Editing Teleost (section)

=== Evolutionary trends ===

[[File:Aspidorhynchus acustirostris.jpg|thumb|upright|''[[Aspidorhynchus acustirostris]]'', an early teleost from the [[Middle Jurassic]]]]

The first fossils assignable to this diverse group appear in the [[Early Triassic]],<ref name="Clarke 2018">{{cite journal |last1=Clarke |first1=John T. |last2=Friedman |first2=Matt |date=August 2018 |title=Body-shape diversity in Triassic–Early Cretaceous neopterygian fishes: sustained holostean disparity and predominantly gradual increases in teleost phenotypic variety |journal=Paleobiology|volume=44|issue=3 |pages=402–433 |doi=10.1017/pab.2018.8 |bibcode=2018Pbio...44..402C |s2cid=90207334 |url=http://osf.io/2ytc5/}}</ref> after which teleosts accumulated novel body shapes predominantly gradually for the first 150 million years of their evolution ([[Early Triassic]] through [[early Cretaceous]]).<ref name="Clarke 2018"/>

The most basal of the living teleosts are the [[Elopomorpha]] (eels and allies) and the [[Osteoglossomorpha]] (elephantfishes and allies). There are 800 species of elopomorphs. They have thin leaf-shaped larvae known as [[leptocephalus|leptocephali]], specialised for a marine environment. Among the elopomorphs, eels have elongated bodies with lost pelvic girdles and ribs and fused elements in the upper jaw. The 200 species of osteoglossomorphs are defined by a bony element in the tongue. This element has a basibranchial behind it, and both structures have large teeth which are paired with the teeth on the parasphenoid in the roof of the mouth. The clade [[Otocephala]] includes the [[Clupeiformes]] (herrings) and [[Ostariophysi]] (carps, catfishes and allies). Clupeiformes consists of 350 living species of herring and herring-like fishes. This group is characterised by an unusual abdominal [[scute]] and a different arrangement of the hypurals. In most species, the swim bladder extends to the braincase and plays a role in hearing. Ostariophysi, which includes most freshwater fishes, includes species that have developed some unique adaptations.<ref name=Benton/> One is the [[Weberian apparatus]], an arrangement of bones (Weberian ossicles) connecting the swim bladder to the inner ear. This enhances their hearing, as sound waves make the bladder vibrate, and the bones transport the vibrations to the inner ear. They also have a [[Schreckstoff|chemical alarm system]]; when a fish is injured, the warning substance gets in the water, alarming nearby fish.<ref name=Helfman>Helfman, Collette, Facey and Bowen pp. 268–274</ref>

The majority of teleost species belong to the clade [[Euteleostei]], which consists of 17,419 species classified in 2,935 genera and 346 families. Shared traits of the euteleosts include similarities in the embryonic development of the bony or cartilaginous structures located between the head and dorsal fin (supraneural bones), an outgrowth on the stegural bone (a bone located near the neural arches of the tail), and caudal median cartilages located between hypurals of the caudal base. The majority of euteleosts are in the clade [[Neoteleostei]]. A derived trait of neoteleosts is a muscle that controls the pharyngeal jaws, giving them a role in grinding food. Within neoteleosts, members of the [[Acanthopterygii]] have a spiny dorsal fin which is in front of the soft-rayed dorsal fin.<ref>Helfman, Collette, Facey and Bowen pp. 274–276</ref> This fin helps provide thrust in locomotion<ref>{{cite journal |last1=Drucker |first1=E. G. |last2=Lauder |first2=G. V. |year=2001 |title=Locomotor function of the dorsal fin in teleost fishes: experimental analysis of wake forces in sunfish |journal=[[The Journal of Experimental Biology]] |volume=204 |issue=Pt 17 |pages=2943–2958 |doi=10.1242/jeb.204.17.2943 | pmid=11551984 |url=http://jeb.biologists.org/content/204/17/2943|url-access=subscription }}</ref> and may also play a role in defense. Acanthomorphs have developed spiny [[Fish scale#Ctenoid scales|ctenoid scales]] (as opposed to the [[Fish scale#Cycloid scales|cycloid scales]] of other groups), tooth-bearing premaxilla and greater adaptations to high speed swimming.<ref name=Benton/>

The [[adipose fin]], which is present in over 6,000 teleost species, is often thought to have evolved once in the lineage and to have been lost multiple times due to its limited function. A 2014 study challenges this idea and suggests that the adipose fin is an example of [[homoplasy|convergent evolution]]. In [[Characiformes]], the adipose fin develops from an outgrowth after the reduction of the larval fin fold, while in [[Salmoniformes]], the fin appears to be a remnant of the fold.<ref>{{cite journal |author1=Steward, T. A. |author2=Smith, W. L. |author3=Coates, M. I. |year=2014 |title=The origins of adipose fins: an analysis of homoplasy and the serial homology of vertebrate appendages |journal=[[Proceedings of the Royal Society|Proceedings of the Royal Society B]] |volume=281 |issue=1781 |doi=10.1098/rspb.2013.3120 |pmid=24598422 |pmc=3953844 |page=20133120}}</ref>