Editing Tuatara (section)

==== Parietal eye (third eye) ====
Like some other living vertebrates, including some lizards, the tuatara has a third eye on the top of its head called the [[parietal eye]] (also called a pineal or third eye) formed by the parapineal organ, with an accompanying opening in the skull roof called the pineal or parietal foramen, enclosed by the [[parietal bone]]s.<ref name=":1">{{Cite journal |last1=Smith |first1=Krister T. |last2=Bhullar |first2=Bhart-Anjan S. |last3=Köhler |first3=Gunther |last4=Habersetzer |first4=Jörg |date=April 2018 |title=The Only Known Jawed Vertebrate with Four Eyes and the Bauplan of the Pineal Complex |journal=Current Biology |volume=28 |issue=7 |pages=1101–1107.e2 |doi=10.1016/j.cub.2018.02.021 |issn=0960-9822|doi-access=free |pmid=29614279 |bibcode=2018CBio...28E1101S }}</ref> It has its own lens, a parietal plug which resembles a [[cornea]],<ref>{{cite journal |author1=Schwab, I.R. |author2=O'Connor, G.R. |date=March 2005 |title=The lonely eye |journal=The British Journal of Ophthalmology |volume=89 |issue=3 |pages=256 |doi=10.1136/bjo.2004.059105 |pmc=1772576 |pmid=15751188}}</ref> [[retina]] with rod-like structures, and degenerated nerve connection to the brain. The parietal eye is visible only in hatchlings, which have a translucent patch at the top centre of the skull. After four to six months, it becomes covered with opaque scales and pigment.<ref name="encyclo" /> While capable of detecting light, it is probably not capable of detecting movement or forming an image.<ref>{{Cite journal |last=Jones |first=Marc E.H. |last2=Cree |first2=Alison |date=December 2012 |title=Tuatara |url=https://linkinghub.elsevier.com/retrieve/pii/S0960982212013036 |journal=Current Biology |language=en |volume=22 |issue=23 |pages=R986–R987 |doi=10.1016/j.cub.2012.10.049}}</ref> It likely serves to regulate the [[circadian rhythm]] and possibly detect seasonal changes, and help with [[thermoregulation]].<ref name="encyclo" /><ref name=":1" />

Of all extant tetrapods, the parietal eye is most pronounced in the tuatara. It is part of the pineal complex, another part of which is the [[pineal gland]], which in tuatara secretes melatonin at night.<ref name="encyclo" /> Some [[salamander]]s have been shown to use their pineal bodies to perceive polarised light, and thus determine the position of the sun, even under cloud cover, aiding [[Animal navigation|navigation]].<ref>{{cite book |author=Halliday, T.R. |year=2002 |chapter=Salamanders and newts: Finding breeding ponds |editor1=Halliday, T. |editor2=Adler, K. |title=The New Encyclopedia of Reptiles and Amphibians |place=Oxford, UK |publisher=Oxford University Press |isbn=0-19-852507-9|page=52}}</ref>