Editing Reptile (section)

===Reproduction===
[[File:Crocodile Egg Diagram.svg|thumb|Crocodilian egg diagram<br/>
(1)&nbsp;eggshell, (2)&nbsp;yolk sac, (3)&nbsp;yolk (nutrients), (4)&nbsp;vessels, (5)&nbsp;[[amnion]], (6)&nbsp;[[chorion]], (7)&nbsp;air space, (8)&nbsp;[[allantois]], (9)&nbsp;albumin (egg white), (10)&nbsp;amniotic sac, (11)&nbsp;crocodile embryo, (12)&nbsp;amniotic fluid]]
[[File:Hemidactylus_frenatus_mating,_ventral_view.jpg|thumb|[[Common house gecko]]s mating, ventral view with [[hemipenis]] inserted in the [[cloaca]]]]
[[File:Trachylepis maculilabris mating.jpg|thumb|Most reptiles reproduce sexually, for example this ''Trachylepis maculilabris'' [[skink]]]]
[[File:Tortoise-Hatchling.jpg|thumb|Reptiles have [[amniote|amniotic]] eggs with hard or leathery shells, requiring [[internal fertilization]] when mating.]]

Reptiles generally [[sexual reproduction|reproduce sexually]],<ref>{{cite journal |title=Male reproductive behaviour of ''Naja oxiana'' {{small|(Eichwald, 1831)}} in captivity, with a case of unilateral hemipenile prolapse |year=2018 |journal=Herpetology Notes |url=https://www.researchgate.net/publication/335270872}}</ref> though some are capable of [[asexual reproduction]]. All reproductive activity occurs through the [[cloaca]], the single exit/entrance at the base of the tail where waste is also eliminated. Most reptiles have [[copulatory organ]]s, which are usually retracted or inverted and stored inside the body. In turtles and crocodilians, the male has a single median [[penis]], while squamates, including snakes and lizards, possess a pair of [[hemipenis|hemipenes]], only one of which is typically used in each session. Tuatara, however, lack copulatory organs, and so the male and female simply press their cloacas together as the male discharges sperm.<ref>{{cite book |author=Lutz, Dick |year=2005 |title=Tuatara: A living fossil |place=Salem, OR |publisher=DIMI Press |isbn=978-0-931625-43-5}}</ref>

Most reptiles lay amniotic eggs covered with leathery or calcareous shells. An [[amnion]]&nbsp;(5), [[chorion]]&nbsp;(6), and [[allantois]]&nbsp;(8) are present during [[embryo]]nic life. The eggshell&nbsp;(1) protects the crocodile embryo&nbsp;(11) and keeps it from drying out, but it is flexible to allow gas exchange. The chorion&nbsp;(6) aids in gas exchange between the inside and outside of the egg. It allows carbon dioxide to exit the egg and oxygen gas to enter the egg. The albumin&nbsp;(9) further protects the embryo and serves as a reservoir for water and protein. The allantois&nbsp;(8) is a sac that collects the metabolic waste produced by the embryo. The amniotic sac&nbsp;(10) contains amniotic fluid&nbsp;(12) which protects and cushions the embryo. The amnion&nbsp;(5) aids in osmoregulation and serves as a saltwater reservoir. The yolk sac&nbsp;(2) surrounding the yolk&nbsp;(3) contains protein and fat rich nutrients that are absorbed by the embryo via vessels&nbsp;(4) that allow the embryo to grow and metabolize. The air space&nbsp;(7) provides the embryo with oxygen while it is hatching. This ensures that the embryo will not suffocate while it is hatching. There are no [[larva]]l stages of development. [[Viviparity]] and [[ovoviviparity]] have evolved in squamates and many extinct clades of reptiles. Among squamates, many species, including all boas and most vipers, use this mode of reproduction. The degree of viviparity varies; some species simply retain the eggs until just before hatching, others provide maternal nourishment to supplement the yolk, and yet others lack any yolk and provide all nutrients via a structure similar to the mammalian [[placenta]]. The earliest documented case of viviparity in reptiles is the Early [[Permian]] [[mesosaur]]s,<ref name=PFML12>{{cite journal |author1=Piñeiro, G. |author2=Ferigolo, J. |author3=Meneghel, M. |author4=Laurin, M. |year=2012 |title=The oldest known amniotic embryos suggest viviparity in mesosaurs |journal=Historical Biology |volume=24 |issue=6 |pages=620–630 |s2cid=59475679 |doi=10.1080/08912963.2012.662230 |bibcode=2012HBio...24..620P }}</ref> although some individuals or taxa in that clade may also have been oviparous because a putative isolated egg has also been found. Several groups of Mesozoic marine reptiles also exhibited viviparity, such as [[mosasaur]]s, [[ichthyosaur]]s, and [[Sauropterygia]], a group that includes [[pachypleurosaur]]s and [[Plesiosauria]].<ref name=S12/>

Asexual reproduction has been identified in [[squamata|squamates]] in six families of lizards and one snake. In some species of squamates, a population of females is able to produce a unisexual diploid clone of the mother. This form of asexual reproduction, called [[parthenogenesis]], occurs in several species of [[gecko]], and is particularly widespread in the [[teiidae|teiids]] (especially ''Aspidocelis'') and [[lacertidae|lacertids]] (''[[Lacerta (genus)|Lacerta]]''). In captivity, [[Komodo dragon]]s (Varanidae) have reproduced by [[parthenogenesis]].

Parthenogenetic species are suspected to occur among [[chameleon]]s, [[agamidae|agamids]], [[night lizard|xantusiids]], and [[typhlopidae|typhlopids]].

Some reptiles exhibit [[temperature-dependent sex determination]] (TDSD), in which the incubation temperature determines whether a particular egg hatches as male or female. TDSD is most common in turtles and crocodiles, but also occurs in lizards and tuatara.<ref>{{cite book |title=FireFly Encyclopedia of Reptiles and Amphibians |year=2008 |publisher=Firefly Books Ltd |location=Richmond Hill, Ontario |isbn=978-1-55407-366-5 |pages=117–118 }}</ref> To date, there has been no confirmation of whether TDSD occurs in snakes.<ref>{{cite book |last1=Chadwick |first1=Derek |last2=Goode |first2=Jamie |year=2002 |title=The Genetics and Biology of Sex ... |publisher=John Wiley & Sons |isbn=978-0-470-84346-8 |url=https://books.google.com/books?id=lc5Bg-hmsBYC&q=temperature%20dependent%20sex%20determination%20snake&pg=PA101 |via=Google Books |access-date=March 16, 2010}}</ref>