Editing Tetrapod (section)

==== Vision ====
Changes in the eye came about because the behavior of light at the surface of the eye differs between an air and water environment due to the difference in [[refractive index]], so the [[focal length]] of the [[lens (anatomy)|lens]] altered to function in air. The [[eye]] was now exposed to a relatively dry environment rather than being bathed by water, so [[eyelid]]s developed and [[tear duct]]s evolved to produce a liquid to moisten the eyeball.

Early tetrapods inherited a set of five [[rod cell|rod]] and [[cone cell|cone]] opsins known as the vertebrate [[opsin]]s.<ref name="HuntHankins2014">{{cite book|author1=David M. Hunt|author2=Mark W. Hankins|author3=Shaun P Collin|author4=N. Justin Marshall|title=Evolution of Visual and Non-visual Pigments|url=https://books.google.com/books?id=APWwBAAAQBAJ&pg=PA165|date=4 October 2014|publisher=Springer|isbn=978-1-4614-4355-1|pages=165–|access-date=13 March 2016|archive-date=18 August 2020|archive-url=https://web.archive.org/web/20200818220721/https://books.google.com/books?id=APWwBAAAQBAJ&pg=PA165|url-status=live}}</ref><ref name="StavengaGrip2000">{{cite book|last1=Stavenga|first1=D.G.|last2=de Grip|first2=W.J.|last3=Pugh|first3=E.N.|title=Molecular Mechanisms in Visual Transduction|url=https://books.google.com/books?id=ZbWim1qiifgC&pg=PA269|access-date=14 June 2015|date=30 November 2000|publisher=Elsevier|isbn=978-0-08-053677-4|page=269|archive-date=20 August 2020|archive-url=https://web.archive.org/web/20200820040132/https://books.google.com/books?id=ZbWim1qiifgC&pg=PA269|url-status=live}}</ref><ref name="LazarevaShimizu2012">{{cite book|last1=Lazareva|first1=Olga F.|last2=Shimizu|first2=Toru|author3=Edward A. Wasserman|author-link3=Edward Wasserman|title=How Animals See the World: Comparative Behavior, Biology, and Evolution of Vision|url=https://books.google.com/books?id=KOv6cHWdjG8C&pg=PA459|access-date=14 June 2015|date=19 April 2012|publisher=OUP USA|isbn=978-0-19-533465-4|page=459|archive-date=19 August 2020|archive-url=https://web.archive.org/web/20200819135654/https://books.google.com/books?id=KOv6cHWdjG8C&pg=PA459|url-status=live}}</ref>

Four cone opsins were present in the first vertebrate, inherited from invertebrate ancestors:

*[[OPN1LW|LWS]]/[[OPN1MW|MWS]] (long- to medium-wave sensitive) - green, yellow, or red 
*[[OPN1SW|SWS1]] (short-wave sensitive) - ultraviolet or violet - lost in monotremes (platypus, echidna)
*SWS2 (short-wave sensitive) - violet or blue - lost in therians (placental mammals and marsupials)
*RH2 (rhodopsin-like cone opsin) - green - lost separately in amphibians and mammals, retained in reptiles and birds

A single rod opsin, rhodopsin, was present in the first jawed vertebrate, inherited from a jawless vertebrate ancestor:

*[[rhodopsin|RH1]] (rhodopsin) - blue-green - used night vision and color correction in low-light environments