Editing Snake (section)

=== Fossils ===
There is fossil evidence to suggest that snakes may have evolved from burrowing lizards during the [[Cretaceous|Cretaceous Period]].<ref>{{cite journal |last1=Yi |first1=Hongyu |last2=Norell |first2=Mark A. |title=The burrowing origin of modern snakes |journal=[[Science Advances]] |year=2015 |volume=1 |issue=10 |pages=e1500743 |doi=10.1126/sciadv.1500743 |pmid=26702436 |pmc=4681343 |bibcode=2015SciA....1E0743Y |s2cid=8912706}}</ref><ref name="EB">{{Cite book |last=Mc Dowell |first=Samuel |title=Evolutionary Biology |chapter=The Evolution of the Tongue of Snakes, and its Bearing on Snake Origins |name-list-style=vanc |year=1972 |volume=6 |pages=191–273 |doi=10.1007/978-1-4684-9063-3_8 |isbn =978-1-4684-9065-7}}</ref> An early fossil snake relative, ''[[Najash rionegrina]]'', was a two-legged burrowing animal with a [[sacrum]], and was fully [[Terrestrial animal|terrestrial]].<ref name=najash>{{cite journal |vauthors=Apesteguía S, Zaher H |title=A Cretaceous terrestrial snake with robust hindlimbs and a sacrum |journal=[[Nature (journal)|Nature]] |volume=440 |issue=7087 |pages=1037–40 |date=April 2006 |pmid=16625194 |doi=10.1038/nature04413 |url=http://www.nature.com/nature/journal/v440/n7087/edsumm/e060420-11.html |url-status=live |archive-url=https://web.archive.org/web/20071218045427/http://www.nature.com/nature/journal/v440/n7087/edsumm/e060420-11.html |bibcode=2006Natur.440.1037A |s2cid=4417196 |archive-date=December 18, 2007}}</ref> ''Najash'', which lived 95 million years ago, also had a skull with several features typical for lizards, but had evolved some of the mobile skull joints that define the flexible skull in most modern snakes. The species did not show any resemblances to the modern burrowing blind snakes, which have often been seen as the most primitive group of extant forms.<ref>{{Cite web |url=https://theconversation.com/extraordinary-skull-fossil-reveals-secrets-of-snake-evolution-127307 |title=Extraordinary skull fossil reveals secrets of snake evolution |date=20 November 2019 |access-date=24 February 2024 |archive-date=24 February 2024 |archive-url=https://web.archive.org/web/20240224202530/https://theconversation.com/extraordinary-skull-fossil-reveals-secrets-of-snake-evolution-127307 |url-status=live }}</ref> One [[extant taxon|extant]] analog of these putative ancestors is the earless monitor ''[[Lanthanotidae|Lanthanotus]]'' of [[Borneo]] (though it is also [[Aquatic animal|semiaquatic]]).<ref name="M2">{{Cite journal |last=Mertens |first=Robert |name-list-style=vanc |title=Lanthanotus: an important lizard in evolution |journal=Sarawak Museum Journal |year=1961 |volume=10 |pages=320–322}}</ref> [[wikt:subterranean|Subterranean]] species evolved bodies streamlined for burrowing, and eventually lost their limbs.<ref name="M2"/> According to this hypothesis, features such as the [[Transparency (optics)|transparent]], fused eyelids ([[brille]]) and loss of external ears evolved to cope with [[fossorial]] difficulties, such as scratched [[cornea]]s and dirt in the ears.<ref name="EB"/><ref name="M2"/> Some primitive snakes are known to have possessed hindlimbs, but their pelvic bones lacked a direct connection to the vertebrae. These include fossil species like ''[[Haasiophis]]'', ''[[Pachyrhachis]]'' and ''[[Eupodophis]]'', which are slightly older than ''[[Najash]]''.<ref name="legs">{{cite web |title=New Fossil Snake With Legs |work=UNEP WCMC Database |publisher=[[American Association for the Advancement of Science]] |location=Washington, D.C. |url=http://www.wildlifenews.co.uk/articles2000/march/march2500a.htm |access-date=November 29, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20071225225126/http://www.wildlifenews.co.uk/articles2000/march/march2500a.htm |archive-date=December 25, 2007}}
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This hypothesis was strengthened in 2015 by the discovery of a 113-million-year-old fossil of a four-legged snake in Brazil that has been named ''[[Tetrapodophis|Tetrapodophis amplectus]]''. It has many snake-like features, is adapted for burrowing and its stomach indicates that it was preying on other animals.<ref>{{cite web |title=Four-legged snake ancestor 'dug burrows' |url=https://www.bbc.co.uk/news/science-environment-33621491 |first=Webb |last=Jonathan |name-list-style=vanc |date=July 24, 2014 |publisher=[[BBC|BBC Science & Environment]] |access-date=Jul 24, 2015 |url-status=live|archive-url=https://web.archive.org/web/20150726051600/http://www.bbc.co.uk/news/science-environment-33621491 |archive-date=July 26, 2015}}</ref> It is currently uncertain if ''Tetrapodophis'' is a snake or another species, in the [[Squamata|squamate]] order, as a snake-like body has independently evolved at least 26 times. ''Tetrapodophis'' does not have distinctive snake features in its spine and skull.<ref>{{cite web |title=A Fossil Snake With Four Legs |website=[[National Geographic]] |url=http://phenomena.nationalgeographic.com/2015/07/23/a-fossil-snake-with-four-legs/ |access-date=July 24, 2015 |first=Ed |last=Yong |name-list-style=vanc |url-status=dead |archive-url=https://web.archive.org/web/20150723221358/http://phenomena.nationalgeographic.com/2015/07/23/a-fossil-snake-with-four-legs/ |archive-date=July 23, 2015 |date=July 23, 2015}}</ref><ref>{{cite journal |vauthors=Martill DM, Tischlinger H, Longrich NR |title=EVOLUTION. A four-legged snake from the Early Cretaceous of Gondwana |journal=[[Science (journal)|Science]] |volume=349 |issue=6246 |pages=416–9 |date=July 2015 |pmid=26206932 |doi=10.1126/science.aaa9208 |url=https://researchportal.port.ac.uk/portal/en/publications/a-fourlegged-snake-from-the-early-cretaceous-of-gondwana(b6583c89-da01-4b9a-9f1e-dc142b9331ff).html |bibcode=2015Sci...349..416M |s2cid=25822461 |access-date=20 March 2020 |archive-date=2 August 2021 |archive-url=https://web.archive.org/web/20210802182407/https://researchportal.port.ac.uk/portal/en/publications/a-fourlegged-snake-from-the-early-cretaceous-of-gondwana(b6583c89-da01-4b9a-9f1e-dc142b9331ff).html |url-status=live }}</ref> A study in 2021 places the animal in a group of extinct marine lizards from the Cretaceous period known as [[Dolichosaurus|dolichosaur]]s and not directly related to snakes.<ref>{{Cite web |title=Famous Discovery of Four-Legged Snake Fossil Turns Out to Have a Twist in The Tale |url=https://www.msn.com/en-us/news/technology/famous-discovery-of-four-legged-snake-fossil-turns-out-to-have-a-twist-in-the-tale/ar-AAQQeEM?ocid=msedgdhp&pc=U531#comments |access-date=November 18, 2021 |website=www.msn.com |language=en-US |archive-date=18 November 2021 |archive-url=https://web.archive.org/web/20211118231312/https://www.msn.com/en-us/news/technology/famous-discovery-of-four-legged-snake-fossil-turns-out-to-have-a-twist-in-the-tale/ar-AAQQeEM?ocid=msedgdhp&pc=U531#comments |url-status=live }}</ref>

An alternative hypothesis, based on [[Morphology (biology)|morphology]], suggests the ancestors of snakes were related to [[mosasaur]]s—extinct [[aquatic animal|aquatic]] reptiles from the [[Cretaceous]]—forming the clade [[Pythonomorpha]].<ref name="Sanchez"/> According to this hypothesis, the fused, transparent eyelids of snakes are thought to have evolved to combat marine conditions (corneal water loss through osmosis), and the external ears were lost through disuse in an aquatic environment. This ultimately led to an animal similar to today's [[sea snake]]s. In the Late [[Cretaceous]], snakes recolonized land, and continued to diversify into today's snakes. Fossilized snake remains are known from early Late Cretaceous marine sediments, which is consistent with this hypothesis; particularly so, as they are older than the terrestrial ''Najash rionegrina''. Similar skull structure, reduced or absent limbs, and other anatomical features found in both mosasaurs and snakes lead to a positive [[Cladistics|cladistical]] correlation, although some of these features are shared with varanids.{{citation needed|date=June 2016}}

Genetic studies in recent years have indicated snakes are not as closely related to monitor lizards as was once believed—and therefore not to mosasaurs, the proposed ancestor in the aquatic scenario of their evolution. However, more evidence links mosasaurs to snakes than to varanids. Fragmented remains found from the [[Jurassic]] and Early Cretaceous indicate deeper fossil records for these groups, which may potentially refute either hypothesis.<ref>{{cite journal |vauthors=Vidal N, Hedges SB |title=Molecular evidence for a terrestrial origin of snakes |journal=[[Proceedings. Biological Sciences]] |volume=271 |issue=Suppl 4 |pages=S226-9 |date=May 2004 |pmid=15252991 |pmc=1810015 |doi=10.1098/rsbl.2003.0151}}</ref><ref>{{cite journal |vauthors=Caldwell MW, Nydam RL, Palci A, Apesteguía S |title=The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution |journal=[[Nature Communications]] |volume=6 |issue=1 |pages=5996 |date=January 2015 |pmid=25625704 |doi=10.1038/ncomms6996 |bibcode=2015NatCo...6.5996C |doi-access=free|hdl=11336/37995 |hdl-access=free }}</ref>

<gallery>
File:Tetrapodophis amplectus 3483.jpg|''[[Tetrapodophis]]''
File:Eupodophis at Royal Belgian Institute of Natural Sciences, Brussels.jpg|''[[Eupodophis descouensi]]''
File:Eupodophis descouensi Holotype.jpg|''[[Eupodophis descouensi]]''
File:Eupodophis descouensi Holotype hind leg.jpg|''[[Eupodophis]] descouensi'' hind leg
</gallery>