Editing Vertebrate (section)

== Characteristics ==

=== Unique features ===

Vertebrates belong to [[Chordate|Chordata]], a [[phylum]] characterised by five [[synapomorphies]] (unique characteristics): namely a [[notochord]], a [[dorsal nerve cord|hollow nerve cord along the back]], an [[endostyle]] (often as a [[thyroid]] gland), and pharyngeal [[gill]]s arranged in pairs. Vertebrates share these characteristics with other chordates.<ref>{{cite book |last=Freeborn |first=Michelle  |title=The fishes of New Zealand |year=2015 |publisher=Te Papa Press  |editor-last=Roberts |editor-first=Clive Douglas |volume=2 |editor-last2=Stewart |editor-first2=Andrew L. |editor-last3=Struthers |editor-first3=Carl D. |isbn=978-0-9941041-6-8 |page=6}}</ref> 

Vertebrates are distinguished from all other animals, including other chordates, by multiple synapomorphies: namely the vertebral column, skull of bone or cartilage, large brain divided into 3 or more sections, a muscular heart with multiple chambers; an inner ear with [[semicircular canals]]; sense organs including eyes, ears, and nose; and digestive organs including intestine, liver, pancreas, and stomach.<ref name="Farina 2018">{{cite web |last1=Farina |first1=Stacy |title=Vertebrate Phylogeny |url=https://static1.squarespace.com/static/534f1fe6e4b06683005e62e2/t/5b7dfcdd758d4696b0e82644/1534983398205/Biol252_E1_L2_vertebrate_phylogeny_p1_sm.pdf |publisher=Howard University |access-date=7 December 2024 |date=23 August 2018}}</ref>

=== Physical ===

{{see also|Fish anatomy}}

[[File:Vertebrate body plan.svg|thumb|center|upright=4|Idealised vertebrate body plan, showing key characteristics]]

Vertebrates (and other chordates) belong to the [[Bilateria]], a group of animals with mirror symmetrical bodies.<ref>{{cite web |title=Trends in evolution |url=https://evolution.berkeley.edu/evolibrary/article/evo_54 |publisher=[[University of California Museum of Paleontology]] |access-date=10 January 2019}}</ref> They move, typically by swimming, using [[muscle]]s along the back, supported by a strong but flexible [[Skeleton|skeletal]] structure, the spine or [[vertebral column]].<ref name="Romer 1977">{{cite book |last1=Romer |first1=Alfred S. |author1-link=Alfred Romer |last2=Parsons |first2=Thomas S. |year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders |pages=161–170 |isbn=0-03-910284-X}}</ref> The name 'vertebrate' derives from the [[Latin]] {{lang|la|vertebratus}}, 'jointed',<ref>{{cite web |title=vertebrate |work=[[Online Etymology Dictionary]] |url=http://dictionary.reference.com/browse/vertebrate}}</ref> from ''[[vertebra]]'', 'joint', in turn from Latin {{lang|la|vertere}}, 'to turn'.<ref name="MW2024">{{cite web |title=Definition of Vertebra |url=https://www.merriam-webster.com/dictionary/vertebra |website=[[Merriam-Webster]] |date=25 November 2024}}</ref>

[[File:Naturkundemuseum Berlin - Dinosaurierhalle.jpg |upright=2 |thumb |Fossilized skeleton (cast) of ''[[Diplodocus carnegii]]'', showing an extreme example of the [[vertebral column]] that gives the vertebrates their name. The species is a [[tetrapod]], its four legs adapting the fish-like body plan for walking on land. The specimen is {{cvt|26|m|ft}} long.]]

As embryos, vertebrates still have a notochord; as adults, all but the [[Agnatha|jawless fishes]] have a vertebral column, made of [[bone]] or [[cartilage]], instead.<ref name="Romer 1977"/> Vertebrate embryos have [[pharyngeal arch]]es; in adult [[fish]], these support the [[gill]]s, while in adult [[tetrapod]]s they develop into other structures.<ref name=dev>{{cite journal |last=Graham |first=A. |title=Development of the pharyngeal arches |journal=[[American Journal of Medical Genetics Part A]] |volume=119A |issue=3 |pages=251–256 |year=2003 |pmid=12784288 |doi=10.1002/ajmg.a.10980 |s2cid=28318053 }}</ref><ref name="Graham2001">{{cite journal |last=Graham |first=A. |title=The development and evolution of the pharyngeal arches |journal=[[Journal of Anatomy]] |date=July 2001 |volume=199 |issue=Pt 1-2 |pages=133–141 |doi=10.1046/j.1469-7580.2001.19910133.x |pmid=11523815|pmc=1594982 }}</ref> 

[[embryonic development|In the embryo]], a [[neural plate|layer of cells]] along the back [[neurulation|folds and fuses]] into a hollow [[neural tube]].<ref name="Martín-Durán 2018">{{cite journal |last1=Martín-Durán |first1=José M. |last2=Pang |first2=Kevin |last3=Børve |first3=Aina |last4=Lê |first4=Henrike Semmler |last5=Furu |first5=Anlaug |last6=Cannon |first6=Johanna Taylor |last7=Jondelius |first7=Ulf |last8=Hejnol |first8=Andreas |display-authors=5 |title=Convergent evolution of bilaterian nerve cords |journal=[[Nature (journal)|Nature]] |volume=553 |issue=7686 |date=4 January 2018 |pmid=29236686 |pmc=5756474 |doi=10.1038/nature25030 |doi-access=free |pages=45–50}}</ref> This develops into the [[spinal cord]], and at its front end, the [[brain]].<ref name="Martín-Durán 2018"/> The brain receives information about the world through nerves which carry signals from [[sense organ]]s in the skin and body.<ref>{{cite web |title=In brief: How does the nervous system work? |url=https://www.ncbi.nlm.nih.gov/books/NBK279390/ |website=InformedHealth.org |access-date=30 November 2024 |date=4 May 2023}}</ref> Because the ancestors of vertebrates usually moved forwards, the front of the body encountered stimuli before the rest of the body, favouring [[cephalisation]], the evolution of a head containing sense organs and a brain to process the sensory information.<ref name="Brusca 2016">{{cite book |last=Brusca |first=Richard C. |url=http://www.sinauer.com/media/wysiwyg/samples/Brusca3e_Chapter_9.pdf |chapter=Introduction to the Bilateria and the Phylum Xenacoelomorpha: Triploblasty and Bilateral Symmetry Provide New Avenues for Animal Radiation |title=Invertebrates |date=2016 |publisher=[[Sinauer Associates]] |pages=345–372 |isbn=978-1605353753}}</ref>

Vertebrates have a tubular [[Gastrointestinal tract|gut]] that extends from the [[mouth]] to the [[anus]]. The vertebral column typically continues beyond the anus to form an elongated <!--post-anal--> [[tail]].<ref name="Handrigan 2003">{{cite journal |last=Handrigan |first=Gregory R. |title=Concordia discors: duality in the origin of the vertebrate tail |journal=[[Journal of Anatomy]] |volume=202 |issue=Pt 3 |date=2003 |pmid=12713266 |pmc=1571085 |doi=10.1046/j.1469-7580.2003.00163.x |doi-access=free |pages=255–267}}</ref><ref name="Holland 2015">{{cite journal |last=Holland |first=Nicholas D. |last2=Holland |first2=Linda Z. |last3=Holland |first3=Peter W. H. |title=Scenarios for the making of vertebrates |journal=[[Nature (journal)|Nature]] |volume=520 |issue=7548 |date=23 April 2015 |doi=10.1038/nature14433 |pages=450–455}}</ref><ref name="Hejnol 2015">{{cite journal |last=Hejnol |first=Andreas |last2=Martín-Durán |first2=José M. |title=Getting to the bottom of anal evolution |journal=Zoologischer Anzeiger - A Journal of Comparative Zoology |volume=256 |date=2015 |doi=10.1016/j.jcz.2015.02.006 |doi-access=free |pages=61–74|hdl=1956/10848 |hdl-access=free }}</ref>

[[File:Gills (esox).jpg|thumb|upright=0.8|[[Branchial arch]]es bearing [[gill]]s in a [[northern pike|pike]] ]]

The ancestral<!--basal--> vertebrates, and most extant species, are [[aquatic animal|aquatic]] and carry out [[gas exchange]] in their gills. The gills are finely-branched structures which bring the blood close to the water. They are positioned just behind the head, supported by cartilaginous or bony [[branchial arch]]es.<ref>{{cite book |last=Scott |first=T. |title=Concise encyclopedia biology |year=1996 |publisher=[[De Gruyter]] |isbn=978-3-11-010661-9 |page=[https://archive.org/details/conciseencyclope00scot/page/542 542] |url-access=registration |url=https://archive.org/details/conciseencyclope00scot/page/542}}</ref> In [[jawed vertebrate]]s, the first gill arch pair evolved into the jaws.<ref>{{cite journal |title=Fossil evidence for a pharyngeal origin of the vertebrate pectoral girdle |first1=Martin D. |last1=Brazeau |first2=Marco |last2=Castiello |first3=Amin |last3=El Fassi El Fehri |first4=Louis |last4=Hamilton |first5=Alexander O. |last5=Ivanov |first6=Zerina |last6=Johanson |first7=Matt |last7=Friedman |display-authors=5 |date=20 November 2023 |journal=[[Nature (journal)|Nature]] |volume=623 |issue=7987 |pages=550–554 |doi=10.1038/s41586-023-06702-4 |bibcode=2023Natur.623..550B |doi-access=free |pmid=37914937 |pmc=10651482 |hdl=10044/1/107350 |hdl-access=free}}</ref> In [[amphibian]]s and some primitive bony fishes, the larvae have [[external gills]], branching off from the gill arches.<ref>{{cite journal |last=Szarski |first=Henryk |journal=The American Naturalist |year=1957 |volume=91 |issue=860 |pages=283–301 |title=The Origin of the Larva and Metamorphosis in Amphibia |jstor=2458911 |doi=10.1086/281990 |s2cid=85231736 }}</ref> [[Oxygen]] is carried from the gills to the body in the [[blood]], and [[carbon dioxide]] is returned to the gills, in a closed [[circulatory system]] driven by a chambered [[heart]].<ref>{{cite journal |last1=Simões-Costa |first1=Marcos S. |last2=Vasconcelos |first2=Michelle |last3=Sampaio |first3=Allysson C. |last4=Cravo |first4=Roberta M. |last5=Linhares |first5=Vania L. |last6=Hochgreb |first6=Tatiana |last7=Yan |first7=Chao Y.I. |last8=Davidson |first8=Brad |last9=Xavier-Neto |first9=José |display-authors=5 |title=The evolutionary origin of cardiac chambers |year=2005 |journal=[[Developmental Biology (journal)|Developmental Biology]] |volume=277 |issue=1 |pages=1–15 |doi=10.1016/j.ydbio.2004.09.026 |pmid=15572135}}</ref> The [[tetrapod]]s have lost the gills of their fish ancestors; they have adapted the [[swim bladder]] (that fish use for buoyancy) into [[lung]]s to breathe air, and the circulatory system is adapted accordingly.<ref name=Gaining_ground/> At the same time, they adapted the bony fins of the [[Sarcopterygii|lobe-finned fishes]] into two pairs of walking [[leg]]s, carrying the weight of the body via the [[appendicular skeleton|shoulder and pelvic girdles]].<ref name=Gaining_ground>{{cite book |last=Clack |first=J. A. |chapter=From Fins to Feet: Transformation and Transition |year=2002 |title=Gaining ground: the origin and evolution of tetrapods |publisher=[[Indiana University Press]] |pages=187–260}}</ref> 

Vertebrates vary in size from the smallest [[frog]] species such as ''[[Brachycephalus pulex]]'', with a minimum adult [[snout–vent length]] of {{convert|6.45|mm|in}}<ref name="smallest_vertebrate">{{Cite journal |last1=Bolaños |first1=Wendy H. |last2=Dias |first2=Iuri Ribeiro |last3=Solé |first3=Mirco |date=2024-02-07 |title=Zooming in on amphibians: Which is the smallest vertebrate in the world? |url=https://onlinelibrary.wiley.com/doi/10.1111/zsc.12654 |journal=[[Zoologica Scripta]] |volume=53 |issue=4 |pages=414–418 |doi=10.1111/zsc.12654 |s2cid=267599475}}</ref> to the [[blue whale]], at up to {{convert|33|m|ft|abbr=on}} and weighing some 150 tonnes.<ref>{{cite web |last1=Chamary |first1=J.V. |title=How large can animals grow? |url=https://www.discoverwildlife.com/animal-facts/how-big-or-small-could-animals-get |website=[[BBC]] Discover Wildlife |access-date=29 November 2024 |date=6 June 2024}}</ref>

=== Molecular ===

[[Molecular marker]]s known as [[conserved signature indels]] in [[protein sequence]]s have been identified and provide distinguishing criteria for the vertebrate subphylum.<ref name="Gupta 2016">{{Cite journal |last=Gupta |first=Radhey S. |date=January 2016 |title=Molecular signatures that are distinctive characteristics of the vertebrates and chordates and supporting a grouping of vertebrates with the tunicates |url=http://dx.doi.org/10.1016/j.ympev.2015.09.019 |journal=[[Molecular Phylogenetics and Evolution]] |volume=94 |issue=Pt A |pages=383–391 |doi=10.1016/j.ympev.2015.09.019 |pmid=26419477 |bibcode=2016MolPE..94..383G}}</ref> Five molecular markers are exclusively shared by all vertebrates and reliably distinguish them from all other animals; these include protein synthesis [[elongation factor-2]], [[eukaryotic translation initiation factor 3]], [[adenosine kinase]] and a protein related to [[ubiquitin carboxyl-terminal hydrolase]]).<ref name="Gupta 2016"/> A specific relationship between vertebrates and [[tunicate]]s is supported by two molecular markers, the proteins [[Rrp44]] (associated with the [[exosome complex]]) and [[serine C-palmitoyltransferase]]. These are exclusively shared by species from these two subphyla, but not by cephalochordates.<ref name="Gupta 2016"/>