Lyson, Tyler R.; Schachner, Emma R.; Botha-Brink, Jennifer; Scheyer, Torsten M.; Lambertz, Markus; Bever, G.S.; Rubidge, Bruce S.; de Queiroz, Kevin (2014). "Origin of the unique ventilatory apparatus of turtles" (PDF). Nature Communications. 5 (5211): 5211. Bibcode: 2014NatCo...5.5211L. doi: 10.1038/ncomms6211. PMID 25376734. a b Katsu, Y.; Braun, E.L.; Guillette, L.J. Jr.; Iguchi, T. (2010-03-17). "From reptilian phylogenomics to reptilian genomes: analyses of c-Jun and DJ-1 proto-oncogenes". Cytogenetic and Genome Research. 127 (2–4): 79–93. doi: 10.1159/000297715. PMID 20234127. S2CID 12116018. Only three reptile species, including the yellow-bellied three-toed skink of Australia, actually combine both eggs and live birthing methods (the rarity suggests that evolution probably does not favor this in-between stage). The skink’s offspring begins life encased in an egg, the same as any other reptile. But as the embryo develops, the egg begins to thin out until all that’s left upon its birth is a small membrane. The main problem with this method is that the thin egg shells don’t contain enough calcium to nourish the offspring. The mothers appear to compensate for this by secreting calcium from the uterus so it can be absorbed by the developing embryo. The evidence suggests that the skink can choose to lay eggs a few weeks early if it seems like there’s less danger to the offspring. In harsher climates, the mother will keep the offspring insider her body for longer to protect them.

Reptiles shed their skin through a process called ecdysis which occurs continuously throughout their lifetime. In particular, younger reptiles tend to shed once every 5–6 weeks while adults shed 3–4 times a year. [96] Younger reptiles shed more because of their rapid growth rate. Once full size, the frequency of shedding drastically decreases. The process of ecdysis involves forming a new layer of skin under the old one. Proteolytic enzymes and lymphatic fluid is secreted between the old and new layers of skin. Consequently, this lifts the old skin from the new one allowing shedding to occur. [97] Snakes will shed from the head to the tail while lizards shed in a "patchy pattern". [97] Dysecdysis, a common skin disease in snakes and lizards, will occur when ecdysis, or shedding, fails. [98] There are numerous reasons why shedding fails and can be related to inadequate humidity and temperature, nutritional deficiencies, dehydration and traumatic injuries. [97] Nutritional deficiencies decrease proteolytic enzymes while dehydration reduces lymphatic fluids to separate the skin layers. Traumatic injuries on the other hand, form scars that will not allow new scales to form and disrupt the process of ecdysis. [98] Excretion [ edit ] Chiari, Ylenia; Cahais, Vincent; Galtier, Nicolas; Delsuc, Frédéric (2012). "Phylogenomic analyses support the position of turtles as the sister group of birds and crocodiles (Archosauria)". BMC Biology. 10 (65): 65. doi: 10.1186/1741-7007-10-65. PMC 3473239. PMID 22839781. Crocodiles are protected in many parts of the world, and are farmed commercially. Their hides are tanned and used to make leather goods such as shoes and handbags; crocodile meat is also considered a delicacy. [166] The most commonly farmed species are the saltwater and Nile crocodiles. Farming has resulted in an increase in the saltwater crocodile population in Australia, as eggs are usually harvested from the wild, so landowners have an incentive to conserve their habitat. Crocodile leather is made into wallets, briefcases, purses, handbags, belts, hats, and shoes. Crocodile oil has been used for various purposes. [167] Huey, R.B. (1982): Temperature, physiology, and the ecology of reptiles. Side 25–91. In Gans, C. & Pough, F.H. (red), Biology of the Reptili No. 12, Physiology (C). Academic Press, London. artikkela b Thorpe, Roger S.; Thorpe, R. S.;Wüster, Wolfgang & Malhotra, Anita (1997). Venomous snakes: ecology, evolution, and snakebite. Vol. 70 of Symposia of the Zoological Society of London. Oxford University Press, London. ISBN 0-19-854986-5. Young Snake Rattles! Ask a scientist! (Zoology archive). Newton BBS, Argonne National Laboratory. Newton.dep.anl.gov. Retrieved on 2013-01-21. Main article: Reptiles in culture Painting of fighting " Laelaps" (now Dryptosaurus) by Charles R. Knight (1897) After the extinction of most archosaur and marine reptile lines by the end of the Cretaceous, reptile diversification continued throughout the Cenozoic. Squamates took a massive hit during the K–Pg event, only recovering ten million years after it, [62] but they underwent a great radiation event once they recovered, and today squamates make up the majority of living reptiles (> 95%). [63] [64] Approximately 10,000 extant species of traditional reptiles are known, with birds adding about 10,000 more, almost twice the number of mammals, represented by about 5,700living species (excluding domesticated species). [65] Snakes have smaller scales around the mouth and sides of the body which allow expansion so that a snake can consume prey of much larger width than itself. Snake scales are made of keratin, the same material that hair and fingernails are made of. [9] They are cool and dry to touch. [10] Surface and shape [ edit ]

See also: Skull roof Reptiles, from Nouveau Larousse Illustré, 1897–1904, notice the inclusion of amphibians (below the crocodiles) Parthenogenetic species are suspected to occur among chameleons, agamids, xantusiids, and typhlopids. Divers, Stephen J.; Mader, Douglas R. (2005). Reptile Medicine and Surgery. Amsterdam: Elsevier Health Sciences. pp.481, 597. ISBN 9781416064770. Regular shedding – Reptiles shed their skin continuously throughout their lifetimes. Shedding tends to be the most frequent during the adolescent phase, because the skin doesn’t actually grow in proportion with the body. The frequency of the shedding tends to decrease once the reptile reaches adulthood. At that point it’s mostly shed to maintain good health.There is no simple way of differentiating a venomous snake from a non-venomous one merely by using a scale character. Finding out whether a snake is venomous or not is correctly done by identification of the species of a snake with the help of experts, [31] :190 or in their absence, close examination of the snake and using authoritative references on the snakes of the particular geographical region to identify it. Scale patterns help to indicate the species and from the references, it can be verified if the snake species is known to be venomous or not. Early in the period, the modern reptiles, or crown-group reptiles, evolved and split into two main lineages: the Archosauromorpha (forebears of turtles, crocodiles, and dinosaurs) and the Lepidosauromorpha (predecessors of modern lizards and tuataras). Both groups remained lizard-like and relatively small and inconspicuous during the Permian. Gray, Brian S. (2005) The Serpent's Cast: A Guide to the Identification of shed skins from snakes of the Northeast and Mid-Atlantic States. The Center for North American Herpetology Monograph Series no. 1.Serpent's Tale Natural History Book Distributors, Lanesboro, Minnesota. Snakeskin, with its highly periodic cross-hatch or grid patterns, appeals to people's aesthetics and have been used to manufacture many leather articles including fashionable accessories. [34] The use of snakeskin has however endangered snake populations [35] and resulted in international restrictions in trade of certain snake species and populations in the form of CITES provisions. [36] Animal lovers in many countries now promote the use of artificial snakeskin instead, which are easily produced from embossed leather, patterned fabric, plastics and other materials. [34]