Editing Reptile (section)

===Metabolism===
[[File:Homeothermy-poikilothermy.png|thumb|right|Sustained energy output ([[joule]]s) of a typical reptile versus a similar size mammal as a function of core body temperature. The mammal has a much higher peak output, but can only function over a very narrow range of body temperature.]]

Modern non-avian reptiles exhibit some form of [[Ectotherm|cold-bloodedness]] (i.e. some mix of [[poikilotherm]]y, [[ectotherm]]y, and [[bradymetabolism]]) so that they have limited physiological means of keeping the body temperature constant and often rely on external sources of heat. Due to a less stable core temperature than [[bird]]s and [[mammal]]s, reptilian biochemistry requires [[enzyme]]s capable of maintaining efficiency over a greater range of temperatures than in the case for [[warm-blooded]] animals. The optimum body temperature range varies with species, but is typically below that of warm-blooded animals; for many lizards, it falls in the {{convert|24|–|35|C|F}} range,<ref>Huey, R.B. & Bennett, A.F. (1987):Phylogenetic studies of coadaptation: Preferred temperatures versus optimal performance temperatures of lizards. ''Evolution'' No. 4, vol 5: pp. 1098–1115 [http://faculty.washington.edu/hueyrb/pdfs/Coadaptation_Evolution.pdf PDF] {{Webarchive|url=https://web.archive.org/web/20220911080152/http://faculty.washington.edu/hueyrb/pdfs/Coadaptation_Evolution.pdf |date=2022-09-11 }}</ref> while extreme heat-adapted species, like the American [[desert iguana]] ''Dipsosaurus dorsalis'', can have optimal physiological temperatures in the mammalian range, between {{convert|35|and|40|C|F}}.<ref>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.[http://faculty.washington.edu/hueyrb/pdfs/temp_phys_ecol_rep_1982.pdf artikkel] {{Webarchive|url=https://web.archive.org/web/20220419174304/http://faculty.washington.edu/hueyrb/pdfs/temp_phys_ecol_rep_1982.pdf |date=2022-04-19 }}</ref> While the optimum temperature is often encountered when the animal is active, the low basal metabolism makes body temperature drop rapidly when the animal is inactive.

As in all animals, reptilian muscle action produces heat. In large reptiles, like [[leatherback turtle]]s, the low surface-to-volume ratio allows this metabolically produced heat to keep the animals warmer than their environment even though they do not have a [[warm-blooded]] metabolism.<ref>Spotila J.R. & Standora, E.A. (1985) Environmental constraints on the thermal energetics of sea turtles. ''Copeia'' 3: 694–702</ref> This form of homeothermy is called [[gigantothermy]]; it has been suggested as having been common in large [[dinosaur]]s and other extinct large-bodied reptiles.<ref>Paladino, F.V.; Spotila, J.R. & Dodson, P. (1999): A blueprint for giants: modeling the physiology of large dinosaurs. ''The Complete Dinosaur''. Bloomington, Indiana University Press. pp. 491–504. {{ISBN|978-0-253-21313-6}}.</ref><ref>{{cite journal | last1 = Spotila | first1 = J.R. | last2 = O'Connor | first2 = M.P. | last3 = Dodson | first3 = P. | last4 = Paladino | first4 = F.V. | year = 1991 | title = Hot and cold running dinosaurs: body size, metabolism and migration | journal = Modern Geology | volume = 16 | pages = 203–227 }}</ref>

The benefit of a low resting metabolism is that it requires far less fuel to sustain bodily functions. By using temperature variations in their surroundings, or by remaining cold when they do not need to move, reptiles can save considerable amounts of energy compared to endothermic animals of the same size.<ref>Campbell, N.A. & Reece, J.B. (2006): Outlines & Highlights for Essential Biology. ''Academic Internet Publishers''. 396 pp. {{ISBN|978-0-8053-7473-5}}</ref> A crocodile needs from a tenth to a fifth of the food necessary for a [[lion]] of the same weight and can live half a year without eating.<ref name=Garnett>{{cite journal|last=Garnett|first=S. T.|year= 2009|title=Metabolism and survival of fasting Estuarine crocodiles|journal=Journal of Zoology|number=208|volume=4|pages=493–502|doi=10.1111/j.1469-7998.1986.tb01518.x}}</ref> Lower food requirements and adaptive metabolisms allow reptiles to dominate the animal life in regions where net [[calorie]] availability is too low to sustain large-bodied mammals and birds.

It is generally assumed that reptiles are unable to produce the sustained high energy output necessary for long distance chases or flying.<ref>{{cite book |author1=Willmer, P. |author2=Stone, G. |author3=Johnston, I.A. |year=2000 |title=Environmental Physiology of Animals |publisher=Blackwell Science |place=London, UK  |isbn=978-0-632-03517-5}}</ref> Higher energetic capacity might have been responsible for the evolution of [[warm-blooded]]ness in birds and mammals.<ref>{{cite journal | last1 = Bennett | first1 = A. | last2 = Ruben | first2 = J. | year = 1979 | title = Endothermy and Activity in Vertebrates | journal = [[Science (journal)|Science]] | volume = 206 | issue = 4419 | pages = 649–654 | doi = 10.1126/science.493968 | pmid = 493968 | url = http://compphys.bio.uci.edu/bennett/pubs/30.pdf | bibcode = 1979Sci...206..649B | citeseerx = 10.1.1.551.4016 | access-date = 2017-10-27 | archive-date = 2017-08-11 | archive-url = https://web.archive.org/web/20170811152427/http://compphys.bio.uci.edu/bennett/pubs/30.pdf | url-status = dead }}</ref> However, investigation of correlations between active capacity and [[Thermoregulation|thermophysiology]] show a weak relationship.<ref name="CGF1">{{cite journal | author = Farmer, C.G. | year = 2000 | title = Parental care: The key to understanding endothermy and other convergent features in birds and mammals | journal = American Naturalist | volume = 155 | issue = 3 | pages = 326–334 | pmid = 10718729 | s2cid = 17932602 | doi = 10.1086/303323 | bibcode = 2000ANat..155..326F }}</ref> Most extant reptiles are carnivores with a sit-and-wait feeding strategy; whether reptiles are cold blooded due to their ecology <!-- 'or because their metabolism is a result of their ecology' : As this it is just a restatement of 'reptiles are cold blooded due to their ecology', essentially it was saying whether A was because of B or A was because of B, which is stupid! --> is not clear. Energetic studies on some reptiles have shown active capacities equal to or greater than similar sized warm-blooded animals.<ref>{{cite journal | last1 = Hicks | first1 = J.W.  | last2 = Farmer | first2 = C.G. | year = 1999 | title = Gas exchange potential in reptilian lungs: Implications for the dinosaur-avian connection | journal = Respiratory Physiology | volume = 117 | issue = 2–3 | pages = 73–83 | pmid=10563436 | doi = 10.1016/S0034-5687(99)00060-2}}</ref>