
On January 21, 2008, Evolutionarily Distinct and Globally Endangered (EDGE) released a statement to the public.[29] 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.
Bullfrogs being sold alive at a supermarket in China.
Bullfrog legs are a source of food for Southern United States and the Midwestern United States.[30] People hunt bullfrogs at night near rivers. The bullfrogs' legs are cooked, while their backs arefried.[31]p9 In China, bullfrogs are sold alive for eating. However, they are later cooked dead withvegetables. In the state of California, people must have a license to catch bullfrogs for food.[32]p256 In schools, bullfrogs aredissected inbiology classes. Usually, this is done ingrammar school.[33]p85 The dissecting is amethod for teaching students theanatomy of a bullfrog.[33]p85 Theemperor newt is hunted in China for food. They are also used there for medicine. Burrowing frogs are able to hold water in their bladder, because of thisindigenous Australians use them to drink water.[15]p13
Amphibians are also kept as pets.[34]p4 They are kept inaquariums or a terrarium. A terrarium is a tank that isdecorated with plants andsoil on one side. On the other side, there is water. Most amphibians would need one place for land and another for water.[34]p8 Each type of amphibian should have its special needs taken care of. Semi-aquatic amphibians need both land and water divided in the tank. Tropical frogs would needmist and highhumidity in their terrariums.[35]p7 Water for amphibia needsdechlorination. Thechlorine in tap water can kill amphibia. Some amphibians popularexotic pets, and are found inpet stores that sell reptiles.[34]p22
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↑2.02.1Carroll, Robert 2009.The rise of amphibians: 365 million years of evolution. Baltimore: The Johns Hopkins University Press.ISBN978-0-8018-9140-3
↑Pough F.H.; et al. (2003).Herpetology. 3rd ed, Benjamin Cummings.ISBN0131008498.
↑Geffeney, Shana L. | display-authors = etal 2005. Evolutionary diversification of TTX-resistant sodium channels in a predator-prey interaction.Nature434: 759–763.
↑9.09.1Zweifel, Richard G; Cogger H.G. & Zweifel R.G. 1998.Encyclopedia of reptiles and amphibians. San Diego: Academic Press. pp. 91–92.ISBN0-12-178560-2
↑10.010.1Cogger, Harold G. ed 1998.Encyclopedia of reptiles and amphibians. San Diego: Academic Press.ISBN0-12-178560-2.
↑ Nussbaum, Ronald A; Cogger H.G. & Zweifel R.G. eds 1998.Encyclopedia of reptiles and amphibians. San Diego: Academic Press. pp. 52–59.ISBN 0-12-178560-2
↑Duellman, William E.; Zug, George R. (2012)."Amphibian".Encyclopædia Britannica. Retrieved2012-03-27.{{cite encyclopedia}}: CS1 maint: multiple names: authors list (link)
↑Maglia A.M.; et al. (2007)."AmphibAnat".The amphibian anatomical ontology web project. Archived fromthe original on 2012-01-16. Retrieved2012-03-25.
↑20.020.120.2Wells, Kentwood David 2007. The ecology & behavior of amphibians. University of Chicago Press,ISBN0226893340
↑The illustrated encyclopedia of North American reptiles and amphibians: an essential guide to reptiles and amphibians of USA, Canada, and Mexico, MobileReference, 2008,ISBN978-1-60501-459-3
↑Gray, Susan 2009.Bullfrog (animal invaders). Cherry Lake Publications.ISBN978-1-60279-327-9
↑Storer, Malcolm 2004.Experimental approaches to conservation biology. University of California Press.ISBN978-0-520-24024-7
