Amphibian 621 225588189 2008-07-14T13:06:15Z Lindorm 1819888 Changed cladistic to phylogenetic, a more widely understood term {{Nofootnotes|date=July 2007}} {{otheruses}} {{taxobox | name=Amphibians or amphibia | fossil_range= [[Late Devonian|Late]] [[Devonian]] - Recent | image = Spea hammondii 1.jpg | image_width = 230px | image_caption = [[Spea hammondii|Western Spadefoot Toad]], ''Spea hammondii'' | regnum = [[Animal]]ia | phylum = [[Chordate|Chordata]] | subphylum = [[Craniata]] | superclassis = [[Tetrapod]]a | classis = '''Amphibia''' | classis_authority = [[Carolus Linnaeus|Linnaeus]], 1758 | subdivision_ranks = Subclasses and Orders | subdivision = &nbsp;&nbsp; Order [[Temnospondyli]] - ''extinct''<br/> Subclass [[Lepospondyli]] - ''extinct''<br/> Subclass [[Lissamphibia]]<br/> &nbsp;&nbsp; Order [[Anura]]<br/> &nbsp;&nbsp; Order [[Salamander|Caudata]]<br/> &nbsp;&nbsp; Order [[Caecilian|Gymnophiona]]}} {{see also|Prehistoric amphibian}} '''Amphibians''' (class Amphibia), such as frogs, toads, salamanders, newts, and gymnophiona, are cold-blooded animals that metamorphose from a juvenile, water-breathing form to an adult, air-breathing form. Typically, amphibians have four limbs. Unlike other land animals (amniotes), amphibians lay eggs in water, as their fish ancestors did. Amphibians are superficially similar to reptiles. Amphibian populations around the globe are threatened or extinct, and scientists do not agree on the reason. Amphibians evolved in the Devonian Period. They were a top predator in the Carboniferous Period, but proto-crocodiles evolved and took over that niche. ==Taxonomy== Traditionally, amphibians have included all [[tetrapod]]s that are not [[amniote]]s . They are divided into three [[Subclass (biology)|subclasses]], of which two are only known as extinct subclasses: * Subclass [[Labyrinthodontia]] (diverse Paleozoic and early Mesozoic group) * Subclass [[Lepospondyli]] (small Paleozoic group) * Subclass [[Lissamphibia]] (frogs, toads, salamanders, newts, etc.) Of these only the last subclass includes recent species. With the [[phylogenetic]] revolution, this classification has been modified, or changed, and the Labyrinthodontia discarded as being a [[paraphyletic]] group without unique defining features apart from [[plesiomorphy|shared primitive characteristics]]. Classification varies according to the preferred [[phylogeny]] of the author, and whether they use a [[Cladistic#Cladistic classification|stem-based or node-based]] classification. Generally amphibians are defined as the group that includes the common ancestors of all living amphibians (frogs, salamanders, etc) and all their descendants. This may also include extinct groups like the [[temnospondyli|temnospondyls]] (traditionally placed in the disbanded subclass "labyrinthodontia"), and the Lepospondyls. This means that there are a now large number of [[Basal (phylogenetics)|basal]] [[Devonian]] and [[Carboniferous]] [[tetrapod]] groups, described as "amphibians" in earlier books, that are no longer placed in the formal Amphibia. All recent amphibians are included in the subclass Lissamphibia, superorder Salientia, which is usually considered a [[clade]] (which means that it is thought that they evolved from a common ancestor apart from other extinct groups), although it has also been suggested also that salamanders arose separately from a temnospondyl-like ancestor (Carroll, 2007). Authorities also disagree on whether Salientia is a Superorder that includes the order Anura, or whether Anura is a sub-order of the order Salientia. Practical considerations seem to favour using the former arrangement now. The Lissamphibia, superorder Salientia, are traditionally divided into three [[Order (biology)|order]]s, but an extinct salamander-like family, the Albanerpetontidae, is now considered part of the Lissamphibia, besides the superorder Salientia. Furthermore, Salientia includes all three recent orders plus a single [[Triassic]] proto-frog, ''[[Triadobatrachus]]''. * Subclass [[Lissamphibia]] *** Family ''[[Albanerpetontidae]]'' - Jurassic to Miocene (extinct) ** Superorder ''[[Salientia]]'' *** Genus ''Triadobatrachus'' - Triassic (extinct) *** Order ''Anura'' ([[frog]]s and [[toad]]s): Jurassic to recent - 5,453 recent species in 45 families *** Order ''Caudata'' or ''Urodela'' ([[salamander]]s, [[newt]]s): Jurassic to recent - 560 recent species in 9 families *** Order ''Gymnophiona'' or ''Apoda'' ([[caecilian]]s): Jurassic to recent - 171 recent species in 3 families The actual number of species partly also depends on the taxonomic classification followed, the two most common classifications being the classification of the website AmphibiaWeb, University of California (Berkeley) and the classification by [[herpetologist]] Darrel Frost and The American Museum of Natural History, available as the online reference database Amphibian Species of the World (see external links below). The numbers of species cited above follow Frost. ==Systems== <!-- ===Circulatory=== frogs rock ===Respiratory=== ===Excretion=== ===Nervous=== --> ===Reproductive=== [[Image:Caecilian.jpg|226px|thumb|right|[[Caecilian]] from the [[San Antonio, Texas|San Antonio]] zoo]] For the purpose of [[Biological reproduction|reproduction]] most amphibians are bound to have [[fresh water]]. A few tolerate [[brackish water]], but there are no true [[seawater]] amphibians. Several hundred frog species in adaptive radiations (e.g., ''[[Eleutherodactylus]]'', the Pacific Platymantines, the Australo-Papuan microhylids, and many other tropical frogs), however, do not need any water whatsoever. They reproduce via direct development, an ecological and [[evolution]]ary adaptation that has allowed them to be completely independent from free-standing water. Almost all of these frogs live in wet [[Tropical and subtropical moist broadleaf forests|tropical rainforests]] and their eggs hatch directly into miniature versions of the adult, passing through the [[tadpole]] stage within the egg. Several species have also adapted to arid and semi-arid environments, but most of them still need water to lay their eggs. [[Symbiosis]] with single celled [[algae]] that lives in the jelly-like layer of the eggs has evolved several times. The larvae (tadpoles or polliwogs) breathe with exterior [[gill]]s. After hatching, they start to transform gradually into the adult's appearance. This process is called [[metamorphosis]]. Typically, the animals then leave the water and become terrestrial adults, but there are many interesting exceptions to this general way of reproduction. The most obvious part of the amphibian metamorphosis is the formation of four legs in order to support the body on land. But there are several other changes: * The gills are replaced by other [[Respiratory system|respiratory organ]]s, i.e., [[lung]]s. * The skin changes and develops [[gland]]s 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. ==Conservation== {{main|Decline in amphibian populations}} [[Image:Bufo periglenes1.jpg|thumb|right|300px|The [[Golden Toad]] of [[Monteverde]], [[Costa Rica]] was among the first casualties of amphibian declines. Formerly abundant, it was last seen in 1989.]] Dramatic declines in amphibian populations, including population crashes and mass localized [[extinction]], have been noted in the past two decades from locations all over the world, and amphibian declines are thus perceived as one of the most critical threats to global [[biodiversity]]. A number of causes are believed to be involved, including [[habitat destruction]] and modification, over-exploitation, [[pollution]], [[introduced species]], [[climate change]], destruction of the [[ozone layer]] (ultraviolet radiation has shown to be especially damaging to the skin, eyes, and eggs of amphibians), and diseases like [[chytridiomycosis]]. However, many of the causes of amphibian declines are still poorly understood, and are a topic of ongoing discussion. A global strategy to stem the crisis has been released in the form of the Amphibian Conservation Action Plan (available at www.amphibians.org). Developed by over 80 leading experts in the field, this call to action details what would be required to curtail amphibian declines and extinctions over the next 5 years - and how much this would cost. The Amphibian Specialist Group of the World Conservation Union (IUCN) is spearheading efforts to implement a comprehensive global strategy for amphibian conservation. On [[January 21]], [[2008]], Evolutionarily Distinct and Globally Endangered (EDGE), per chief Helen Meredith identified nature's most [[endangered]] [[species]]: "The EDGE [[amphibians]] are amongst the most remarkable and unusual species on the planet and yet an alarming 85% of the top 100 are receiving little or no conservation attention." The top 10 endangered species (in the [[List of endangered animal species]]) include: the [[Chinese giant salamander]], a distant relative of the [[newt]], the tiny [[Gardiner's Seychelles]], the limbless Sagalla caecilian, [[South Africa]]n [[ghost frogs]], lungless Mexican salamanders, the [[Malagasy]] rainbow [[frog]], Chile's Darwin frog ([[Rhinoderma rufum]]) and the Betic Midwife Toad.<ref>[http://www.reuters.com/article/latestCrisis/idUSL2038808 Reuters, Giant newt, tiny frog identified as most at risk]</ref><ref>[http://www.guardian.co.uk/environment/2008/jan/21/conservation guardian.co.uk, Drive to save weird and endangered amphibians]</ref><ref>[http://www.guardian.co.uk/environment/gallery/2008/jan/21/wildlife.conservation?picture=332110244 guardian.co.uk/environment, images of the species]</ref><ref>[http://www.guardian.co.uk/environment/gallery/2008/jan/21/wildlife.conservation guardian.co.uk/environment, Gallery: the world's strangest amphibians]</ref> ==Evolutionary history== The first major groups of amphibians developed in the [[Devonian Period]] from fish similar to the modern [[coelacanth]] where the fins had evolved into legs. These amphibians were around five meters long. The land was safe as the giant fish and sharks in the ocean could not come onto land. However, there were two problems with living out their entire lives on land. Primarily, the food that these amphibians consumed was in the water, but also at this point the skin on most of these amphibians was not water-tight. In the [[Carboniferous Period]], the amphibians moved up in the food chain and began to occupy the ecological position where we now find crocodiles. These amphibians were notable for eating the mega-insects on land and many types of fishes in the water. Towards the end of the [[Permian Period]] and the [[Triassic Period]], the amphibians started having competition with proto-crocodiles which led to their drop in size in the temperate zones or leaving for the poles. (Amphibians were able to hibernate during the winter whereas crocodiles could not, allowing the amphibians in higher latitudes protection from the reptiles.) Paleontologists once believed that the kind of lifestyle and adaptations that proto-amphibians was similar to the modern [[mudskipper]].{{Fact|date=July 2007}} (Mudskippers are not closely related to coelocanths.) {{Expand-section|date=May 2008}} == See also == *[[Chytridiomycosis]] *[[Fishapod]]s *[[Frog zoology]] *[[List of amphibians]] *[[Prehistoric amphibian]] *[[Sleep (non-human)|Sleep in nonhumans]] *[[Tetrapod]] ==References== {{reflist}} == Further reading == <div class="references-small"> *{{cite book | last = Carroll | first = Robert L. | title = Vertebrate Paleontology and Evolution | year = 1988 | publisher = W.H. Freeman & Co. | location = New York }} *{{cite book | last = Duellman | first = William E. | coauthors = Linda Trueb | title = Biology of Amphibians | year = 1994 | publisher = Johns Hopkins University Press | isbn = 978-0801847806 }} *{{cite journal | last = Frost | first = Darrel R. | title = The Amphibian Tree of Life | url = http://digitallibrary.amnh.org/dspace/handle/2246/5781 | journal = Bulletin of the American Museum of Natural History | volume = 297 | pages = 1–291 | year = 2006 | month = March | coauthors = Taran Grant, Julián Faivovich, Raoul H. Bain, Alexander Haas, Célio F.B. Haddad, Rafael O. De Sá, Alan Channing, Mark Wilkinson, Stephen C. Donnellan, Christopher J. Raxworthy, Jonathan A. Campbell, Boris L. Blotto, Paul Moler, Robert C. Drewes, Ronald A. Nussbaum, John D. Lynch, David M. Green, Ward C. Wheeler | doi = 10.1206/0003-0090(2006)297[0001:TATOL]2.0.CO;2 }} *{{cite journal | last = Pounds | first = J. Alan | title = Widespread amphibian extinctions from epidemic disease driven by global warming | url = http://www.nature.com/nature/journal/v439/n7073/full/nature04246.html | journal = Nature | volume = 439 | pages = 161–167 | year = 2006 | month = January | doi = 10.1038/nature04246 | coauthors = Martín R. Bustamante, Luis A. Coloma, Jamie A. Consuegra, Michael P. L. Fogden, Pru N. Foster, Enrique La Marca, Karen L. Masters, Andrés Merino-Viteri, Robert Puschendorf, Santiago R. Ron, G. Arturo Sánchez-Azofeifa, Christopher J. Still and Bruce E. Young }} *{{cite journal | last = San Mauro | first = Diego | coauthors = Miguel Vences, Marina Alcobendas, Rafael Zardoya and Axel Meyer | title = Initial diversification of living amphibians predated the breakup of Pangaea | url = | journal = American Naturalist | volume = 165 | pages = 590–599 | year = 2005 | month = May | doi = 10.1086/429523 }} *Solomon Berg Martin, ''Biology'' *{{cite journal | last = Stuart | first = Simon N. | coauthors = Janice S. Chanson, Neil A. Cox, Bruce E. Young, Ana S. L. Rodrigues, Debra L. Fischman, Robert W. Waller | title = Status and trends of amphibian declines and extinctions worldwide | url = http://www.sciencemag.org/cgi/content/full/306/5702/1783 | journal = Science | volume = 306 | issue = 5702 | pages = 1783–1786 | year = 2004 | month = December | doi = 10.1126/science.1103538 | pmid = 15486254 }} </div> == External links == {{Wikispecies|Amphibia}} {{Wikibookspar|Dichotomous Key|Amphibia}} * [http://www.amphibians.org/ Amphibian Specialist Group] * [http://www.amphibianark.org/ Amphibian Ark] * [http://research.amnh.org/herpetology/amphibia/index.html/ Amphibian Species of the World] The online database by Darrel Frost and The American Museum of Natural History * [http://www.amphibiaweb.org/ AmphibiaWeb] * [http://www.globalamphibians.org/ Global Amphibian Assessment] * [http://www.whose-tadpole.net/ Amphibians of central Europe] * [http://www.npwrc.usgs.gov/narcam/idguide/index.htm USGS--Online Guide for the Identification of Amphibians in North America north of Mexico] * [http://www.livingunderworld.org/ General amphibian biology information - Living UnderWorld] * [http://www.atlantabotanicalgarden.org/site/conservation/amphibian_research/ Atlanta Botanical Garden Amphibian Conservation Program] {{Chordata}} {{Amphibians}} [[Category:Amphibians| ]] {{Link FA|fi}} [[af:Amfibie]] [[ar:برمائيات]] [[bn:উভচর প্রাণী]] [[zh-min-nan:Lióng-chhe-lūi]] [[bs:Vodozemci]] [[bg:Земноводни]] [[ca:Amfibi]] [[cs:Obojživelníci]] [[cy:Amffibiad]] [[da:Padde]] [[de:Amphibien]] [[et:Kahepaiksed]] [[el:Αμφίβια]] [[es:Amphibia]] [[eo:Amfibioj]] [[eu:Anfibio]] [[fa:دوزیستان]] [[fr:Amphibia]] [[ga:Amfaibiach]] [[gd:Dà-bheathach]] [[gl:Anfibio]] [[ko:양서류]] [[hr:Vodozemci]] [[io:Amfibia]] [[id:Amfibia]] [[is:Froskdýr]] [[it:Amphibia]] [[he:דו-חיים]] [[jv:Amfibi]] [[pam:Amphibian]] [[ka:ამფიბიები]] [[la:Amphibia]] [[lv:Abinieki]] [[lb:Lurchen]] [[lt:Varliagyviai]] [[li:Amfibieë]] [[jbo:banfi]] [[hu:Kétéltűek]] [[mk:Водоземец]] [[ml:ഉഭയജീവി]] [[ms:Amfibia]] [[nl:Amfibieën]] [[ja:両生類]] [[no:Amfibier]] [[nn:Amfibium]] [[oc:Amphibia]] [[nds:Amphibien]] [[pl:Płazy]] [[pt:Anfíbios]] [[ro:Amfibian]] [[rm:Amphibia]] [[qu:Allpa yaku kawsaq]] [[ru:Земноводные]] [[scn:Anfibbiu]] [[simple:Amphibian]] [[sk:Obojživelníky]] [[sl:Dvoživke]] [[sr:Водоземци]] [[sh:Vodozemac]] [[stq:Amphibien]] [[su:Ampibi]] [[fi:Sammakkoeläimet]] [[sv:Groddjur]] [[ta:நிலநீர் வாழிகள்]] [[te:ఉభయచరము]] [[th:สัตว์สะเทินน้ำสะเทินบก]] [[to:Monumanu nofo ʻuta mo vai]] [[tr:İki yaşamlılar]] [[uk:Земноводні]] [[ur:جل تھلیل]] [[wa:Glumiantès biesses]] [[zea:Amfibieën]] [[zh:两栖动物]]