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Evolution of fish
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<h2 id="overview">Overview</h2> <p class="note">Further information: <a href="/facts/Vertebrate_paleontology/6hgpg0Qh">Vertebrate paleontology</a></p> <p>Fish may have evolved from an animal similar to a coral-like <a href="/facts/Sea_squirt/Vkqqavut">sea squirt</a> (a <a href="/facts/Tunicate/9e4penn8">tunicate</a>), whose larvae resemble early fish in important ways. The first ancestors of fish may have <a href="/facts/Neoteny/t8hK3CIv">kept the larval form into adulthood</a>, as some sea squirts do today, although this path cannot be proven. </p><p><a href="/facts/Vertebrate/tT54FSTT">Vertebrates</a>, in other words the first <a href="/facts/Fish/fln4gH9V">fish</a>, originated about 530 million years ago during the <a href="/facts/Cambrian_explosion/Wg29M7PN">Cambrian explosion</a>, which saw the rise in animal diversity.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> </p> <p>The first ancestors of fish, or animals that were probably closely related to fish, were <i><a href="/facts/Haikouichthys/7t7UKhwL">Haikouichthys</a></i> and <i><a href="/facts/Myllokunmingia/YqjpstAz">Myllokunmingia</a></i>.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a><a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> These two <a href="/facts/Genus_(biology)/m8EFjSms">genera</a> all appeared around 530 <a href="/facts/Mya_(unit)/DXcnXuAw">Mya</a>. Unlike the other fauna that dominated the Cambrian, these groups had the basic vertebrate <a href="/facts/Body_plan/TykqU5bY">body plan</a>: a <a href="/facts/Notochord/wvmmQPj1">notochord</a>, rudimentary vertebrae, and a well-defined head and tail.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> All of these early vertebrates lacked <a href="/facts/Jaw/6a11Csjh">jaws</a>, relying instead on filter-feeding close to the seabed.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p><p>These were followed by indisputable fossil vertebrates in the form of heavily armoured fish discovered in rocks from the <a href="/facts/Ordovician/BjMrLIEA">Ordovician</a> period (500–430 <a href="/facts/Mya_(unit)/DXcnXuAw">Mya</a>). </p><p>The first <a href="/facts/Gnathostomata/fN7f8dKQ">jawed vertebrates</a> appeared in the late <a href="/facts/Ordovician/BjMrLIEA">Ordovician</a> and became common in the <a href="/facts/Devonian/nWgakqzk">Devonian</a>, often known as the "Age of Fishes".<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> The two groups of <a href="/facts/Osteichthyes/nXoXEj3a">bony fish</a>, the <a href="/facts/Actinopterygii/3PNaXXmJ">Actinopterygii</a> and <a href="/facts/Sarcopterygii/7Glajr07">Sarcopterygii</a>, evolved and became common.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> The Devonian saw the demise of virtually all jawless fish, save for lampreys and hagfish, as well as the <a href="/facts/Placodermi/kknCSuQ7">Placodermi</a>, a group of armoured fish that dominated much of the late <a href="/facts/Silurian/1qx4epPg">Silurian</a>, and the rise of the first <a href="/facts/Labyrinthodontia/jIXbvMu8">labyrinthodonts</a>, transitional between fish and <a href="/facts/Amphibians/r2BleD2W">amphibians</a>.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p> <p>The colonisation of new <a href="/facts/Ecological_niche/YnhNkL2e">niches</a> resulted in diversification of body plans and sometimes an increase in size. The <a href="/facts/Devonian/nWgakqzk">Devonian</a> period (395 to 345 Mya) brought in such giants as the <a href="/facts/Placoderm/kknCSuQ7">placoderm</a> <i><a href="/facts/Dunkleosteus/GPcb4wCo">Dunkleosteus</a></i>, which could grow up to seven meters long, and early air-breathing fish that could remain on land for extended periods. Among this latter group were ancestral <a href="/facts/Amphibian/r2BleD2W">amphibians</a>. </p><p>The <a href="/facts/Reptiles/04n1uKf1">reptiles</a> appeared from labyrinthodonts in the subsequent <a href="/facts/Carboniferous/BRKlkYyd">Carboniferous</a> period. The <a href="/facts/Anapsid/WpzDpent">anapsid</a> and <a href="/facts/Synapsid/uzYVtB0F">synapsid</a> amniotas were common during the late <a href="/facts/Paleozoic/5qe2wz7U">Paleozoic</a>, while the <a href="/facts/Diapsid/IFjPsvGt">diapsids</a> became dominant during the <a href="/facts/Mesozoic/yYsvXGPa">Mesozoic</a>. In the sea, the <a href="/facts/Osteichthyes/nXoXEj3a">bony fish</a> became dominant. </p><p>The later radiations, such as those of fish in the Silurian and Devonian periods, involved fewer taxa, mainly with very similar body plans. The first animals to venture onto dry land were <a href="/facts/Arthropod/JKJLTFzp">arthropods</a>. Some fish had lungs and strong, bony fins and could crawl onto the land also. </p> <h2 id="jawless-fish">Jawless fish</h2> <p class="note">Main article: <a href="/facts/Agnatha/LohAXfEH">Agnatha</a></p> <p>Jawless fish belong to the <a href="/facts/Class_(biology)/a7MrgFu3">superclass</a> <a href="/facts/Agnatha/LohAXfEH">Agnatha</a> in the <a href="/facts/Phylum_(biology)/ELT3Jyax">phylum</a> <a href="/facts/Chordate/AldL6ARm">Chordata</a>, subphylum <a href="/facts/Vertebrate/tT54FSTT">Vertebrata</a>. <i>Agnatha</i> means 'un-jawed, without jaws' (from <a href="/facts/Ancient_Greek/LIK7NlUh">Ancient Greek</a>).<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> It excludes all vertebrates with jaws, known as <a href="/facts/Gnathostomata/fN7f8dKQ">gnathostomes</a>. Although a minor element of modern marine <a href="/facts/Fauna/sMqPFxVD">fauna</a>, jawless fish were prominent among the early fish in the early <a href="/facts/Paleozoic/5qe2wz7U">Paleozoic</a>. Two types of <a href="/facts/Early_Cambrian/jIfzKtod">Early Cambrian</a> animal which apparently had fins, <a href="/facts/Vertebrate/tT54FSTT">vertebrate</a> musculature, and gills are known from the early Cambrian <a href="/facts/Maotianshan_shales/EUIL90sp">Maotianshan shales</a> of <a href="/facts/China/lTjIXY5p">China</a>: <i><a href="/facts/Haikouichthys/7t7UKhwL">Haikouichthys</a></i> and <i><a href="/facts/Myllokunmingia/YqjpstAz">Myllokunmingia</a></i>. They have been tentatively assigned to Agnatha by Janvier. A third possible agnathan from the same region is <i><a href="/facts/Haikouella/AnlSkS4j">Haikouella</a></i>. </p><p>Many <a href="/facts/Ordovician/BjMrLIEA">Ordovician</a>, <a href="/facts/Silurian/1qx4epPg">Silurian</a> and <a href="/facts/Devonian/nWgakqzk">Devonian</a> agnathians were armoured with heavy, bony, and often elaborately sculpted, plates derived from mineralized scales. The first armoured agnathans—the <a href="/facts/Ostracodermi/A4p4e6vG">ostracoderms</a>, precursors to the <a href="/facts/Osteichthyes/nXoXEj3a">bony fish</a> and hence to the <a href="/facts/Tetrapoda/vWpAxzAW">tetrapods</a> (including humans)—are known from the Middle <a href="/facts/Ordovician/BjMrLIEA">Ordovician</a>, and by the Late <a href="/facts/Silurian/1qx4epPg">Silurian</a> the agnathans had reached the high point of their evolution. Most of the ostracoderms, such as <a href="/facts/Thelodonti/TQIr3egY">thelodonts</a>, <a href="/facts/Osteostraci/1ktwsM5j">osteostracans</a> and <a href="/facts/Galeaspida/RQlm1AlQ">galeaspids</a>, were more closely related to the gnathostomes than to the surviving agnathans, known as cyclostomes. Cyclostomes apparently split from other agnathans before the evolution of dentine and bone, which are present in many fossil agnathans, including <a href="/facts/Conodont/wqA7V7cz">conodonts</a>.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> Agnathans declined in the <a href="/facts/Devonian/nWgakqzk">Devonian</a> and never recovered. </p><p>The agnathans as a whole are <a href="/facts/Paraphyly/tmTWjACz">paraphyletic</a>,<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> because most extinct agnathans belong to the <a href="/facts/Stem_group/fHDhwp5x">stem group</a> of the gnathostomes, the jawed fish that evolved from them.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a><a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> Molecular data, both from rRNA<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> and from mtDNA<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> strongly supports the theory that living agnathans, known as <a href="/facts/Cyclostomata/gack6fgX">cyclostomes</a>, are <a href="/facts/Monophyletic/pD8Yrrn6">monophyletic</a>.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> In <a href="/facts/Phylogenetics/bw4rsovt">phylogenetic taxonomy</a>, the relationships between animals are not typically divided into ranks, but illustrated as a nested "family tree" known as a <a href="/facts/Cladogram/fWFYhUFo">cladogram</a>. 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, in a practice known as <a href="/facts/Evolutionary_taxonomy/Sr5jTvWb">evolutionary taxonomy</a>. </p> <p>The <a href="/facts/Cladogram/fWFYhUFo">cladogram</a> for jawless fish is based on studies by <a href="/facts/Philippe_Janvier/xKt7JUt2">Philippe Janvier</a> and others for the <i>Tree of Life Web Project</i>.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> (†=group is extinct) </p> <table><tbody><tr><td><a href="/facts/Agnatha/LohAXfEH">Jawless fish</a></td><td rowspan="2"><table><tbody><tr><td></td><td rowspan="2"><p><a href="/facts/Hyperoartia/y7epYLm7">Hyperoartia</a> (lampreys)</p></td></tr><tr><td></td></tr><tr><td></td><td rowspan="2"><p>?†<a href="/facts/Euconodonta/wqA7V7cz">Euconodonta</a> (eel-like animals)</p></td></tr><tr><td></td></tr><tr><td>unnamed</td><td rowspan="2"><table><tbody><tr><td></td><td rowspan="2"><p>†<a href="/facts/Pteraspidomorphi/8gz6Vzq6">Pteraspidomorphi</a> (jawless fish)</p></td></tr><tr><td></td></tr><tr><td></td><td rowspan="2"><p>?†<a href="/facts/Thelodonti/TQIr3egY">Thelodonti</a> (jawless fish with scales)</p></td></tr><tr><td></td></tr><tr><td>unnamed</td><td rowspan="2"><table><tbody><tr><td></td><td rowspan="2"><p>?†<a href="/facts/Anaspida/cLsa13dQ">Anaspida</a></p></td></tr><tr><td></td></tr><tr><td>unnamed</td><td rowspan="2"><table><tbody><tr><td></td><td rowspan="2"><p>†<a href="/facts/Galeaspida/RQlm1AlQ">Galeaspida</a> (jawless fish with bone head shields)</p></td></tr><tr><td></td></tr><tr><td>unnamed</td><td rowspan="2"><table><tbody><tr><td></td><td rowspan="2"><p>?†<a href="/facts/Pituriaspida/VCSrqb9v">Pituriaspida</a> (armoured jawless fish with large rostrums)</p></td></tr><tr><td></td></tr><tr><td></td><td rowspan="2"><p>†<a href="/facts/Osteostraci/1ktwsM5j">Osteostraci</a> (bony armoured jawless fish with heads covered with a bony shield)</p></td></tr><tr><td></td></tr><tr><td></td><td rowspan="2"><p><a href="/facts/Gnathostomata/fN7f8dKQ">Jawed vertebrates</a> → continued in section below</p></td></tr><tr><td></td></tr></tbody></table></td></tr><tr><td></td></tr></tbody></table></td></tr><tr><td></td></tr></tbody></table></td></tr><tr><td></td></tr></tbody></table></td></tr><tr><td></td></tr></tbody></table></td></tr><tr><td></td></tr></tbody></table> <h3>†Conodonts</h3> <p><a href="/facts/Conodont/wqA7V7cz">Conodonts</a> resembled primitive jawless eels. They appeared 520 Ma ago and were wiped out 200 Ma ago.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> Initially they were known only from tooth-like microfossils called <i>conodont elements</i>. These "teeth" have been variously interpreted as filter-feeding apparatuses or as a "grasping and crushing array".<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> Conodonts ranged in length from a centimetre to the 40 cm <i><a href="/facts/Promissum/1wn81nmx">Promissum</a></i>. Their large eyes had a lateral position, which makes a predatory role unlikely. The preserved musculature hints that some conodonts (<i>Promissum</i> at least) were efficient cruisers but incapable of bursts of speed.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> In 2012 researchers classified the conodonts in the <a href="/facts/Phylum_(biology)/ELT3Jyax">phylum</a> <a href="/facts/Chordata/AldL6ARm">Chordata</a> on the basis of their fins with fin rays, <a href="/facts/Chevron_(insignia)/gl7MaJsS">chevron</a>-shaped muscles and <a href="/facts/Notochord/wvmmQPj1">notochord</a>.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> Some researchers see them as vertebrates similar in appearance to modern <a href="/facts/Hagfish/pEgPuk4v">hagfish</a> and <a href="/facts/Lamprey/nxgTvh0z">lampreys</a>,<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> though <a href="/facts/Phylogenetic/bw4rsovt">phylogenetic</a> analysis suggests that they are more <a href="/facts/Synapomorphy/t21GWRl1">derived</a> than either of these groups.<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> </p> <h3>†Ostracoderms</h3> <p><a href="/facts/Ostracoderm/A4p4e6vG">Ostracoderms</a> (lit. 'shell-skinned') are <a href="/facts/Armour_(zoology)/BYvjkjtz">armoured</a> <a href="/facts/Agnatha/LohAXfEH">jawless fish</a> of the <a href="/facts/Paleozoic/5qe2wz7U">Paleozoic</a>. The term does not often appear in classifications today because the taxon is <a href="/facts/Paraphyly/tmTWjACz">paraphyletic</a> or <a href="/facts/Polyphyly/o7lxKY74">polyphyletic</a>, and has no phylogenetic meaning.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a> However, the term is still used informally to group together the armoured jawless fish. </p><p>The ostracoderm armour consisted of 3–5 mm polygonal plates that shielded the head and gills, and then overlapped further down the body like scales. The eyes were particularly shielded. Earlier <a href="/facts/Chordate/AldL6ARm">chordates</a> used their <a href="/facts/Gill/FWgM3Jp8">gills</a> for both respiration and feeding, whereas ostracoderms used their gills for <a href="/facts/Respiration_(physiology)/KKWAJIbd">respiration</a> only. They had up to eight separate pharyngeal gill pouches along the side of the head, which were permanently open with no protective <a href="/facts/Operculum_(fish)/zKrTfJUm">operculum</a>. Unlike <a href="/facts/Invertebrate/3CyqCVnN">invertebrates</a> that use <a href="/facts/Cilium/C9l436HM">ciliated</a> motion to move food, ostracoderms used their muscular pharynx to create a suction that pulled small and slow-moving <a href="/facts/Prey/JEGdrX3f">prey</a> into their mouths. </p><p>The first fossil fish that were discovered were ostracoderms. The <a href="/facts/Switzerland/LcGuxeTe">Swiss</a> anatomist <a href="/facts/Louis_Agassiz/W3DJ3zFN">Louis Agassiz</a> received some fossils of bony armored fish from <a href="/facts/Scotland/VGwbbxB2">Scotland</a> in the 1830s. He had a hard time classifying them as they did not resemble any living creature. He compared them at first with extant armored fish such as <a href="/facts/Catfish/SHrSxpuH">catfish</a> and <a href="/facts/Sturgeon/mt8TC3t8">sturgeons</a> but later, realizing that they had no movable jaws, classified them in 1844 into a new group "ostracoderms".<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> </p><p>Ostracoderms existed in two major groups, the more primitive <a href="/facts/Heterostraci/wME1o3rh">heterostracans</a> and the <a href="/facts/Cephalaspidomorphi/4fleBg3K">cephalaspids</a>. Later, about 420 million years ago, the jawed fish evolved from one of the ostracoderms. After the appearance of jawed fish, most ostracoderm species underwent a decline, and the last ostracoderms became extinct at the end of the <a href="/facts/Devonian_period/nWgakqzk">Devonian period</a>.<a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a> </p> <h2 id="jawed-fish">Jawed fish</h2> <p class="note">Further information: <a href="/facts/Jawed_fish/fN7f8dKQ">Jawed fish</a> and <a href="/facts/Evolution_of_jaws/raQDVv03">Evolution of jaws</a></p> <p>The vertebrate jaw probably originally evolved in the <a href="/facts/Silurian/1qx4epPg">Silurian</a> period and appeared in the <a href="/facts/Placodermi/kknCSuQ7">Placoderm</a> <a href="/facts/Fish/fln4gH9V">fish</a>, which further diversified in the <a href="/facts/Devonian/nWgakqzk">Devonian</a>. The two most anterior <a href="/facts/Pharyngeal_arch/12PBkJEN">pharyngeal arches</a> are thought to have become the jaw itself and the hyoid arch, respectively. The hyoid system suspends the jaw from the braincase of the skull, permitting great mobility of the jaws. Already long assumed to be a paraphyletic assemblage leading to more derived gnathostomes, the discovery of <i><a href="/facts/Entelognathus/EL3H3A1j">Entelognathus</a></i> suggests that placoderms are directly ancestral to modern bony fish. </p><p>As in most <a href="/facts/Vertebrate/tT54FSTT">vertebrates</a>, fish jaws are <a href="/facts/Bone/kwJaR6IQ">bony</a> or <a href="/facts/Cartilage/vxy2qzKN">cartilaginous</a> and oppose vertically, comprising an <i>upper jaw</i> and a <i>lower jaw</i>. The jaw is derived from the most anterior two <a href="/facts/Pharyngeal_arch/12PBkJEN">pharyngeal arches</a> supporting the gills, and usually bears numerous <a href="/facts/Teeth/Wc6IqwVf">teeth</a>. The skull of the last common ancestor of today's jawed vertebrates is assumed to have resembled sharks.<a class="footnote-ref" id="fnref:27" href="#fn:27"><sup>27</sup></a> </p><p>It is thought that the original selective advantages offered by the jaw were not related to feeding, but to increases in respiration efficiency. The jaws were used in the <a href="/facts/Buccal_pump/mNfT11AU">buccal pump</a> (observable in modern fish and <a href="/facts/Amphibians/r2BleD2W">amphibians</a>) that pumps water across the gills of fish or air into the lungs in the case of amphibians. Over evolutionary time the more familiar use of jaws (to humans) in feeding was selected for and became a very important function in vertebrates. Many <a href="/facts/Teleostei/1YULPGW5">teleost</a> fish have substantially modified their jaws for <a href="/facts/Suction_feeding/Fow990hf">suction feeding</a> and <a href="/facts/Jaw_protrusion/raQDVv03">jaw protrusion</a>, resulting in highly complex jaws with dozens of bones involved. </p><p> Jawed vertebrates and jawed fish evolved from earlier jawless fish. The <a href="/facts/Cladogram/fWFYhUFo">cladogram</a> for jawed vertebrates is a continuation of the cladogram in the section above. (†=extinct)</p> <table><tbody><tr><td><a href="/facts/Gnathostomata/fN7f8dKQ">Jawed vertebrates</a></td><td rowspan="2"><table><tbody><tr><td></td><td rowspan="2"><p>†<a href="/facts/Placodermi/kknCSuQ7">Placodermi</a> (armoured fish) </p></td></tr><tr><td></td></tr><tr><td>unnamed</td><td rowspan="2"><table><tbody><tr><td></td><td rowspan="2"><p><a href="/facts/Acanthodians/tshDhfzW">Acanthodians</a> and <a href="/facts/Chondrichthyes/xcW7PJDU">Chondrichthyes</a> (cartilaginous fish) </p></td></tr><tr><td></td></tr><tr><td><a href="/facts/Osteichthyes/nXoXEj3a">Bony fish</a></td><td rowspan="2"><table><tbody><tr><td></td><td rowspan="2"><p><a href="/facts/Actinopterygii/3PNaXXmJ">Actinopterygii</a> (ray-finned fish), dominant class of fish today </p></td></tr><tr><td></td></tr><tr><td><a href="/facts/Sarcopterygii/7Glajr07">Lobe-finned fish</a></td><td rowspan="2"><table><tbody><tr><td></td><td rowspan="2"><p>?†<a href="/facts/Onychodontiformes/W5j9Ft9A">Onychodontiformes</a> (lobe-finned) </p></td></tr><tr><td></td></tr><tr><td></td><td rowspan="2"><p><a href="/facts/Actinistia/1aoMLyN3">Actinistia</a> (coelacanths) </p></td></tr><tr><td></td></tr><tr><td>unnamed</td><td rowspan="2"><table><tbody><tr><td></td><td rowspan="2"><p>†<a href="/facts/Porolepiformes/d8r3f8M9">Porolepiformes</a> (lobe-finned) </p></td></tr><tr><td></td></tr><tr><td></td><td rowspan="2"><p><a href="/facts/Dipnoi/oNNrFFoE">Dipnoi</a> (lungfish) </p></td></tr><tr><td></td></tr></tbody></table></td></tr><tr><td></td></tr><tr><td>unnamed</td><td rowspan="2"><table><tbody><tr><td></td><td rowspan="2"><p>†<a href="/facts/Rhizodontidae/jXWxXGz2">Rhizodontimorpha</a> (predatory lobe-finned) </p></td></tr><tr><td></td></tr><tr><td></td><td rowspan="2"><table><tbody><tr><td></td><td rowspan="2"><p>†<a href="/facts/Tristichopteridae/5tRmcG3m">Tristichopteridae</a> (<a href="/facts/Tetrapodomorph/rxUSNa98">tetrapodomorphs</a>) </p></td></tr><tr><td></td></tr><tr><td></td><td rowspan="2"><p><a href="/facts/Tetrapoda/vWpAxzAW">Tetrapods</a> (four-legged animals) </p></td></tr><tr><td></td></tr></tbody></table></td></tr><tr><td></td></tr></tbody></table></td></tr><tr><td></td></tr></tbody></table></td></tr><tr><td></td></tr></tbody></table></td></tr><tr><td></td></tr></tbody></table></td></tr><tr><td></td></tr></tbody></table></td></tr><tr><td></td></tr></tbody></table> <h3>†Placoderms</h3> <p class="note">Further information: <a href="/facts/Placodermi/kknCSuQ7">Placodermi</a> and <a href="/facts/List_of_placoderms/VPGDNcQs">List of placoderms</a></p> <p>Placoderms, <a href="/facts/Class_(biology)/a7MrgFu3">class</a> <a href="/facts/Placodermi/kknCSuQ7">Placodermi</a> ('plate-skinned'), are <a href="/facts/Extinction/24p5NP2q">extinct</a> armoured prehistoric fish, which appeared about 430 Ma in the Early to Middle Silurian. They were mostly wiped out during the <a href="/facts/Late_Devonian_extinction/gkThyMzz">Late Devonian extinction</a> event, 378 Ma, though some survived and made a slight recovery in diversity during the <a href="/facts/Famennian/1JpyeaRS">Famennian</a> epoch before dying out entirely at the close of the Devonian, 360 mya; they are ultimately ancestral to modern gnathostome vertebrates.<a class="footnote-ref" id="fnref:28" href="#fn:28"><sup>28</sup></a><a class="footnote-ref" id="fnref:29" href="#fn:29"><sup>29</sup></a> Their head and thorax were covered with massive and often ornamented armoured plates. The rest of the body was <a href="/facts/Fish_scale/MS2brwuo">scaled</a> or naked, depending on the species. The armour shield was articulated, with the head armour hinged to the thoracic armour. This allowed placoderms to lift their heads, unlike ostracoderms. Placoderms were the first jawed fish; their jaws likely evolved from the first of their <a href="/facts/Gill/FWgM3Jp8">gill</a> arches. The chart on the right shows the rise and demise of the separate placoderm lineages: <a href="/facts/Acanthothoraci/8gLpYur1">Acanthothoraci</a>, <a href="/facts/Rhenanida/7TTw1j1E">Rhenanida</a>, <a href="/facts/Antiarchi/YUolYXdx">Antiarchi</a>, <a href="/facts/Petalichthyidae/7jKKmmpc">Petalichthyidae</a>, <a href="/facts/Ptyctodontida/6krDPD8K">Ptyctodontida</a> and <a href="/facts/Arthrodira/htk54jt2">Arthrodira</a>. </p> <h3>†Spiny sharks</h3> <p class="note">Main article: <a href="/facts/Acanthodii/tshDhfzW">Acanthodii</a></p> <p>Spiny sharks, class <a href="/facts/Acanthodii/tshDhfzW">Acanthodii</a>, are extinct fish that share features with both bony and cartilaginous fish, though ultimately more closely related to and ancestral to the latter. Despite being called "spiny sharks", acanthodians predate sharks, though they gave rise to them. They evolved in the sea at the beginning of the Silurian period, some 50 million years before the first sharks appeared. Eventually competition from bony fish proved too much, and the spiny sharks died out in Permian times about 250 Ma. In form they resembled sharks, but their <a href="/facts/Epidermis/JvRABubP">epidermis</a> was covered with tiny rhomboid platelets like the scales of <a href="/facts/Holostei/aot3VGm4">holosteans</a> (<a href="/facts/Gar/5Y2b5ayb">gars</a>, <a href="/facts/Bowfin/QWtK6rkA">bowfins</a>). </p> <h3>Cartilaginous fish</h3> <p class="note">Further information: <a href="/facts/List_of_prehistoric_cartilaginous_fish_genera/J8tboPK7">List of prehistoric cartilaginous fish genera</a></p> <p>Cartilaginous fish, class <a href="/facts/Chondrichthyes/xcW7PJDU">Chondrichthyes</a>, consisting of <a href="/facts/Shark/rh5Cotvx">sharks</a>, <a href="/facts/Batoidea/4w6wfqlh">rays</a> and <a href="/facts/Chimaera/gUmgE3Jl">chimaeras</a>, appeared by about 395 million years ago, in the Middle <a href="/facts/Devonian/nWgakqzk">Devonian</a>, evolving from acanthodians. The class contains the subclasses <a href="/facts/Holocephali/9gFKBV35">Holocephali</a> (<a href="/facts/Chimaera/gUmgE3Jl">chimaeras</a>) and <a href="/facts/Elasmobranchii/6rBrf5w6">Elasmobranchii</a> (<a href="/facts/Shark/rh5Cotvx">sharks</a> and <a href="/facts/Batoidea/4w6wfqlh">rays</a>). The radiation of elasmobranches in the chart on the right is divided into the following taxa: <a href="/facts/Cladoselache/qDV9efww">Cladoselache</a>, <a href="/facts/Eugeneodontiformes/z8l8LHX2">Eugeneodontiformes</a>, <a href="/facts/Symmoriida/r2rDwbjS">Symmoriida</a>, <a href="/facts/Xenacanthiformes/d3nFBEr1">Xenacanthiformes</a>, <a href="/facts/Ctenacanthiformes/Daxjy06c">Ctenacanthiformes</a>, <a href="/facts/Hybodontiformes/T6D01okh">Hybodontiformes</a>, <a href="/facts/Galeomorphii/UEXhruYg">Galeomorphii</a>, <a href="/facts/Squaliformes/aPjJxtbk">Squaliformes</a> and <a href="/facts/Batoidea/4w6wfqlh">Batoidea</a>. </p> <h3>Bony fish</h3> <p class="note">Further information: <a href="/facts/Osteichthyes/nXoXEj3a">Osteichthyes</a> and <a href="/facts/List_of_prehistoric_bony_fish_genera/SDIyqrJz">List of prehistoric bony fish genera</a></p> <p>Bony fish, class <a href="/facts/Osteichthyes/nXoXEj3a">Osteichthyes</a>, are characterised by bony skeleton rather than <a href="/facts/Cartilage/vxy2qzKN">cartilage</a>. They appeared in the late <a href="/facts/Silurian/1qx4epPg">Silurian</a>, about 419 million years ago. The recent discovery of <i><a href="/facts/Entelognathus/EL3H3A1j">Entelognathus</a></i> strongly suggests that bony fish (and possibly cartilaginous fish, via acanthodians) evolved from early placoderms.<a class="footnote-ref" id="fnref:30" href="#fn:30"><sup>30</sup></a> A subclass of the Osteichthyes, the ray-finned fish (<a href="/facts/Actinopterygii/3PNaXXmJ">Actinopterygii</a>), have become the <a href="/facts/Dominance_(ecology)/uqRC9f4s">dominant group</a> of fish in the post-Paleozoic and modern world, with some 30,000 living species. The bony (and cartilaginous) fish groups that emerged after the Devonian were characterised by steady improvements in foraging and locomotion.<a class="footnote-ref" id="fnref:31" href="#fn:31"><sup>31</sup></a> </p> <h4>Lobe-finned fish</h4> <p class="note">Further information: <a href="/facts/Sarcopterygii/7Glajr07">Sarcopterygii</a></p> <p>Lobe-finned fish, fish belonging to the class <a href="/facts/Sarcopterygii/7Glajr07">Sarcopterygii</a>, are mostly extinct bony fish, basally characterised by robust and stubby lobe fins containing a robust internal skeleton, <a href="/facts/Cosmoid_scale/MS2brwuo">cosmoid scales</a> and internal nostrils. Their fins are fleshy, <a href="/facts/Lobe_(anatomy)/Mc0Xa4s4">lobed</a>, and paired, joined to the body by a single bone.<a class="footnote-ref" id="fnref:32" href="#fn:32"><sup>32</sup></a> The fins of lobe-finned fish differ from those of all other fish in that each is borne on a fleshy, lobelike, scaly stalk extending from the body. The <a href="/facts/Pectoral_fin/kS10PMPf">pectoral</a> and <a href="/facts/Pelvic_fin/YgynRkfE">pelvic fins</a> are articulated in ways resembling the tetrapod limbs they were the precursors to. The fins evolved into the legs of the first tetrapod land vertebrates, <a href="/facts/Amphibian/r2BleD2W">amphibians</a>. They also possess two dorsal fins with separate bases, as opposed to the single dorsal fin of <a href="/facts/Ray-finned_fish/3PNaXXmJ">ray-finned fish</a>. The braincase of lobe-finned fish primitively has a hinge line, but this is lost in tetrapods and lungfish. Many early lobe-finned fish have a symmetrical tail. All lobe-finned fish possess teeth covered with true <a href="/facts/Tooth_enamel/ffUMmssl">enamel</a>. </p><p>Lobe-finned fish, such as <a href="/facts/Coelacanth/TaEXps8Q">coelacanths</a> and <a href="/facts/Lungfish/oNNrFFoE">lungfish</a>, were the most diverse group of bony fish in the Devonian. Taxonomists who subscribe to the cladistic approach include the grouping <a href="/facts/Tetrapoda/vWpAxzAW">Tetrapoda</a> within the Sarcopterygii, and the tetrapods in turn include all species of four-limbed vertebrates.<a class="footnote-ref" id="fnref:33" href="#fn:33"><sup>33</sup></a> The fin-limbs of lobe-finned fish such as the coelacanths show a strong similarity to the expected ancestral form of tetrapod limbs. The lobe-finned fish apparently followed two different lines of development and are accordingly separated into two subclasses, the <a href="/facts/Rhipidistia/qawK0f0B">Rhipidistia</a> (including the lungfish, and the <a href="/facts/Tetrapodomorpha/rxUSNa98">Tetrapodomorpha</a>, which include the Tetrapoda) and the <a href="/facts/Actinistia/1aoMLyN3">Actinistia</a> (coelacanths). The first lobe-finned fish, found in the uppermost <a href="/facts/Silurian/1qx4epPg">Silurian</a> (c. 418 Mya), closely resembled <a href="/facts/Spiny_shark/tshDhfzW">spiny sharks</a>, which became extinct at the end of the Paleozoic. In the Early to Middle <a href="/facts/Devonian/nWgakqzk">Devonian</a> (416–385 Mya), while the predatory <a href="/facts/Placodermi/kknCSuQ7">placoderms</a> dominated the seas, some lobe-finned fish came into <a href="/facts/Freshwater/xMP2TxwI">freshwater</a> habitats. </p> <p>In the Early Devonian (416-397 Mya), the lobe-finned fish split into two main lineages — the <a href="/facts/Coelacanth/TaEXps8Q">coelacanths</a> and the <a href="/facts/Rhipidistia/qawK0f0B">rhipidistians</a>. The heyday of the former was the Late <a href="/facts/Devonian/nWgakqzk">Devonian</a> and <a href="/facts/Carboniferous/BRKlkYyd">Carboniferous</a>, from 385 to 299 Mya, as they were more common during those periods than in any other period in the Phanerozoic; coelacanths still live today in the <a href="/facts/Ocean/8W8lYgjD">oceans</a> (genus <i><a href="/facts/Latimeria/L9WsSLeP">Latimeria</a></i>). The Rhipidistians, whose ancestors probably lived in <a href="/facts/Estuary/WmkSInmK">estuaries</a>, migrated into freshwater habitats. They in turn split into two major groups: the <a href="/facts/Lungfish/oNNrFFoE">lungfish</a> and the <a href="/facts/Tetrapodomorph/rxUSNa98">tetrapodomorphs</a>. The lungfish's greatest diversity was in the <a href="/facts/Triassic/r6CNxKXC">Triassic</a> period; today there are three genera left.<a class="footnote-ref" id="fnref:34" href="#fn:34"><sup>34</sup></a> The lungfish evolved the first proto-lungs and proto-limbs, developing the ability to live outside a water environment in the Middle Devonian (397–385 Mya). The first tetrapodomorphs, which included the gigantic rhizodonts, had the same general anatomy as the lungfish, who were their closest kin, but they appear not to have left their water habitat until the Late Devonian epoch (385–359 Mya), with the appearance of <a href="/facts/Tetrapoda/vWpAxzAW">tetrapods</a> (four-legged vertebrates). Lobe-finned fish continued until towards the end of Paleozoic era, suffering heavy losses during the <a href="/facts/Permian-Triassic_extinction_event/d8kI8Mfn">Permian-Triassic extinction event</a> (251 Mya). </p> <h4>Ray-finned fish</h4> <p>Ray-finned fish, class <a href="/facts/Actinopterygii/3PNaXXmJ">Actinopterygii</a>, differ from lobe-finned fish in that their fins consist of webs of skin supported by spines ("rays") made of bone or horn. There are other differences in respiratory and circulatory structures. Ray-finned fish normally have skeletons made from true bone, though this is not true of <a href="/facts/Sturgeons/mt8TC3t8">sturgeons</a> and <a href="/facts/Paddlefish/0U6RuF18">paddlefish</a>.<a class="footnote-ref" id="fnref:35" href="#fn:35"><sup>35</sup></a> </p><p>Ray-finned fish are a dominant vertebrate group, containing half of all known vertebrate species. They inhabit abyssal depths in the sea, coastal inlets and freshwater rivers and lakes, and are a major source of food for humans.<a class="footnote-ref" id="fnref:36" href="#fn:36"><sup>36</sup></a> </p> <h2 id="timeline">Timeline</h2> <p class="note">Main article: <a href="/facts/Timeline_of_fish_evolution/1EqkpySu">Timeline of fish evolution</a></p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Comparative_anatomy/UycBTvDH">Comparative anatomy</a></li> <li><a href="/facts/Evolution_of_paired_fins/kS10PMPf">Evolution of paired fins</a></li> <li><a href="/facts/Ichthyolith/wDJx7ugz">Ichthyolith</a></li> <li><a href="/facts/List_of_examples_of_convergent_evolution/GLd7WlMu">Convergent evolution in fish</a></li> <li><a href="/facts/List_of_fossil_sites/6gYhEPes">List of fossil sites</a></li> <li><a href="/facts/Lists_of_prehistoric_fish/l26dU8Mc">Lists of prehistoric fish</a></li> <li><a href="/facts/List_of_years_in_paleontology/D3Xg8MbR">List of years in paleontology</a></li> <li><a href="/facts/Old_Red_Sandstone/G72XzJxm">Old Red Sandstone</a></li> <li><a href="/facts/Parodies_of_the_ichthys_symbol/btME6bXc">Parodies of the ichthys symbol</a></li> <li><a href="/facts/History_of_life/Ss6eB0EX">History of life</a></li> <li><a href="/facts/Walking_fish/T2uuSMul">Walking fish</a> - fish with tetrapod-like features</li> <li><a href="/facts/Vertebrate_paleontology/6hgpg0Qh">Vertebrate paleontology</a></li></ul> <h2 id="sources">Sources</h2> <ul><li><a href="/facts/Michael_Benton/Kb1yDBny">Benton, Michael J.</a> (2005). <i>Vertebrate Palaeontology</i>.</li> <li>Berg, Linda R.; Eldra Pearl Solomon; Diana W. Martin (2004). <i>Biology</i>. Cengage Learning. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-534-49276-2.</li> <li>Encyclopædia Britannica (1954). <i>Encyclopædia Britannica: A new survey of universal knowledge</i>. Vol. 17.</li> <li>Helfman, G.; Collette, B.; Facey, D.; Bowen, B. (2009). <a href="http://www.blackwellpublishing.com/helfman/"><i>The Diversity of Fishes: Biology, Evolution, and Ecology</i></a> (2nd ed.). Wiley-Blackwell. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-1-4051-2494-2. <a href="https://web.archive.org/web/20210826212914/http://www.blackwellpublishing.com/helfman/">Archived</a> from the original on 26 August 2021. Retrieved 26 January 2010.</li> <li>Nelson, Joseph S. (2006). <a href="/facts/Fishes_of_the_World/DRNmGe54"><i>Fishes of the World</i></a>. <a href="/facts/John_Wiley_%26_Sons/53g3LqJc">John Wiley & Sons</a>. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-471-25031-9.</li> <li>Romer, A.S. (1970). <i>The Vertebrate Body</i> (4 ed.). London: W.B. Saunders.</li></ul> <h2 id="further-reading">Further reading</h2> <ul><li>Benton, M.J. (1998) <a href="http://palaeo.gly.bris.ac.uk/Essays/vertfr/default.html">"The quality of the fossil record of the vertebrates"</a> <a href="https://web.archive.org/web/20120825065925/http://palaeo.gly.bris.ac.uk/Essays/vertfr/default.html">Archived</a> 25 August 2012 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a> Pages 269–303 in Donovan, S.K. and Paul, C.R.C. (eds), <i>The adequacy of the fossil record</i>. Wiley. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 9780471969884.</li> <li>Cloutier, R. (2010). "The fossil record of fish ontogenies: Insights into developmental patterns and processes". <i>Seminars in Cell & Developmental Biology</i>. 21 (4): 400–413. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1016%2Fj.semcdb.2009.11.004">10.1016/j.semcdb.2009.11.004</a>. <a href="/facts/PMID_(identifier)/JlHAvMHt">PMID</a> <a href="https://pubmed.ncbi.nlm.nih.gov/19914384">19914384</a>.</li> <li>Janvier, Philippe (1998) <i>Early Vertebrates</i>, Oxford, New York: Oxford University Press. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 0-19-854047-7</li> <li>Long, John A. (1996) <a href="https://books.google.com/books?id=dEP_kQAACAAJ&q=%22The+rise+of+fishes%22"><i>The Rise of Fishes: 500 Million Years of Evolution</i></a> Johns Hopkins University Press. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 0-8018-5438-5</li> <li>McKenzie, D.J.; Farrell, A.P.; and Brauner, C.J. (2011) <a href="https://books.google.com/books?id=gfBc_omOIeAC&q=%22Fish+physiology%22"><i>Fish Physiology: Primitive Fishes</i></a> Academic Press. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 9780080549521.</li> <li>Maisey, J.G. (1996) <a href="https://books.google.com/books?id=gAiAPwAACAAJ&q=editions:_y8O0MW7spIC"><i>Fossil Fishes</i></a> Holt. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 9780805043662.</li> <li>Near, T.J.; Dornburg, A.; Eytan, R.I.; Keck, B.P.; Smith, W.L.; Kuhn, K.L.; Moore, J.A.; Price, S.A.; Burbrink, F.T.; Friedman, M. (2013). <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3732986">"Phylogeny and tempo of diversification in the superradiation of spiny-rayed fishes"</a>. <i>Proceedings of the National Academy of Sciences</i>. 110 (31): 12738–12743. <a href="/facts/Bibcode_(identifier)/9HtdQSGB">Bibcode</a>:<a href="https://ui.adsabs.harvard.edu/abs/2013PNAS..11012738N">2013PNAS..11012738N</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1073%2Fpnas.1304661110">10.1073/pnas.1304661110</a>. <a href="/facts/PMC_(identifier)/dX1zMt71">PMC</a> <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3732986">3732986</a>. <a href="/facts/PMID_(identifier)/JlHAvMHt">PMID</a> <a href="https://pubmed.ncbi.nlm.nih.gov/23858462">23858462</a>.</li> <li><a href="/facts/Neil_Shubin/FtW3fMS9">Shubin, Neil</a> (2009) <a href="https://books.google.com/books?id=c008kdNwR1cC&q=%22Your+Inner+Fish%22"><i>Your inner fish: A journey into the 3.5-billion-year history of the human body</i></a> Vintage Books. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 9780307277459.</li> <li><a href="http://www.ucmp.berkeley.edu/vertebrates/vertintro.html">Introduction to the Vertebrates</a> <i>University of California Museum of Palaeontology</i>.</li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="http://hoopermuseum.earthsci.carleton.ca/12.html">Fossil Fish</a></li> <li><a href="https://web.archive.org/web/20130724153811/http://ukwetlandhabitats.co.uk/fishbiologyandbehavior.html">Origins of Fish</a></li> <li><a href="https://www.youtube.com/watch?v=gZpsVSVRsZk">Overview of evolution</a> – <a href="/facts/Carl_Sagan/HhdhTggo">Carl Sagan</a></li> <li><a href="http://www.ibiology.org/ibioseminars/evolution-ecology/marc-w-kirschner-part-1.html">The Origin of Vertebrates</a> <a href="/facts/Marc_W._Kirschner/UUJh55JW">Marc W. Kirschner</a>, <i>iBioSeminars</i>.</li> <li><a href="http://blogs.scientificamerican.com/artful-amoeba/2013/08/29/150-million-years-of-fish-evolution-in-one-handy-figure/">150 Million Years of Fish Evolution in One Handy Figure</a> <i>ScientificAmerican</i>, 29 August 2013.</li> <li><a href="http://www.ageoffishes.org.au/index.html">Age Of Fishes Museum</a> <a href="https://web.archive.org/web/20200117130624/http://www.ageoffishes.org.au/index.html">Archived</a> 17 January 2020 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a>, <a href="/facts/Canowindra/6aMqRkML">Canowindra</a> - a permanent exhibition some of the best of the thousands of fossils dating from the Devonian Period found nearby.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Dawkins, Richard (2004). The Ancestor's Tale: A Pilgrimage to the Dawn of Life. Boston: Houghton Mifflin Company. p. 357. ISBN 978-0-618-00583-3. <a href="978-0-618-00583-3" target="_blank">978-0-618-00583-3</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Shu, D-G.; Luo, H-L.; Conway Morris, S.; Zhang, X-L.; Hu, S-X.; et al. (4 November 1999). "Lower Cambrian vertebrates from south China". Nature. 402 (6757): 42–46. Bibcode:1999Natur.402...42S. doi:10.1038/46965. S2CID 4402854. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Dawkins, Richard (2004). The Ancestor's Tale: A Pilgrimage to the Dawn of Life. Boston: Houghton Mifflin Company. p. 357. ISBN 978-0-618-00583-3. <a href="978-0-618-00583-3" target="_blank">978-0-618-00583-3</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Waggoner, Ben. "Vertebrates: Fossil Record". UCMP. Archived from the original on 29 June 2011. 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