Editing Snake (section)

=== Evolution ===
{{Unsolved|biology|Did snakes evolve from burrowing lizards or aquatic lizards?}}
{{Cladogram|title=A family level phylogenetic overview of modern snakes.
|clades={{clade|style=font-size:88.888888%;line-height:100%
 |label1=Snakes
 |1={{clade
     |label1=[[Scolecophidia]]
     |1={{clade
         |1=[[Leptotyphlopidae]]
         |label2=
         |2={{clade
             |1=[[Gerrhopilidae]]
             |2={{clade
                |1=[[Typhlopidae]]
                |2=[[Xenophidiidae]]
                }}
            }}
        }}
     |label2=
     |2={{clade
      |label1=
      |1=[[Anomalepididae]]
      |label2=[[Alethinophidia]]
         |2={{clade
            |1={{clade
            |label1=
            |1={{clade
                 |1=[[Aniliidae]]
                 |2=[[Tropidophiidae]]
               }}
         |label2=
                 |2={{clade
                   |1={{clade
                      |1={{clade
                         |1={{clade
                            |1=[[Xenopeltidae]]}}
                            |2={{clade
                               |1=[[Loxocemidae]]
                               |2=[[Pythonidae]]}}
                           
                       }}
                      |2={{clade
                          |label1=
                             |1=[[Boidae]]
                          |label2=
                             |2={{clade
                                |1=[[Bolyeridae]]
                                |2=[[Xenophidiidae]]
                                }}
                          }}
                      }}
                 
                      |2={{clade
                          |label1=
                             |1=[[Uropeltidae]]
                          |label2=
                             |2={{clade
                                |1=[[Anomochilidae]]
                                |2=[[Cylindrophiidae]]
                                }}
                                }}
               }}
         }}
         |2={{clade
                                |1={{clade
                                   |1=[[Acrochordidae]]}}
                                |2={{clade
                                   |1={{clade
                                   |1=[[Xenodermidae]]}}
                                   |2={{clade
                                      |1={{clade
                                        |1=[[Pareidae]]}}
                                |2={{clade|1={{clade
                                |1=[[Viperidae]]}}
                                |2={{clade|1={{clade
                                |1=[[Homalopsidae]]}}
                                |2={{clade|1={{clade
                                |1=[[Colubridae]]}}
                                |2={{clade
                                |1=[[Lamprophiidae]]
                                |2=[[Elapidae]]}}}}}}}}}}}}
                                }}
      }}
     }}
     }}
|caption=Note: the tree only indicates relationships, not evolutionary branching times. This is not a definitive tree. It is the best that could be done as of 2024. See original paper for a discussion of difficulties.<ref name="ScienceArticle">{{cite journal |last1=Title |first1=Pascal O. |last2=Singhal |first2=Sonal |last3=Grundler |first3=Michael C. |last4=Costa |first4=Gabriel C. |last5=Pyron |first5=R. Alexander |last6=Colston |first6=Timothy J. |last7=Grundler |first7=Maggie R. |last8=Prates |first8=Ivan |last9=Stepanova |first9=Natasha |last10=Jones |first10=Marc E. H. |last11=Cavalcanti |first11=Lucas B. Q. |last12=Colli |first12=Guarino R. |last13=Di-Poï |first13=Nicolas |last14=Donnellan |first14=Stephen C. |last15=Moritz |first15=Craig |last16=Mesquita |first16=Daniel O. |last17=Pianka |first17=Eric R. |last18=Smith |first18=Stephen A. |last19=Vitt |first19=Laurie J. |last20=Rabosky |first20=Daniel L. |title=The macroevolutionary singularity of snakes |journal=Science |date=23 February 2024 |volume=383 |issue=6685 |pages=918–923 |doi=10.1126/science.adh2449 |pmid=38386744 |bibcode=2024Sci...383..918T |url=https://www.science.org |access-date=22 March 2024|url-access=subscription }}</ref>
}}
}}
The fossil record of snakes is relatively poor because snake [[skeleton]]s are typically small and fragile making [[fossil]]ization uncommon. Fossils readily identifiable as snakes (though often retaining hind limbs) first appear in the fossil record during the [[Cretaceous]] period.<ref>{{cite book |last=Durand |first=J.F. |date=2004 |title=The origin of snakes |series=Geoscience Africa |volume=Abstract |publisher=[[University of the Witwatersrand]] |location=Johannesburg, South Africa |page=187}}</ref> The earliest known true snake fossils (members of the crown group Serpentes) come from the marine [[Simoliophiidae|simoliophiid]]s, the oldest of which is the [[Late Cretaceous]] ([[Cenomanian]] age) ''[[Haasiophis terrasanctus]]'' from the [[West Bank]],<ref name=snake_origin_ecology>{{cite journal |vauthors=Hsiang AY, Field DJ, Webster TH, Behlke AD, Davis MB, Racicot RA, Gauthier JA |title=The origin of snakes: revealing the ecology, behavior, and evolutionary history of early snakes using genomics, phenomics, and the fossil record |journal=BMC Evolutionary Biology |volume=15 |pages=87 |date = May 2015 |issue=1 |pmid=25989795 |pmc=4438441 |doi=10.1186/s12862-015-0358-5 |bibcode=2015BMCEE..15...87H |doi-access=free }}</ref> dated to between 112 and 94 million years old.<ref name=timetree>{{cite book |last1=Vidal |first1=N. |last2=Rage |first2=J.-C. |last3=Couloux |first3=A. |last4=Hedges |first4=S.B. |date=2009 |chapter=Snakes (Serpentes) |pages=390–397 |editor1-last=Hedges |editor1-first=S. B. |editor2-last=Kumar |editor2-first=S. |title=The Timetree of Life |publisher=[[Oxford University Press]]}}</ref>

Based on genomic analysis it is certain that snakes descend from [[lizard]]s.<ref name="ScienceArticle"/> This conclusion is also supported by [[comparative anatomy]], and the fossil record.<ref name="Meh87">{{cite book |last=Mehrtens |first=J. M. |date=1987 |title=Living Snakes of the World in Color |location=New York |publisher=Sterling Publishers |isbn=0-8069-6460-X}}</ref>{{Rp|11}}<ref name="Sanchez">{{cite web |last=Sanchez |first=Alejandro |name-list-style=vanc |title=Diapsids III: Snakes |work=Father Sanchez's Web Site of West Indian Natural History |url=http://www.kingsnake.com/westindian/metazoa12.html |access-date=November 26, 2007|url-status=live |archive-url=https://web.archive.org/web/20071127163408/http://www.kingsnake.com/westindian/metazoa12.html |archive-date=November 27, 2007}}</ref><ref name="ScienceArticle"/>

[[Pythonidae|Python]]s and [[Boidae|boa]]s—primitive groups among modern snakes—have vestigial hind limbs: tiny, clawed digits known as [[anal spur]]s, which are used to grasp during mating.<ref name="Meh87"/>{{Rp|11}}<ref name="legs"/> The families [[Leptotyphlopidae]] and [[Typhlopidae]] also possess remnants of the pelvic girdle, appearing as horny projections when visible.

Front limbs are nonexistent in all known snakes. This is caused by the evolution of their [[Hox gene]]s, controlling limb [[morphogenesis]]. The axial skeleton of the snakes' common ancestor, like most other tetrapods, had regional specializations consisting of cervical (neck), thoracic (chest), lumbar (lower back), sacral (pelvic), and caudal (tail) vertebrae. Early in snake evolution, the Hox gene expression in the axial skeleton responsible for the development of the thorax became dominant. As a result, the vertebrae anterior to the hindlimb buds (when present) all have the same thoracic-like identity (except from the [[Atlas (anatomy)|atlas]], [[Axis (anatomy)|axis]], and 1–3 neck vertebrae). In other words, most of a snake's skeleton is an extremely extended thorax. Ribs are found exclusively on the thoracic vertebrae. Neck, lumbar and pelvic vertebrae are very reduced in number (only 2–10 lumbar and pelvic vertebrae are present), while only a short tail remains of the caudal vertebrae. However, the tail is still long enough to be of important use in many species, and is modified in some aquatic and tree-dwelling species.{{Citation needed|date=November 2024}}

Many modern snake groups originated during the [[Paleocene]], alongside the [[adaptive radiation]] of mammals following the extinction of (non-avian) [[dinosaur]]s. The expansion of grasslands in North America also led to an explosive radiation among snakes.<ref name="Fossil Snakes of North America">{{cite book |last1=Holman |first1=J. Alan |name-list-style=vanc |title=Fossil Snakes of North America |date=2000 |publisher=[[Indiana University Press]] |location=Bloomington, IN |isbn=978-0253337214 |pages=284–323 |edition=First}}</ref> Previously, snakes were a minor component of the North American fauna, but during the Miocene, the number of species and their prevalence increased dramatically with the first appearances of [[viper]]s and [[elapid]]s in North America and the significant diversification of [[Colubridae]] (including the origin of many modern genera such as ''[[Nerodia]]'', ''[[Lampropeltis]]'', ''[[Pituophis]]'', and ''[[Pantherophis]]'').<ref name="Fossil Snakes of North America"/>