Editing Teleost (section)

== Anatomy ==

{{main|Fish anatomy|Fish jaw}}

[[File:FishKeyDay.jpg|thumb|left|Teleost skull and jaw anatomy enables them both to suck in prey, and to close the mouth without expelling the prey again.<ref name="Benton"/>]]

[[Synapomorphy|Distinguishing]] features of the teleosts are mobile [[premaxilla]], elongated [[neural arch]]es at the end of the [[caudal fin]] and unpaired [[Branchial arch#Components|basibranchial]] toothplates.<ref>{{cite journal |last1=Patterson |first1=C. |last2=Rosen |first2=D. E. |year=1977 |title=Review of ichthyodectiform and other Mesozoic teleost fishes, and the theory and practice of classifying fossils |journal=[[Bulletin of the American Museum of Natural History]] |volume=158 |issue=2 |pages=81–172 |hdl=2246/1224}}</ref> The premaxilla is unattached to the [[neurocranium]] (braincase); it plays a role in protruding the mouth and creating a circular opening. This lowers the pressure inside the mouth, sucking the prey inside. The lower jaw and [[maxilla]] are then pulled back to close the mouth, and the fish [[Aquatic feeding mechanisms|is able to grasp the prey]]. By contrast, mere closure of the jaws would risk pushing food out of the mouth. In more advanced teleosts, the premaxilla is enlarged and has teeth, while the maxilla is toothless. The maxilla functions to push both the premaxilla and the lower jaw forward. To open the mouth, an [[muscle|adductor muscle]] pulls back the top of the maxilla, pushing the lower jaw forward. In addition, the maxilla rotates slightly, which pushes forward a bony process that interlocks with the premaxilla.<ref name="Benton">{{cite book |last=Benton |first=Michael |title=Vertebrate Palaeontology |chapter-url=https://books.google.com/books?id=VThUUUtM8A4C&pg=PA175 |year=2005 |publisher=[[John Wiley & Sons]] |edition=3rd |chapter=The Evolution of Fishes After the Devonian |isbn=978-1-4051-4449-0 |pages=175–184}}</ref>

[[File:FMIB 52170 Homocercal tail of a Flounder, Paralichthys californicus.jpeg|thumb|upright|Caudal skeleton showing symmetrical ([[homocercal]]) tail]]

The [[pharyngeal jaw]]s of teleosts, a second set of jaws contained within the throat, are composed of five [[pharyngeal arch|branchial arches]], loops of bone which support the [[gill]]s. The first three arches include a single basibranchial surrounded by two hypobranchials, ceratobranchials, epibranchials and pharyngobranchials. The median basibranchial is covered by a toothplate. The fourth arch is composed of pairs of ceratobranchials and epibranchials, and sometimes additionally, some pharyngobranchials and a basibranchial. The base of the lower pharyngeal jaws is formed by the fifth ceratobranchials while the second, third and fourth pharyngobranchials create the base of the upper. In the more [[basal (phylogenetics)|basal]] teleosts the pharyngeal jaws consist of well-separated thin parts that attach to the neurocranium, [[pectoral girdle]], and [[hyoid bone|hyoid bar]]. Their function is limited to merely transporting food, and they rely mostly on lower pharyngeal jaw activity. In more derived teleosts the jaws are more powerful, with left and right ceratobranchials fusing to become one lower jaw; the pharyngobranchials fuse to create a large upper jaw that articulates with the neurocranium. They have also developed a muscle that allows the pharyngeal jaws to have a role in grinding food in addition to transporting it.<ref name="teeth">{{cite journal |author1=Vandewalle, P. |author2=Parmentier, E. |author3=Chardon, M. |year=2000 |title=The branchial basket in Teleost feeding |journal=Cybium |volume=24 |issue=4 |pages=319–342 |url=http://www.vliz.be/imisdocs/publications/237770.pdf}}</ref>

The caudal fin is [[Fish anatomy#Fins|homocercal]], meaning the upper and lower lobes are about equal in size. The spine ends at the caudal peduncle, the base of the caudal fin, distinguishing this group from those in which the spine extends into the upper lobe of the caudal fin, such as most fish from the [[Paleozoic]] (541 to 252 million years ago). The neural arches are elongated to form uroneurals which provide support for this upper lobe.<ref name=Benton/>

Teleosts tend to be quicker and more flexible than more basal bony fishes. Their skeletal structure has evolved towards greater lightness. While teleost bones are well [[calcification|calcified]], they are constructed from a scaffolding of struts, rather than the dense [[cancellous bone]]s of [[Holostei|holostean]] fish. In addition, the lower jaw of the teleost is reduced to just three bones; the [[dentary]], the [[angular bone]] and the [[articular bone]].<ref>{{cite book |last1=Bone |first1=Q. |last2=Moore |first2=R. |year=2008 |title=Biology of Fishes |publisher=[[Garland Science]]|page=29 |isbn=978-0-415-37562-7}}</ref> The [[Reproductive system|genital]] and [[Urination|urinary tract]]s end behind the [[anus]] in the [[genital papilla]]; this is observed to [[Sexing|sex]] teleosts.<ref name="Jamieson2019">{{cite book |last=Jamieson |first=Barrie G. M. |title=Reproductive Biology and Phylogeny of Fishes, Vol 8B: Part B: Sperm Competition Hormones |url=https://books.google.com/books?id=nlivDwAAQBAJ&q=%22genital+papilla%22 |date=12 September 2019 |publisher=CRC Press |isbn=978-1-4398-4358-1}}</ref>