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'{{Automatic taxobox | name = Vertebrates | fossil_range = [[Cambrian]]-Recent,<ref name = "Shu et al. 1999"/> {{fossil range|525|0}} | image = Vertebrates.png | image_width = 220 px | image_caption = Individual organisms from each major vertebrate group. Clockwise, starting from top left: [[Fire Salamander]], [[Saltwater Crocodile]], [[Southern Cassowary]], [[Rhynchocyon petersi|Black-and-rufous Giant Elephant Shrew]], [[Ocean Sunfish]] | taxon = Vertebrata | authority = [[Georges Cuvier|Cuvier]], 1812 | subdivision_ranks = Simplified grouping (see text) | subdivision = *[[Fish]]es *[[Tetrapod]]s }} '''Vertebrates''' {{IPAc-en|ˈ|v|ɜr|t|ɨ|b|r|ə|t|s}} are [[animal]]s that are members of the [[subphylum]] '''Vertebrata''' {{IPAc-en|-|ɑː}} ([[chordates]] with [[Vertebra|backbone]]s and [[Vertebral column|spinal column]]s). Vertebrates include the overwhelming majority of the [[phylum]] [[Chordata]], with currently about 64,000 [[species]] described.<ref>{{cite web |url=http://data.iucn.org/dbtw-wpd/html/Red%20List%202004/completed/table2.1.html | title=A Global Species Assessment | publisher=World Conservation Union |author=Jonathan E.M. Baillie, et al. |year=2004}}</ref> Vertebrates include the [[Agnatha|jawless fish]], [[bony fish]], [[shark]]s and [[Batoidea|rays]], [[amphibian]]s, [[reptiles]], [[mammals]], and [[birds]]. [[Extant taxon|Extant]] vertebrates range in size from the [[frog]] species ''[[Paedophryne amauensis]]'', at as little as 7.7&nbsp;mm (0.3&nbsp;inch), to the [[blue whale]], at up to 33&nbsp;m (110&nbsp;ft). Vertebrates make up about 4% of all described animal species; the rest are [[invertebrates]], which lack backbones. The vertebrates traditionally include the [[hagfish]], which do not have proper vertebrae, though their closest living relatives, the [[lamprey]]s, do have vertebrae.<ref name=hagfish>{{cite journal|title=Monophyly of Lampreys and Hagfishes Supported by Nuclear DNA–Coded Genes | author=Kuraku et al. |date=December 1999|journal=Journal of Molecular Evolution | volume = 49 | pages = 729–35|doi=10.1007/PL00006595|pmid=10594174|last2=Hoshiyama|first2=D|last3=Katoh|first3=K|last4=Suga|first4=H|last5=Miyata|first5=T|issue=6}}</ref> Hagfish do, however, possess a [[cranium]]. For this reason, the vertebrate subphylum is sometimes referred to as "[[Craniata]]" when discussing morphology. Molecular analysis since 1992 has suggested that the hagfish are most closely related to lampreys,<ref>{{cite journal|last=Stock|first=David|coauthors=Whitt GS|title=Evidence from 18S ribosomal RNA sequences that lampreys and hagfish form a natural group|journal=Science|date=7|year=1992|month=August|volume=257|issue=5071|doi=10.1126/science.1496398|url=http://www.sciencemag.org/content/257/5071/787.short|accessdate=22 November 2011|pages=787–9|pmid=1496398|bibcode = 1992Sci...257..787S }}</ref> and so also are vertebrates in a [[monophyletic]] sense. Others consider them a sister group of vertebrates in the common taxon of Craniata.<ref>{{cite journal|last=Nicholls|first=Henry|title=Mouth to Mouth|date=10 September 2009|journal=Nature|volume=461|issue=7261|pages=164–166|doi=10.1038/461164a|pmid=19741680}}</ref> == Etymology == The word ''vertebrate'' derives from the Latin word ''vertebratus'' ([[Natural History (Pliny)|Pliny]]), meaning ''joint of the spine''.<ref>{{cite web | title=vertebrate |publisher=Dictionary.com. |work=Online Etymology Dictionary |author=Douglas Harper, Historian |url=http://dictionary.reference.com/browse/vertebrate}}</ref> It is closely related to the word ''[[vertebra]]'', which refers to any of the bones or segments of the spinal column.<ref>{{cite web | title=vertebra |publisher=Dictionary.com. |work=Online Etymology Dictionary |author=Douglas Harper, Historian |url=http://dictionary.reference.com/browse/vertebra}}</ref> == Anatomy and morphology == {{see also|Mammal anatomy|Fish anatomy}} All vertebrates are built along the basic chordate [[body plan]]: a stiff rod running through the length of the animal ([[vertebral column]] or [[notochord]]),<ref>{{cite web|last=Waggoner|first=Ben|title=Vertebrates: More on Morphology|url=http://www.ucmp.berkeley.edu/vertebrates/vertmm.html|publisher=UCMP|accessdate=13 July 2011}}</ref> with a hollow tube of nervous tissue (the [[spinal cord]]) above it and the [[gastrointestinal tract]] below. In all vertebrates, the mouth is found at, or right below, the anterior end of the animal, while the [[anus]] opens to the exterior before the end of the body. The remaining part of the body continuing aft of the anus forms a [[tail]] with vertebrae and spinal cord, but no gut.<ref name=Romer>Romer, A.S. (1949): ''The Vertebrate Body.'' W.B. Saunders, Philadelphia. (2nd ed. 1955; 3rd ed. 1962; 4th ed. 1970)</ref> ===Vertebral column=== The defining characteristic of a vertebrate is the [[vertebral column]], in which the [[notochord]] (a stiff rod of uniform composition) found in all [[Chordata|chordates]] has been replaced by a segmented series of stiffer elements (vertebrae) separated by mobile joints (intervertebral discs, derived embryonically and evolutionarily from the notochord). However, a few vertebrates have secondarily lost this anatomy, retaining the notochord into adulthood, such as the [[sturgeon]]<ref>{{cite book|title=Functional anatomy of the vertebrates: an evolutionary perspective|year=2001|publisher=Harcourt College Publishers|isbn=978-0-03-022369-3|author=Liem, Karel F.|coauthors=Warren Franklin Walker|page=277}}</ref> and the ''[[Latimeria]]''. [[Gnathostomata|Jawed vertebrates]] are typified by paired appendages (fins or legs, which may be secondarily lost), but this is not part of the definition of vertebrates as a whole. [[Image:Naturkundemuseum Berlin - Dinosaurierhalle.jpg|800px|thumb|centre|Fossilized skeleton of ''[[Diplodocus carnegii]]'', showing an extreme example of the [[Vertebral column|backbone]] that characterizes the vertebrates. Exhibited at the [[Museum für Naturkunde]] (''Museum of Natural Science''), Berlin.]] ===Gills=== [[File:Gills (esox).jpg|thumb|right|Gill arches bearing gills in a [[northern pike|pike]]]] All [[Basal (phylogenetics)|basal]] vertebrates breathe with [[gills]]. The gills are carried right behind the head, bordering the posterior margins of a series of openings from the [[esophagus]] to the exterior. Each gill is supported by a cartilagenous or bony [[gill arch]].<ref>{{cite book|last=Scott|first=Thomas|title=Concise encyclopedia biology|year=1996|publisher=Walter de Gruyter|isbn=978-3-11-010661-9|page=542}}</ref> The [[bony fish]] have three pairs of arches, [[cartilaginous fish]] have five to seven pairs, while the primitive [[jawless fish]] have seven. The vertebrate ancestor no doubt had more arches, as some of their [[Chordata|chordate]] relatives have more than 50 pairs of gills.<ref name="Romer" /> In [[amphibians]] and some primitive bony fishes, the [[larva]]e bear external gills, branching off from the gill arches.<ref>{{cite journal|journal=The American Naturalist|year=1957|volume=91|page=287|publisher=Essex Institute}}</ref> These are reduced in adulthood, their function taken over by the gills proper in fishes and by [[lung]]s in most amphibians. Some amphibans retain the external larval gills in adulthood, the complex internal gill system as seen in fish apparently being irrevocably lost very early in the evolution of [[tetrapod]]s.<ref name=Gaining_ground>Clack, J. A. (2002): Gaining ground: the origin and evolution of tetrapods. ''Indiana University Press'', Bloomington, Indiana. 369 pp</ref> While the [[amniote|higher vertebrates]] do not have gills, the gill arches form during [[Prenatal development|fetal development]], and lay the basis of essential structures such as [[jaw]]s, the [[thyroid gland]], the [[larynx]], the ''columella'' (corresponding to the [[stapes]] in [[mammals]]) and in mammals the [[Ossicles|malleus and incus]].<ref name="Romer" /> ===Central nervous system=== The vertebrates are the only [[chordate]] group to exhibit a proper [[brain]]. A slight swelling of the anterior end of the [[nerve cord]] is found in the [[lancelet]], though it lacks the eyes and other complex sense organs comparable to those of vertebrates. Other chordates do not show any trends towards cephalisation.<ref name="Romer"/> The [[central nervous system]] is based on a hollow nerve tube running along the length of the animal, from which the [[peripheral nervous system]] branches out to innervate the various systems. The front end of the nerve tube is expanded by a thickening of the walls and expansion of the [[central canal of spinal cord]] into three primary brain vesicles: The [[prosencephalon]] (forebrain), [[mesencephalon]] (midbrain) and [[rhombencephalon]] (hindbrain), further differentiated in the various vertebrate groups.<ref name=Hildebrand>Hildebrand, M. & Gonslow, G. (2001): Analysis of Vertebrate Structure. 5th edition. ''John Wiley & Sons, Inc''. [[New York]]</ref> Two laterally placed [[eye]]s form around outgrows from the midbrain, except in [[hagfish]], though this may be a secondary loss.<ref>{{cite web|url=http://www.physorg.com/news115919015.html|title=Keeping an eye on evolution|date=2007-12-03|accessdate=2007-12-04|work=PhysOrg.com}}</ref><ref>[http://tolweb.org/Hyperotreti Hyperotreti - Hagfishes]</ref> The forebrain is well developed and subdivided in most [[tetrapod]]s, while the midbrain dominate in many [[fish]] and some [[salamander]]s. Vesicles of the forebrain are usually paired, giving rise to hemispheres like the [[cerebral hemisphere]]s in [[mammals]].<ref name=Hildebrand/> The resulting anatomy of the central nervous system, with a single, hollow nerve cord topped by a series of (often paired) vesicles is unique to vertebrates. All [[invertebrates]] with well developed brains, like [[insects]], [[spiders]] and [[squids]] have a ventral rather than dorsal system of [[ganglion]]s, with a split [[brain stem]] running on each side of the mouth/gut.<ref name="Romer"/> ==Evolutionary history== {{see also|Evolution of fish|Evolution of tetrapods}} ===First vertebrates=== [[File:Haikouichthys cropped.jpg|thumb|right|The early vertebrate ''[[Haikouichthys]]'']] Vertebrates originated about 525 million years ago during the [[Cambrian explosion]], which saw the rise in organism diversity. The earliest known vertebrate is believed to be the ''[[Myllokunmingia]]''.<ref name = "Shu et al. 1999">{{cite journal|title=Lower Cambrian vertebrates from south China | author=Shu et al. |date=November 4, 1999|journal=Nature| volume=402|pages=42–46|doi= 10.1038/46965|last2=Luo|first2=H-L.|last3=Conway Morris|first3=S.|last4=Zhang|first4=X-L.|last5=Hu|first5=S-X.|last6=Chen|first6=L.|last7=Han|first7=J.|last8=Zhu|first8=M.|last9=Li|first9=Y.|issue=6757|bibcode=1999Natur.402...42S}}</ref> Another early vertebrate is ''[[Haikouichthys ercaicunensis]]''. Unlike the other fauna that dominated the Cambrian, these groups had the basic vertebrate body plan: a notochord, rudimentary vertebrae, and a well-defined head and tail.<ref>{{cite web|last=Waggoner|first=Ben|title=Vertebrates: Fossil Record|url=http://www.ucmp.berkeley.edu/vertebrates/vertfr.html|publisher=UCMP|accessdate=15 July 2011}}</ref> All of these early vertebrates lacked [[jaw]]s in the common sense and relied on filter feeding close to the seabed.<ref>{{cite book|title=The Complete Guide to Prehistoric Life|year=2005|publisher=Firefly Books|author=Tim Haines, Paul Chambers}}</ref> ===From fish to amphibians=== [[File:Acanthostega BW.jpg|thumb|''[[Acanthostega]]'', a fish-like early [[Labyrinthodontia|labyrinthodont]].]] The first [[Gnathostomata|jawed vertebrates]] appeared in the latest [[Ordovician]] and became common in the [[Devonian]], often known as the "Age of Fishes".<ref name=britannica1954>{{cite book|title=Encyclopaedia Britannica: a new survey of universal knowledge, Volume 17|year=1954|publisher=Encyclopædia Britannica|page=107}}</ref> The two groups of [[bony fishes]], the [[actinopterygii]] and [[sarcopterygii]], evolved and became common.<ref>{{cite book|title=Biology|year=2004|publisher=Cengage Learning|isbn=978-0-534-49276-2|author=Berg, Linda R.|coauthors=Eldra Pearl Solomon, Diana W. Martin|page=599}}</ref> The Devonian also saw the demise of virtually all jawless fishes, save for lampreys and hagfish, as well as the [[Placodermi]], a group of armoured fish that dominated much of the late [[Silurian]]. The Devonian also saw the rise of the first [[Labyrinthodontia|labyrinthodonts]], which was a transitional between fishes and [[amphibians]]. ===Mesozoic vertebrates=== The [[reptiles]] appeared from labyrinthodonts in the subsequent [[Carboniferous]] period. The [[anapsid]] and [[synapsid]] reptiles were common during the late [[Paleozoic]], while the [[diapsid]]s became dominant during the [[Mesozoic]]. In the sea, the [[bony fishes]] became dominant. The [[dinosaur]]s gave rise to the [[bird]]s in the [[Jurassic]].<ref>{{cite book|last=Cloudsley-Thompson|first=J. L.|title=Ecology and behaviour of Mesozoic reptiles|year=2005|publisher=Springer|location=9783540224211|page=6}}</ref> The demise of the dinosaurs at the end of the [[Cretaceous]] promoted expansion of the [[mammals]], which had evolved from the [[therapsid]]s, a group of synapsid reptiles, during the late [[Triassic]] Period. ===After the Mesozoic=== The [[Cenozoic]] world has seen great diversification of bony fishes, frogs, birds and mammals. Over half of all living vertebrate species (about 32,000 species) are fishes (non-tetrapod craniates), a diverse set of lineages that inhabit all the world's aquatic ecosystems, from snow minnows (Cypriniformes) in Himalayan lakes at elevations over 4,600 metres (15,000 feet) to flatfishes (order Pleuronectiformes) in the Challenger Deep, the deepest ocean trench at about 11,000 metres (36,000 feet). Fishes of myriad varieties are the main predators in most of the world’s water bodies, both freshwater and marine. The rest of the vertebrate species are tetrapods, a single lineage that includes amphibians (frogs, with more than 5,800 species; salamanders, with about 580 species; and caecilians, with about 175 species); mammals (with over 5,400 species); and reptiles and birds (with more than 18,000 species). Tetrapods dominate the megafauna of most terrestrial environments (including fossorial and arboreal realms) and also include many partially or fully aquatic groups (e.g., sea [[snakes]], penguins, cetaceans). == Classification == There are several ways of classifying animals. [[Evolutionary taxonomy|Evolutionary systematics]] relies on [[anatomy]], [[physiology]] and [[evolution]]ary history, which is determined through similarities in anatomy and, if possible, the [[genetics]] of organisms. [[Cladistics|Phylogenetic classification]] is based solely on [[phylogeny]].<ref>{{cite book|title=Australian water bugs: their biology and identification (Hemiptera-Heteroptera, Gerromorpha & Nepomorpha)|year=2004|publisher=Apollo Books|isbn=978-87-88757-78-1|author=Andersen, Nils Møller|coauthors=Tom A. Weir|page=38}}</ref> Evolutionary systematics gives an overview; phylogenetic systematics gives detail. The two systems are thus complementary rather than opposed.<ref>Hildebran, M. & Gonslow, G. (2001): Analysis of Vertebrate Structure. 5th edition. ''John Wiley & Sons, Inc''. [[New York]], page 33: ''Comment: The problem of naming sister groups''</ref> ===Traditional classification=== [[File:Spindle diagram.jpg|thumb|right|Traditional spindle diagram of the evolution of the vertebrates at class level]] Conventional classification has living vertebrates grouped into seven classes based on traditional interpretations of gross [[anatomy|anatomical]] and [[Physiology|physiological]] traits. This classification is the one most commonly encountered in school textbooks, overviews, non-specialist, and popular works. The [[extant taxon|extant]] vertebrates are:<ref name="Romer"/> * '''Subphylum Vertebrata''' ** Class [[Agnatha]] (jawless fishes) ** Class [[Chondrichthyes]] (cartilaginous fishes) ** Class [[Osteichthyes]] (bony fishes) ** Class [[Amphibia]] (amphibians) ** Class [[Reptilia]] (reptiles) ** Class [[Aves]] (birds) ** Class [[Mammalia]] (mammals) In addition to these comes two classes of extinct armoured fishes, the [[Placodermi]] and the [[Acanthodii]]. Other ways of classifying the vertebrates have been devised, particularly with emphasis on the [[phylogeny]] on [[labyrinthodontia|early amphibians]] and reptiles. An example based on Janvier (1981, 1997), Shu ''et al.'' (2003), and Benton (2004)<ref name="Benton2004">{{cite book | last =Benton | first =Michael J. | authorlink =Michael Benton | title =Vertebrate Palaeontology | publisher =[[Blackwell Publishing]] | date= 2004-11-01 |edition=Third | location = | pages =33, 455 pp. | url =http://palaeo.gly.bris.ac.uk/benton/vertclass.html | doi = | id = | isbn =0632056371/978-0632056378}}</ref> is given here: * '''Subphylum Vertebrata''' ** '''Superclass [[Agnatha]]''' or [[Cephalaspidomorphi]] ([[lamprey]]s and other jawless fishes) ** '''Infraphylum [[Gnathostomata]]''' (vertebrates with jaws) **** Class †[[Placodermi]] (extinct armoured fishes) **** Class [[Chondrichthyes]] (cartilaginous fishes) **** Class †[[Acanthodii]] (extinct spiny "sharks") *** '''Superclass [[Osteichthyes]]''' (bony fishes) **** Class [[Actinopterygii]] (ray-finned bony fishes) **** Class [[Sarcopterygii]] (lobe-finned fishes, some ancestral to tetrapods) *** '''Superclass [[Tetrapoda]]''' (four-limbed vertebrates) **** Class [[Amphibia]] (amphibians, some ancestral to the [[amniotes]]) **** Class †[[Synapsida]] (extinct mammal-like "reptiles", some ancestral to mammals, sometimes classed with Reptilia) **** Class [[Reptilia]] (reptiles, some ancestral to birds) **** Class [[Aves]] (birds) **** Class [[Mammalia]] (mammals) While this traditional classification is orderly, most of the groups are [[paraphyletic]], i.e. do not contain all descendants of the class's common ancestor.<ref name=Benton2004 /> For instance, descendants of the first reptiles include modern reptiles as well as birds. Most of the classes listed are not "complete" [[taxon|taxa]], meaning that they do not include all the descendants of the first representative of the group. For example, the [[agnatha]]ns have given rise to the [[Gnathostomata|jawed vertebrates]]; the [[Osteichthyes|bony fishes]] have given rise to the [[tetrapoda|land vertebrates]]; the traditional "[[Labyrinthodont|amphibians]]" have given rise to the [[Reptilia|reptiles]] (traditionally including the [[synapsid]]s, or "mammal-like "reptiles"), which in turn have given rise to the mammals and birds. Most scientists working with vertebrates use a classification based purely on [[phylogeny]], organized by their known evolutionary history and sometimes disregarding the conventional interpretations of their anatomy and physiology. ===Phylogenetic relationships=== In [[Phylogenetics|phylogenetic taxonomy]], the relationships between animals are not typically divided into ranks, but illustrated as a nested "family tree" known as a [[cladogram]]. Phylogenetic groups are given definitions based on their relationship to one another, rather than purely on physical traits such as the presence of a backbone. This nesting pattern is often combined with traditional taxonomy (as above), in a practice known as [[evolutionary taxonomy]]. The [[cladogram]] presented below is based on studies compiled by Philippe Janvier and others for the ''Tree of Life Web Project''.<ref name=tol>Janvier, Philippe. 1997. Vertebrata. Animals with backbones. Version 01 January 1997 (under construction). http://tolweb.org/Vertebrata/14829/1997.01.01 in The Tree of Life Web Project, http://tolweb.org/</ref> {{clade| style=font-size:85%;line-height:70% |label1='''Vertebrata''' |1={{clade |1=[[Hyperoartia]] (lampreys) |2=?†[[Euconodonta]] |label3=<span style="color:white;">unnamed</span> |3={{clade |1=†[[Pteraspidomorphi]] |2=?†[[Thelodonti]] |label3=<span style="color:white;">unnamed</span> |3={{clade |1=?†[[Anaspida]] |label2=<span style="color:white;">unnamed</span> |2={{clade |1=†[[Galeaspida]] |label2=<span style="color:white;">unnamed</span> |2={{clade |1=?†[[Pituriaspida]] |2=†[[Osteostraci]] |label3=[[Gnathostomata]] |3={{clade |1=†[[Placodermi]] (armoured fishes) |label2= <span style="color:white;">unnamed</span> |2={{clade |1=[[Chondrichthyes]] (cartilaginous fishes) |label2=[[Teleostomi]] |2={{clade |1=†[[Acanthodii]] |label2=[[Osteichthyes]] |2={{clade |1=[[Actinopterygii]] (ray-finned fishes) |label2=[[Sarcopterygii]] |2={{clade |1=?†[[Onychodontiformes]] |2=[[Actinistia]] (coelacanths) |label3= <span style="color:white;">unnamed</span> |3={{clade |1=†[[Porolepiformes]] |2=[[Dipnoi]] (lungfishes) }} |label4= <span style="color:white;">unnamed</span> |4={{clade |1=†[[Rhizodontidae|Rhizodontimorpha]] |2={{clade |1=†[[Tristichopteridae]] |2=[[Tetrapoda|Four limbed vertebrates]] }} }} }} }} }} }} }} }} }} }} }} }} }} == See also == * [[Invertebrate]] * [[Marine vertebrates]] ==References== {{Reflist|2}} ==Bibliography== <div class="references-small"> * {{cite book | last =Kardong | first =Kenneth V. | authorlink =Kenneth Kardong | title =Vertebrates: Comparative Anatomy, Function, Evolution | edition = second | publisher =[[McGraw-Hill]] | year= 1998 | location =USA | pages =747 pp. | url =http://www.amazon.com/Vertebrates-Comparative-Anatomy-Function-Evolution/dp/0072909560 | doi = | id = | isbn =0-07-115356-X/0-697-28654-1 }} * {{ITIS |id=331030 |taxon=Vertebrata |accessdate=6 August 2007}} </div> == External links == {{Wikispecies|Vertebrata}} * [http://tolweb.org/Vertebrata/14829 Tree of Life] * [http://www.nature.com/nature/journal/v439/n7079/abs/nature04336.html Tunicates and not cephalochordates are the closest living relatives of vertebrates] *[http://entomology.ifas.ufl.edu/fasulo/vector/chapter_07.htm Vertebrate Pests] chapter in [[United States Environmental Protection Agency]] and [[University of Florida]]/[[Institute of Food and Agricultural Sciences]] National Public Health Pesticide Applicator Training Manual {{Animalia}} {{Chordata}} [[Category:Vertebrates| ]] <!-- interwiki --> [[li:Gewervelde bieste]] [[ml:നട്ടെല്ലുള്ള ജീവികള്‍]] [[pfl:Wirbldier]] [[ckb:بڕبڕەدارەکان]]'