Editing Tyrannosaurus (section)

===Thermoregulation===
{{Main|Physiology of dinosaurs}}
[[File:Tyrannosaurus rex mmartyniuk.png|thumb|left|Restoration showing partial feathering]]
''Tyrannosaurus'', like most dinosaurs, was long thought to have an [[ectotherm]]ic ("cold-blooded") reptilian [[metabolism]]. The idea of dinosaur ectothermy was challenged by scientists like [[Robert T. Bakker]] and [[John Ostrom]] in the early years of the "[[Dinosaur Renaissance]]", beginning in the late 1960s.<ref name="bakker1968">{{Cite journal |last=Bakker |first=R. T. |author-link=Robert T. Bakker |year=1968 |title=The superiority of dinosaurs |url=http://bio.fsu.edu/~amarquez/Evolutionary%20Morphology%20fall%202004/Bakker/Bakker%201968%20-%20Superiority%20of%20DInos.pdf  |journal=Discovery |volume=3 |issue=2 |pages=11–12 |archive-url=https://web.archive.org/web/20060909131058/http://bio.fsu.edu/~amarquez/Evolutionary%20Morphology%20fall%202004/Bakker/Bakker%201968%20-%20Superiority%20of%20DInos.pdf |archive-date=September 9, 2006 |access-date=October 7, 2008}}</ref><ref name="bakker1972">{{Cite journal |last=Bakker |first=R. T. |s2cid=4176132 |author-link=Robert T. Bakker |year=1972 |title=Anatomical and ecological evidence of endothermy in dinosaurs |url=http://bio.fsu.edu/~amarquez/Evolutionary%20Morphology%20fall%202004/Bakker/14-%20Bakker%201972%20-%20dino%20endothermy.pdf  |journal=Nature |volume=238 |issue=5359 |pages=81–85 |bibcode=1972Natur.238...81B |doi=10.1038/238081a0 |archive-url=https://web.archive.org/web/20060909173036/http://bio.fsu.edu/~amarquez/Evolutionary%20Morphology%20fall%202004/Bakker/14-%20Bakker%201972%20-%20dino%20endothermy.pdf |archive-date=September 9, 2006 |access-date=October 7, 2008}}</ref> ''T. rex'' itself was claimed to have been [[Warm-blooded|endothermic]] ("warm-blooded"), implying a very active lifestyle.<ref name="bakker1986" /> Since then, several paleontologists have sought to determine the ability of ''Tyrannosaurus'' to [[thermoregulation|regulate]] its body temperature. Histological evidence of high growth rates in young ''T. rex'', comparable to those of mammals and birds, may support the hypothesis of a high metabolism. Growth curves indicate that, as in mammals and birds, ''T. rex'' growth was limited mostly to immature animals, rather than the [[indeterminate growth]] seen in most other [[vertebrate]]s.<ref name="hornerpadian2004" />

[[Isotopes of oxygen|Oxygen isotope]] ratios in fossilized bone are sometimes used to determine the temperature at which the bone was deposited, as the ratio between certain isotopes correlates with temperature. In one specimen, the isotope ratios in bones from different parts of the body indicated a temperature difference of no more than {{convert|4|to|5|C-change|0}} between the vertebrae of the torso and the [[tibia]] of the lower leg. This small temperature range between the body core and the extremities was claimed by paleontologist Reese Barrick and [[geochemistry|geochemist]] William Showers to indicate that ''T. rex'' maintained a constant internal body temperature ([[homeotherm]]y) and that it enjoyed a metabolism somewhere between ectothermic reptiles and endothermic mammals.<ref name="barrettshowers1994">{{Cite journal |last1=Barrick |first1=R. E. |last2=Showers |first2=W. J. |s2cid=39392327 |date=1994 |title=Thermophysiology of ''Tyrannosaurus rex'': Evidence from Oxygen Isotopes |journal=[[Science (journal)|Science]] |volume=265 |issue=5169 |pages=222–224 |bibcode=1994Sci...265..222B |doi=10.1126/science.265.5169.222 |pmid=17750663 }}</ref> Other scientists have pointed out that the ratio of oxygen isotopes in the fossils today does not necessarily represent the same ratio in the distant past, and may have been altered during or after fossilization ([[diagenesis]]).<ref name="truemanetal2003">{{Cite journal |last1=Trueman |first1=C. |last2=Chenery |first2=C. |last3=Eberth |first3=D. A. |last4=Spiro |first4=B. |s2cid=130658189 |year=2003 |title=Diagenetic effects on the oxygen isotope composition of bones of dinosaurs and other vertebrates recovered from terrestrial and marine sediments |journal=Journal of the Geological Society |volume=160 |issue=6 |pages=895–901 |doi=10.1144/0016-764903-019 |bibcode=2003JGSoc.160..895T |url=http://doc.rero.ch/record/14987/files/PAL_E2137.pdf |archive-date=April 4, 2023 |access-date=February 2, 2023 |archive-url=https://web.archive.org/web/20230404175035/https://doc.rero.ch/record/14987/files/PAL_E2137.pdf |url-status=live }}</ref> Barrick and Showers have defended their conclusions in subsequent papers, finding similar results in another theropod dinosaur from a different continent and tens of millions of years earlier in time (''[[Giganotosaurus]]'').<ref name="barrickshowers1999">{{Cite journal |last1=Barrick |first1=R. E. |last2=Showers |first2=W. J. |date=1999 |title=Thermophysiology and biology of ''Giganotosaurus'': comparison with ''Tyrannosaurus'' |url=http://palaeo-electronica.org/1999_2/gigan/issue2_99.htm |journal=Palaeontologia Electronica |volume=2 |issue=2 |access-date=October 7, 2008 |archive-date=May 17, 2011 |archive-url=https://web.archive.org/web/20110517220816/http://palaeo-electronica.org/1999_2/gigan/issue2_99.htm  }}</ref> [[Ornithischia]]n dinosaurs also showed evidence of homeothermy, while [[varanidae|varanid]] [[lizard]]s from the same formation did not.<ref name="barrickstevens1997">{{Cite book |title=The Complete Dinosaur |last1=Barrick |first1=R. E. |last2=Stoskopf |first2=M. K. |last3=Showers |first3=W. J. |publisher=Indiana University Press |year=1999 |isbn=978-0-253-21313-6 |editor-last=Farlow |editor-first=J. O. |location=Bloomington |pages=474–490 |chapter=Oxygen isotopes in dinosaur bones |editor-last2=Brett-Surman |editor-first2=M. K.}}</ref> In 2022, Wiemann and colleagues used a different approach—the [[spectroscopy]] of lipoxidation signals, which are byproducts of [[oxidative phosphorylation]] and correlate with metabolic rates—to show that various dinosaur genera including ''Tyrannosaurus'' had endothermic metabolisms, on par with that of modern birds and higher than that of mammals. They also suggested that such a metabolism was ancestrally common to all dinosaurs.<ref name="wiemann2022">{{cite journal |last1=Wiemann |first1=J. |last2=Menéndez |first2=I. |last3=Crawford |first3=J.M. |first4=M. |last4=Fabbri |first5=J.A. |last5=Gauthier |first6=P.M. |last6=Hull |first7=M.A. |last7=Norell |first8=D.E.G. |last8=Briggs |title=Fossil biomolecules reveal an avian metabolism in the ancestral dinosaur |journal=Nature |year=2022 |volume=606 |issue=7914 |pages=522–526 |doi=10.1038/s41586-022-04770-6|pmid=35614213 |bibcode=2022Natur.606..522W |s2cid=249064466 |url=https://resolver.caltech.edu/CaltechAUTHORS:20220531-924660000 }}</ref>

Even if ''T. rex'' does exhibit evidence of homeothermy, it does not necessarily mean that it was endothermic. Such thermoregulation may also be explained by [[gigantothermy]], as in some living [[sea turtle]]s.<ref name="paladinoetal1997">{{Cite book |title=The Complete Dinosaur |last1=Paladino |first1=F. V. |last2=Spotila |first2=J. R. |last3=Dodson |first3=P. |publisher=Indiana University Press |year=1999 |isbn=978-0-253-21313-6 |editor-last=Farlow |editor-first=J. O. |location=Bloomington |pages=491–504 |chapter=A blueprint for giants: modeling the physiology of large dinosaurs |editor-last2=Brett-Surman |editor-first2=M. K.}}</ref><ref name="chinsamyhillenius2004">{{Cite book |title=The dinosauria |url=https://archive.org/details/dinosauriandedit00weis |url-access=limited |last1=Chinsamy |first1=A. |last2=Hillenius |first2=W. J. |publisher=University of California Press |year=2004 |isbn=978-0-520-24209-8 |editor-last=Weishampel |editor-first=D. B. |location=Berkeley |pages=[https://archive.org/details/dinosauriandedit00weis/page/n661 643]–659 |chapter=Physiology of nonavian dinosaurs |editor-last2=Dodson |editor-first2=P. |editor-last3=Osmólska |editor-first3=H.}}</ref><ref>{{Cite journal |last=Seymour |first=R. S. |date=July 5, 2013 |title=Maximal Aerobic and Anaerobic Power Generation in Large Crocodiles versus Mammals: Implications for Dinosaur Gigantothermy |journal=PLOS ONE |volume=8 |issue=7 |pages=e69361 |bibcode=2013PLoSO...869361S |doi=10.1371/journal.pone.0069361 |issn=1932-6203 |pmc=3702618 |pmid=23861968|doi-access=free }}</ref> Similar to contemporary crocodilians, openings (dorsotemporal fenestrae) in the skull roofs of ''Tyrannosaurus'' may have aided thermoregulation.<ref name="holliday2019">{{cite journal |last1=Holliday |first1=C.M. |last2=Porter |first2=W.R. |last3=Vilet |first3=K.A. |last4=Witmer |first4=L.M. |year=2019 |title=The Frontoparietal Fossa and Dorsotemporal Fenestra of Archosaurs and Their Significance for Interpretations of Vascular and Muscular Anatomy in Dinosaurs |journal=The Anatomical Record |volume=303 |issue=4 |pages=1060–1074 |doi=10.1002/ar.24218|pmid=31260177 |s2cid=195756776 |doi-access=free }}</ref>