Editing Tyrannosaurus (section)

==Paleobiology==

===Life history===
[[File:Baby T-rex 0496.JPG|thumb|Illustration of a juvenile ''Tyrannosaurus rex'']]
The identification of several specimens as juvenile ''T. rex'' has allowed scientists to document [[ontogeny|ontogenetic]] changes in the species, estimate the lifespan, and determine how quickly the animals would have grown. The smallest known individual ([[Los Angeles County Museum of Natural History|LACM]] 28471, the "Jordan theropod") is estimated to have weighed only {{cvt|30|kg}}, while the largest adults, such as [[Field Museum of Natural History|FMNH]] PR2081 (Sue) most likely weighed about {{cvt|5650|kg}}. [[Histology|Histologic]] analysis of ''T. rex'' bones showed LACM 28471 had aged only 2 years when it died, while Sue was 28 years old, an age which may have been close to the maximum for the species.<ref name="ericksonetal2004" />

[[File:Tyrannosauridae growth rates.svg|thumb|left|A graph showing the hypothesized growth curve, body mass versus age (drawn in black, with other tyrannosaurids for comparison). Based on Erickson and colleagues 2004]]
Histology has also allowed the age of other specimens to be determined. Growth curves can be developed when the ages of different specimens are plotted on a graph along with their mass. A ''T. rex'' growth curve is S-shaped, with juveniles remaining under {{cvt|1800|kg}} until approximately 14 years of age, when body size began to increase dramatically. During this rapid growth phase, a young ''T. rex'' would gain an average of {{cvt|600|kg}} a year for the next four years. At 18 years of age, the curve plateaus again, indicating that growth slowed dramatically. For example, only {{cvt|600|kg}} separated the 28-year-old Sue from a 22-year-old Canadian specimen ([[Royal Tyrrell Museum of Palaeontology|RTMP]] 81.12.1).<ref name="ericksonetal2004" /> A 2004 histological study performed by different workers corroborates these results, finding that rapid growth began to slow at around 16 years of age.<ref name="hornerpadian2004">{{Cite journal |last1=Horner |first1=J. R. |last2=Padian |first2=K. |date=2004 |title=Age and growth dynamics of Tyrannosaurus rex |journal=Proceedings: Biological Sciences |volume=271 |issue=1551 |pages=1875–80 |doi=10.1098/rspb.2004.2829 |pmc=1691809 |pmid=15347508}}</ref>

A study by Hutchinson and colleagues in 2011 corroborated the previous estimation methods in general, but their estimation of peak growth rates is significantly higher; it found that the "maximum growth rates for T. rex during the exponential stage are 1790 kg/year".<ref name="Hutchinsonet.al.2011" /> Although these results were much higher than previous estimations, the authors noted that these results significantly lowered the great difference between its actual growth rate and the one which would be expected of an animal of its size.<ref name="Hutchinsonet.al.2011" /> The sudden change in growth rate at the end of the growth spurt may indicate physical maturity, a hypothesis which is supported by the discovery of medullary tissue in the [[femur]] of a 16 to 20-year-old ''T. rex'' from Montana ([[Museum of the Rockies|MOR]] 1125, also known as [[B-rex]]). Medullary tissue is found only in female birds during ovulation, indicating that B-rex was of reproductive age.<ref name="schweitzeretal2005">{{Cite journal |last1=Schweitzer |first1=M. H. |last2=Wittmeyer |first2=J. L. |last3=Horner |first3=J. R. |s2cid=30264554 |date=2005 |title=Gender-specific reproductive tissue in ratites and ''Tyrannosaurus rex'' |journal=Science |volume=308 |issue=5727 |pages=1456–60 |bibcode=2005Sci...308.1456S |doi=10.1126/science.1112158 |pmid=15933198 |url=http://doc.rero.ch/record/14767/files/PAL_E1895.pdf |archive-date=March 12, 2023 |access-date=November 23, 2022 |archive-url=https://web.archive.org/web/20230312052627/https://doc.rero.ch/record/14767/files/PAL_E1895.pdf |url-status=live }}</ref> Further study indicates an age of 18 for this specimen.<ref name="LW08">{{Cite journal |last1=Lee |first1=A. H. |last2=Werning |first2=S. |year=2008 |title=Sexual maturity in growing dinosaurs does not fit reptilian growth models |journal=Proceedings of the National Academy of Sciences |volume=105 |issue=2 |pages=582–587 |bibcode=2008PNAS..105..582L |doi=10.1073/pnas.0708903105 |pmc=2206579 |pmid=18195356|doi-access=free }}</ref> In 2016, it was finally confirmed by Mary Higby Schweitzer and Lindsay Zanno and colleagues that the soft tissue within the femur of MOR 1125 was medullary tissue. This also confirmed the identity of the specimen as a female. The discovery of medullary bone tissue within ''Tyrannosaurus'' may prove valuable in determining the sex of other dinosaur species in future examinations, as the chemical makeup of medullary tissue is unmistakable.<ref>{{Cite journal |last1=Schweitzer |first1=M. H. |last2=Zheng |first2=W. |last3=Zanno |first3=L. |last4=Werning |first4=S. |last5=Sugiyama |first5=T. |date=2016 |title=Chemistry supports the identification of gender-specific reproductive tissue in Tyrannosaurus rex |journal=Scientific Reports |volume=6 |issue=23099 |page=23099 |doi=10.1038/srep23099 |pmc=4791554 |pmid=26975806|bibcode=2016NatSR...623099S }}</ref> Other tyrannosaurids exhibit extremely similar growth curves, although with lower growth rates corresponding to their lower adult sizes.<ref name="ericksonetal2006">{{Cite journal |last1=Erickson |first1=G. M. |last2=Currie |first2=P. J. |last3=Inouye |first3=B. D. |last4=Winn |first4=A. A. |s2cid=34191607 |date=2006 |title=Tyrannosaur life tables: an example of nonavian dinosaur population biology |journal=Science |volume=313 |issue=5784 |pages=213–7 |bibcode=2006Sci...313..213E |doi=10.1126/science.1125721 |pmid=16840697}}</ref>

[[File:Ontogram of Tyrannosaurus rex.png|thumb|Diagram showing growth stages]]
An additional study published in 2020 by Woodward and colleagues, for the journal ''Science Advances'' indicates that during their growth from juvenile to adult, ''Tyrannosaurus'' was capable of slowing down its growth to counter environmental factors such as lack of food. The study, focusing on two juvenile specimens between 13 and 15 years old housed at the Burpee Museum in Illinois, indicates that the rate of maturation for ''Tyrannosaurus'' was dependent on resource abundance. This study also indicates that in such changing environments, ''Tyrannosaurus'' was particularly well-suited to an environment that shifted yearly in regards to resource abundance, hinting that other midsize predators might have had difficulty surviving in such harsh conditions and explaining the niche partitioning between juvenile and adult tyrannosaurs. The study further indicates that ''Tyrannosaurus'' and the dubious genus ''Nanotyrannus'' are synonymous, due to analysis of the growth rings in the bones of the two specimens studied.<ref>{{cite journal|last1=Woodward |first1=Holly N |last2=Tremaine |first2=Katie |last3=Williams |first3=Scott A |last4=Zanno |first4=Lindsay E |last5=Horner |first5=John R |last6=Myhrvold |first6=Nathan |date=January 1, 2020 |title=Growing up Tyrannosaurus rex: Osteohistology refutes the pygmy "Nanotyrannus" and supports ontogenetic niche partitioning in juvenile Tyrannosaurus |volume=6 |issue=1 |pages=eaax6250 |journal=Science Advances |pmid=31911944 |doi=10.1126/sciadv.aax6250 |pmc=6938697 |bibcode=2020SciA....6.6250W }}</ref><ref>{{cite web|url=https://www.nationalgeographic.com/science/2020/01/nanotyrannus-fossils-really-are-teenage-t-rex-dinosaur-growth-rates/ |archive-url=https://web.archive.org/web/20200101225622/https://www.nationalgeographic.com/science/2020/01/nanotyrannus-fossils-really-are-teenage-t-rex-dinosaur-growth-rates/ |url-status=dead |archive-date=January 1, 2020 |last=Greshko |first=Michael |date=January 1, 2020 |title=These sleek predatory dinosaurs really are teenage T. rex |work=[[National Geographic]] |access-date=January 2, 2020}}</ref>

Over half of the known ''T. rex'' specimens appear to have died within six years of reaching sexual maturity, a pattern which is also seen in other tyrannosaurs and in some large, long-lived birds and mammals today. These species are characterized by high infant mortality rates, followed by relatively low mortality among juveniles. Mortality increases again following sexual maturity, partly due to the stresses of reproduction. One study suggests that the rarity of juvenile ''T. rex'' fossils is due in part to low juvenile mortality rates; the animals were not dying in large numbers at these ages, and thus were not often fossilized. This rarity may also be due to the incompleteness of the [[fossil record]] or to the bias of fossil collectors towards larger, more spectacular specimens.<ref name="ericksonetal2006" /> In a 2013 lecture, Thomas Holtz Jr. suggested that dinosaurs "lived fast and died young" because they reproduced quickly whereas mammals have long lifespans because they take longer to reproduce.<ref name="HoltzLecture2013">{{Cite AV media |url=https://www.youtube.com/watch?v=sqkqkxYGNZc  |archive-url=https://ghostarchive.org/varchive/youtube/20211211/sqkqkxYGNZc| archive-date=December 11, 2021 |url-status=live|title=The Life and Times of Tyrannosaurus rex, with Dr. Thomas Holtz |date=March 19, 2013 |last=Holtz |first=T. R. Jr. |publisher=[[Burke Museum of Natural History and Culture]] |location=Seattle, WA |access-date=October 12, 2013 |orig-date=Lecture held March 8, 2013 |medium=Lecture}}{{cbignore}}</ref> Gregory S. Paul also writes that ''Tyrannosaurus'' reproduced quickly and died young but attributes their short lifespans to the dangerous lives they lived.<ref name="Paul2008Highrisklife">{{Cite book |title=''Tyrannosaurus'', The Tyrant King |last=Paul |first=G. S. |publisher=Indiana University Press |year=2008 |isbn=978-0-253-35087-9 |editor-last=Larson |editor-first=P. L. |pages=307–345 |chapter=Chapter 18: The Extreme Life Style and Habits of the Gigantic Tyrannosaurid Superpredators of the Cretaceous North America and Asia |access-date=September 14, 2013 |editor-last2=Carpenter |editor-first2=K. |chapter-url=https://books.google.com/books?id=5WH9RnfKco4C&pg=PA307}}</ref>

===Skin and possible filamentous feathering===
{{Main|Feathered dinosaur}}
[[File:Wyrex Tyrannosaurus Skin Impression.jpg|thumb|Fossilized skin impressions from the tail region of a ''Tyrannosaurus rex'', [[Houston Museum of Natural Science]]]]
The discovery of [[feathered dinosaur]]s led to debate regarding whether, and to what extent, ''Tyrannosaurus'' might have been feathered.<ref name="Belletal2017" /><ref name="NYT-20190307">{{Cite news |url=https://www.nytimes.com/2019/03/07/arts/design/t-rex-exhibition-american-museum-of-natural-history.html |archive-url=https://web.archive.org/web/20190308002505/https://www.nytimes.com/2019/03/07/arts/design/t-rex-exhibition-american-museum-of-natural-history.html |archive-date=March 8, 2019 |url-access=subscription |url-status=live |title=T. Rex Like You Haven't Seen Him: With Feathers |last=Farago |first=J. |date=March 7, 2019 |work=[[The New York Times]] |access-date=March 7, 2019}}</ref> Filamentous structures, which are commonly recognized as the precursors of [[feather]]s, have been reported in the small-bodied, basal tyrannosauroid ''[[Dilong paradoxus]]'' from the Early Cretaceous [[Yixian Formation]] of China in 2004.<ref name="xuetal2004">{{Cite journal |last1=Xing |first1=X. |last2=Norell |first2=M. A. |last3=Kuang |first3=X. |last4=Wang |first4=X. |last5=Zhao |first5=Q. |last6=Jia |first6=C. |s2cid=4381777 |date=October 7, 2004 |title=Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids |journal=[[Nature (journal)|Nature]] |volume=431 |issue=7009 |pages=680–684 |bibcode=2004Natur.431..680X |doi=10.1038/nature02855 |pmid=15470426|url=http://doc.rero.ch/record/15283/files/PAL_E2582.pdf }}</ref> Because [[integument]]ary impressions of larger tyrannosauroids known at that time showed evidence of [[scale (anatomy)|scales]], the researchers who studied ''Dilong'' speculated that insulating feathers might have been lost by larger species due to their smaller surface-to-volume ratio.<ref name="xuetal2004" /> The subsequent discovery of the giant species ''[[Yutyrannus huali]]'', also from the Yixian, showed that even some large tyrannosauroids had feathers covering much of their bodies, casting doubt on the hypothesis that they were a size-related feature.<ref name="yutyrannus">{{Cite journal |last1=Xing |first1=X. |last2=Wang |first2=K. |last3=Zhang |last4=Ma |first4=Q. |last5=Xing |first5=L. |last6=Sullivan |first6=C. |last7=Hu |first7=D. |last8=Cheng |first8=S. |last9=Wang |first9=S. |s2cid=29689629 |date=April 5, 2012 |title=A gigantic feathered dinosaur from the Lower Cretaceous of China |url=http://www.xinglida.net/pdf/Xu_et_al_2012_Yutyrannus.pdf  |journal=Nature |volume=484 |issue=7392 |pages=92–95 |bibcode=2012Natur.484...92X |doi=10.1038/nature10906 |pmid=22481363 |archive-url=https://web.archive.org/web/20120417134949/http://www.xinglida.net/pdf/Xu_et_al_2012_Yutyrannus.pdf |archive-date=April 17, 2012}}</ref> A 2017 study reviewed known skin impressions of tyrannosaurids, including those of a ''Tyrannosaurus'' specimen nicknamed "Wyrex" (HMNS 2006.1743.01, formerly known as BHI 6230) which preserves patches of mosaic scales on the tail, hip, and neck.<ref name="Belletal2017"/> The study concluded that feather covering of large tyrannosaurids such as ''Tyrannosaurus'' was, if present, limited to the upper side of the trunk.<ref name="Belletal2017">{{Cite journal |last1=Bell |first1=P. R. |last2=Campione |first2=N. E. |last3=Persons IV |first3=W. S. |last4=Currie |first4=P. J. |last5=Larson |first5=P. L. |last6=Tanke |first6=D. H. |last7=Bakker |first7=R. T. |date=2017 |title=Tyrannosauroid integument reveals conflicting patterns of gigantism and feather evolution |journal=Biology Letters |volume=13 |issue=6 |page=20170092 |doi=10.1098/rsbl.2017.0092|pmid=28592520 |pmc=5493735 }}</ref>

A conference abstract published in 2016 posited that theropods such as ''Tyrannosaurus'' had their upper teeth covered in lips, instead of bare teeth as seen in [[crocodilia]]ns. This was based on the presence of [[Tooth enamel|enamel]], which according to the study needs to remain hydrated, an issue not faced by aquatic animals like crocodilians.<ref name=":0">{{Cite journal |last1=Reisz |first1=R. R. |last2=Larson |first2=D. |year=2016 |title=Dental anatomy and skull length to tooth size ratios support the hypothesis that theropod dinosaurs had lips |url=https://ejournals.library.ualberta.ca/index.php/VAMP/article/download/28196/20702 |journal=4th Annual Meeting, 2016, Canadian Society of Vertebrate Palaeontology |issn=2292-1389 |archive-date=April 4, 2017 |access-date=April 3, 2017 |archive-url=https://web.archive.org/web/20170404043155/https://ejournals.library.ualberta.ca/index.php/VAMP/article/download/28196/20702 |url-status=live }}</ref> However, there has been criticism where it favors the idea for lips, with the 2017 analytical study proposing that tyrannosaurids had large, flat scales on their snouts instead of lips, as modern crocodiles do.<ref name="carr2017">{{Cite journal |last1=Carr |first1=T. D. |last2=Varricchio |first2=D. J. |last3=Sedlmayr |first3=J. C. |last4=Roberts |first4=E. M. |last5=Moore |first5=J. R. |date=March 30, 2017 |title=A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system |journal=Scientific Reports |language=en |volume=7 |page=44942 |bibcode=2017NatSR...744942C |doi=10.1038/srep44942 |issn=2045-2322 |pmc=5372470 |pmid=28358353}}</ref><ref name="naish2018">{{Cite web |url=https://blogs.scientificamerican.com/tetrapod-zoology/the-sensitive-face-of-a-big-predatory-dinosaur/ |title=The Sensitive Face of a Big Predatory Dinosaur |last=Naish |first=D. |website=Tetrapod Zoology |publisher=Scientific American Blog Network |access-date=December 5, 2018 |archive-date=December 6, 2018 |archive-url=https://web.archive.org/web/20181206102230/https://blogs.scientificamerican.com/tetrapod-zoology/the-sensitive-face-of-a-big-predatory-dinosaur/ |url-status=live }}</ref> But crocodiles possess rather cracked keratinized skin, not flat scales; by observing the hummocky rugosity of tyrannosaurids, and comparing it to extant lizards, researchers have found that tyrannosaurids had squamose scales rather than a crocodillian-like skin.<ref>{{cite web |title=MORPHOLOGY, TAXONOMY, AND PHYLOGENETIC RELATIONSHIPS OF THE MONTEVIALE CROCODYLIANS (OLIGOCENE, ITALY). p. 67 |url=https://scholar.google.com/scholar?hl=en&as_sdt=0%2C14&q=MORPHOLOGY%2C+TAXONOMY%2C+AND+PHYLOGENETIC+RELATIONSHIPS+OF+THE+MONTEVIALE+CROCODYLIANS+%28OLIGOCENE%2C+ITALY%29.&btnG= |website=The Annual Symposium of Vertebrate Palaeontology and Comparative Anatomy |access-date=October 9, 2020 |archive-date=November 10, 2021 |archive-url=https://web.archive.org/web/20211110091020/https://scholar.google.com/scholar?hl=en&as_sdt=0%2C14&q=MORPHOLOGY%2C+TAXONOMY%2C+AND+PHYLOGENETIC+RELATIONSHIPS+OF+THE+MONTEVIALE+CROCODYLIANS+%28OLIGOCENE%2C+ITALY%29.&btnG= |url-status=live }}</ref><ref>{{cite journal |last1=Milinkovitch |first1=Michel |last2=Manukyan |first2=Liana |last3=Debry |first3=Adrien |last4=Di-Poi |first4=Nicolas |last5=Martin |first5=Samuel |last6=Singh |first6=Daljit |last7=Lambert |first7=Dominique |last8=Zwicker |first8=Matthias |title=Crocodile Head Scales Are Not Developmental Units But Emerge from Physical Cracking |journal=Science |date=January 4, 2013 |volume=339 |issue=6115 |pages=78–81 |doi=10.1126/science.1226265 |pmid=23196908 |bibcode=2013Sci...339...78M |s2cid=6859452 |doi-access=free }}</ref>

In 2023, Cullen and colleagues supported the idea that theropods like tyrannosaurids had lips based on anatomical patterns, such as those of the foramina on their face and jaws, more similar to those of modern [[squamate]]s such as [[monitor lizard]]s or [[marine iguana]]s than those of modern [[crocodilia]]ns like [[alligator]]s. Comparison of the teeth of ''Daspletosaurus'' and [[American alligator]]s shows that the enamel of tyrannosaurids had no significant wear and that the teeth of modern crocodilians were eroded on the labial side and were substantially worn. This suggests that it is likely that theropod teeth were kept wet by lips. On the basis of the relationship between hydration and wear resistance, the authors argued that it is unlikely that the teeth of theropods, including tyrannosaurids, would have remained unworn when exposed for a long time, because it would have been hard to maintain hydration. The authors also performed regression analyses to demonstrate the relationship between tooth height and skull length, and found that [[varanid]]s like the [[crocodile monitor]] had substantially greater ratios of tooth height to skull length than those of ''Tyrannosaurus'', indicating that the teeth of theropods were not too big to be covered by extraoral tissues when the mouth was closed.<ref name=CullenEtAl23/>

===Sexual dimorphism===
[[File:MUJA 04.jpg|thumb|upright|left|Skeleton casts mounted in a mating position, [[Jurassic Museum of Asturias]]]]
As the number of known specimens increased, scientists began to analyze the variation between individuals and discovered what appeared to be two distinct body types, or ''morphs'', similar to some other theropod species. As one of these morphs was more solidly built, it was termed the 'robust' morph while the other was termed '[[Wikt:gracile|gracile]]'. Several [[morphology (biology)|morphological]] differences associated with the two morphs were used to analyze [[sexual dimorphism]] in ''T. rex'', with the 'robust' morph usually suggested to be female. For example, the [[pelvis]] of several 'robust' specimens seemed to be wider, perhaps to allow the passage of [[Egg (biology)|eggs]].<ref name="carpenter1990">{{Cite book |title=Dinosaur Systematics: Approaches and Perspectives |last=Carpenter |first=K. |publisher=[[Cambridge University Press]] |year=1992 |isbn=978-0-521-43810-0 |editor-last=Carpenter |editor-first=K. |location=[[Cambridge]] |pages=141–145 |chapter=Variation in ''Tyrannosaurus rex'' |author-link=Kenneth Carpenter |editor-last2=Currie |editor-first2=P. J.}}</ref> It was also thought that the 'robust' morphology correlated with a reduced [[chevron (anatomy)|chevron]] on the first tail vertebra, also ostensibly to allow eggs to pass out of the [[reproductive system|reproductive tract]], as had been erroneously reported for [[crocodile]]s.<ref name="larson1994">{{Cite book |last=Larson |first=P. L. |year=1994 |editor-last=Rosenberg |editor-first=G. D. |editor2-last=Wolberg |editor2-first=D. L. |title=Dino Fest |publisher=The Paleontological Society Special Publications |chapter=''Tyrannosaurus'' sex |volume=7 |pages=139–155}}</ref>

In recent years, evidence for sexual dimorphism has been weakened. A 2005 study reported that previous claims of sexual dimorphism in crocodile chevron anatomy were in error, casting doubt on the existence of similar dimorphism between ''T. rex'' sexes.<ref name="ericksonetal2005">{{Cite journal |last1=Erickson |first1=G. M. |last2=Kristopher |first2=L. A. |last3=Larson |first3=P. |year=2005 |title=Androgynous rex&nbsp;– the utility of chevrons for determining the sex of crocodilians and non-avian dinosaurs |journal=Zoology (Jena, Germany) |volume=108 |issue=4 |pages=277–86 |doi=10.1016/j.zool.2005.08.001 |pmid=16351976 |bibcode=2005Zool..108..277E |url=http://doc.rero.ch/record/14378/files/PAL_E1827.pdf |archive-date=April 4, 2023 |access-date=February 2, 2023 |archive-url=https://web.archive.org/web/20230404163719/https://doc.rero.ch/record/14378/files/PAL_E1827.pdf |url-status=live }}</ref> A full-sized chevron was discovered on the first tail vertebra of Sue, an extremely robust individual, indicating that this feature could not be used to differentiate the two morphs anyway. As ''T. rex'' specimens have been found from [[Saskatchewan]] to [[New Mexico]], differences between individuals may be indicative of geographic variation rather than sexual dimorphism. The differences could also be age-related, with 'robust' individuals being older animals.<ref name="brochu2003" />

Only a single ''Tyrannosaurus'' specimen has been conclusively shown to belong to a specific sex. Examination of B-rex demonstrated the preservation of [[soft tissue]] within several bones. Some of this tissue has been identified as a medullary tissue, a specialized tissue grown only in modern birds as a source of [[calcium]] for the production of [[eggshell]] during [[ovulation]]. As only female birds lay eggs, medullary tissue is only found naturally in females, although males are capable of producing it when injected with female reproductive [[hormone]]s like [[estrogen]]. This strongly suggests that B-rex was female and that she died during ovulation.<ref name="schweitzeretal2005" /> Recent research has shown that medullary tissue is never found in crocodiles, which are thought to be the closest living relatives of dinosaurs. The shared presence of medullary tissue in birds and other theropod dinosaurs is further evidence of the close [[evolution]]ary relationship between the two.<ref name="schweitzeretal2007">{{Cite journal |last1=Schweitzer |first1=M. H. |last2=Elsey |first2=R. M. |last3=Dacke |first3=C. G. |last4=Horner |first4=J. R. |last5=Lamm |first5=E. T. |date=2007 |title=Do egg-laying crocodilian (''Alligator mississippiensis'') archosaurs form medullary bone? |journal=Bone |volume=40 |issue=4 |pages=1152–8 |doi=10.1016/j.bone.2006.10.029 |pmid=17223615 }}</ref>

===Posture===
[[File:T. rex old posture.jpg|thumb|Outdated reconstruction (by [[Charles R. Knight]]), showing upright pose]]
Like many [[bipedal]] dinosaurs, ''T. rex'' was historically depicted as a 'living tripod', with the body at 45 degrees or less from the vertical and the tail dragging along the ground, similar to a [[kangaroo]]. This concept dates from [[Joseph Leidy]]'s 1865 reconstruction of ''[[Hadrosaurus]]'', the first to depict a dinosaur in a bipedal posture.<ref name="leidy1865">{{Cite journal |last=Leidy |first=J. |year=1865 |title=Memoir on the extinct reptiles of the Cretaceous formations of the United States |journal=Smithsonian Contributions to Knowledge |volume=14 |pages=1–135}}</ref> In 1915, convinced that the creature stood upright, [[Henry Fairfield Osborn]], former president of the American Museum of Natural History, further reinforced the notion in unveiling the first complete ''T. rex'' skeleton arranged this way. It stood in an upright pose for 77 years, until it was dismantled in 1992.<ref name="amnhsite">{{Cite web |url=http://www.amnh.org/exhibitions/expeditions/treasure_fossil/Treasures/Tyrannosaurus/tyrannos.html?dinos |title=''Tyrannosaurus'' |publisher=[[American Museum of Natural History]] |archive-url=https://web.archive.org/web/20081208143829/http://www.amnh.org/exhibitions/expeditions/treasure_fossil/Treasures/Tyrannosaurus/tyrannos.html?dinos |archive-date=December 8, 2008 |access-date=October 16, 2008}}</ref>

By 1970, scientists realized this pose was incorrect and could not have been maintained by a living animal, as it would have resulted in the [[Dislocation (medicine)|dislocation]] or weakening of several [[joint]]s, including the hips and the articulation between the head and the [[spinal column]].<ref name="newman1970">{{Cite journal |last=Newman |first=B. H. |year=1970 |title=Stance and gait in the flesh-eating ''Tyrannosaurus'' |journal=Biological Journal of the Linnean Society |volume=2 |issue=2 |pages=119–123 |doi=10.1111/j.1095-8312.1970.tb01707.x |url=https://zenodo.org/record/3674749 |archive-date=August 4, 2020 |access-date=March 15, 2020 |archive-url=https://web.archive.org/web/20200804080335/https://zenodo.org/record/3674749 |url-status=live }}</ref> The inaccurate AMNH mount inspired similar depictions in many films and paintings (such as [[Rudolph F. Zallinger|Rudolph Zallinger]]'s famous mural ''[[The Age of Reptiles]]'' in [[Yale University]]'s [[Peabody Museum of Natural History]])<ref>{{Cite web |url=http://peabody.yale.edu/exhibits/age-reptiles-mural |title=The Age of Reptiles Mural |year=2008 |publisher=Yale University |access-date=October 16, 2008 |archive-date=September 29, 2018 |archive-url=https://web.archive.org/web/20180929053007/http://peabody.yale.edu/exhibits/age-reptiles-mural  }}</ref> until the 1990s, when films such as ''[[Jurassic Park (film)|Jurassic Park]]'' introduced a more accurate posture to the general public.<ref>{{Cite journal |last1=Ross |first1=R. M. |last2=Duggan-Haas |first2=D. |last3=Allmon |first3=W. D. |s2cid=162343784 |year=2013 |title=The Posture of ''Tyrannosaurus rex'': Why Do Student Views Lag Behind the Science? |journal=Journal of Geoscience Education |volume=61 |issue=1 |pages=145–160 |bibcode=2013JGeEd..61..145R |doi=10.5408/11-259.1}}</ref> Modern representations in museums, art, and film show ''T. rex'' with its body approximately parallel to the ground with the tail extended behind the body to balance the head.<ref>{{Cite web |url=https://www.aaas.org/tyrannosaurus-rex-not-tripod-anymore |title=''Tyrannosaurus Rex'': Not a tripod anymore |website=American Association for the Advancement of Science |date=April 2, 2013 |access-date=December 5, 2018 |archive-date=December 6, 2018 |archive-url=https://web.archive.org/web/20181206053308/https://www.aaas.org/tyrannosaurus-rex-not-tripod-anymore |url-status=live }}</ref>

To sit down, ''Tyrannosaurus'' may have settled its weight backwards and rested its weight on a pubic boot, the wide expansion at the end of the pubis in some dinosaurs. With its weight rested on the pelvis, it may have been free to move the hindlimbs. Getting back up again might have involved some stabilization from the diminutive forelimbs.<ref>{{Cite web|last=Stevens|first=Kent A.|date=2011|title=Tyrannosaurus rex – "Rex, sit"|url=http://ix.cs.uoregon.edu/~kent/paleontology/Tyrannosaurus/index.html|access-date=July 26, 2020|website=ix.cs.uoregon.edu}}</ref><ref name="newman1970"/> The latter known as Newman's pushup theory has been debated. Nonetheless, ''Tyrannosaurus'' was probably able to get up if it fell, which only would have required placing the limbs below the center of gravity, with the tail as an effective counterbalance. Healed stress fractures in the forelimbs have been put forward both as evidence that the arms cannot have been very useful<ref>{{Cite web|title=If T. rex fell, how did it get up, given its tiny arms and low center of gravity?|url=https://www.scientificamerican.com/article/if-t-rex-fell-how-did-it/|access-date=July 26, 2020|website=Scientific American|language=en|archive-date=July 26, 2020|archive-url=https://web.archive.org/web/20200726053130/https://www.scientificamerican.com/article/if-t-rex-fell-how-did-it/|url-status=live}}</ref><ref name="Padian (2022)" /> and as evidence that they were indeed used and acquired wounds,<ref name="Stevens et.al.2008">Stevens K.A., Larson P, Willis E.D. & Anderson A. "Rex, sit: digital modeling of ''Tyrannosaurus rex'' at rest". In Larson P & Carpenter K (eds.). ''Tyrannosaurus rex, the tyrant king'' (Indiana University Press, 2008). p. 192-203</ref> like the rest of the body.

===Arms===
[[File:Tyrannosaurus resting pose.jpg|thumb|left|The forelimbs might have been used to help ''T.&nbsp;rex'' rise from a resting pose, as seen in this cast ([[Bucky (Tyrannosaurus rex)|Bucky]] specimen)]]
When ''T. rex'' was first discovered, the [[humerus]] was the only element of the forelimb known.<ref name="osborn1905">{{Cite journal |last=Osborn |first=H. F. |author-link=Henry Fairfield Osborn |year=1905 |title=''Tyrannosaurus'' and other Cretaceous carnivorous dinosaurs |journal=Bulletin of the AMNH |volume=21 |issue=14 |pages=259–265 |hdl=2246/1464|hdl-access=free }} Retrieved October 6, 2008.</ref> For the initial mounted skeleton as seen by the public in 1915, Osborn substituted longer, three-fingered forelimbs like those of ''[[Allosaurus]]''.<ref name="osborn1917" /> A year earlier, [[Lawrence Lambe]] described the short, two-fingered forelimbs of the closely related ''Gorgosaurus''.<ref name="lambe1914">{{Cite journal |last=Lambe |first=L. M. |author-link=Lawrence Lambe |year=1914 |title=On a new genus and species of carnivorous dinosaur from the Belly River Formation of Alberta, with a description of the skull of ''Stephanosaurus marginatus'' from the same horizon |journal=Ottawa Naturalist |volume=27 |pages=129–135}}</ref> This strongly suggested that ''T. rex'' had similar forelimbs, but this [[hypothesis]] was not confirmed until the first complete ''T. rex'' forelimbs were identified in 1989, belonging to MOR 555 (the "Wankel rex").<ref name="hornerlessem1993">{{Cite book |title=The complete T. rex |last1=Horner |first1=J. R. |last2=Lessem |first2=D. |publisher=[[Simon & Schuster]] |year=1993 |isbn=978-0-671-74185-3 |location=[[New York City]] |author-link=Jack Horner (paleontologist) |author-link2=Don Lessem |url=https://archive.org/details/completetrexhows00horn }}</ref><ref>{{Cite web|url=https://naturalhistory.si.edu/education/teaching-resources/paleontology/new-view-t-rex|title=A New View of T. Rex {{!}} Smithsonian National Museum of Natural History|date=April 13, 2020|archive-url=https://web.archive.org/web/20200413044033/https://naturalhistory.si.edu/education/teaching-resources/paleontology/new-view-t-rex|access-date=April 13, 2020|archive-date=April 13, 2020}}</ref> The remains of Sue also include complete forelimbs.<ref name="brochu2003" /> ''T. rex'' arms are very small relative to overall body size, measuring only {{convert|1|m|ft|sp=us}} long, and some scholars have labelled them as [[vestigial organs|vestigial]]. However, the bones show large areas for [[muscle]] attachment, indicating considerable strength. This was recognized as early as 1906 by Osborn, who speculated that the forelimbs may have been used to grasp a mate during [[copulation (zoology)|copulation]].<ref name="osborn1906">{{Cite journal |last1=Osborn |first1=H. F. |author-link=Henry Fairfield Osborn |last2=Brown |first2=B. |author-link2=Barnum Brown |year=1906 |title=''Tyrannosaurus'', Upper Cretaceous carnivorous dinosaur |journal=Bulletin of the AMNH |volume=22 |issue=16 |pages=281–296 |hdl=2246/1473}}</ref> Newman (1970) suggested that the forelimbs were used to assist ''Tyrannosaurus'' in rising from a prone position.<ref name="newman1970" /> Since then, other functions have been proposed, although some scholars find them implausible.<ref name="Padian (2022)" /> [[Kevin Padian|Padian]] (2022) argued that the reduction of the arms in tyrannosaurids did not serve a particular function but was a secondary adaptation, stating that as tyrannosaurids developed larger and more powerful skulls and jaws, the arms got smaller to avoid being bitten or torn by other individuals, particularly during group feedings.<ref name="Padian (2022)">Padian K (2022). [https://www.app.pan.pl/archive/published/app67/app009212021.pdf "Why tyrannosaurid forelimbs were so short: An integrative hypothesis"] {{Webarchive|url=https://web.archive.org/web/20220518090424/https://app.pan.pl/archive/published/app67/app009212021.pdf |date=May 18, 2022 }}. ''Acta Palaeontologica Polonica'' '''67'''(1): p. 63-76</ref>
[[File:Tyrannosaur arm 104.JPG|thumb|Diagram illustrating arm anatomy]]
Another possibility is that the forelimbs held struggling prey while it was killed by the tyrannosaur's enormous jaws. This hypothesis may be supported by [[biomechanics|biomechanical]] analysis. ''T. rex'' forelimb bones exhibit extremely thick [[Bone#Structure|cortical bone]], which has been interpreted as evidence that they were developed to withstand heavy loads. The [[biceps brachii]] muscle of an adult ''T. rex'' was capable of lifting {{convert|199|kg|lb|0}} by itself; other muscles such as the [[brachialis]] would work along with the biceps to make elbow flexion even more powerful. The [[M. biceps]] muscle of ''T.&nbsp;rex'' was 3.5 times as powerful as the [[human equivalent]]. A ''T. rex'' forearm had a limited range of motion, with the shoulder and elbow joints allowing only 40 and 45 degrees of motion, respectively. In contrast, the same two joints in ''[[Deinonychus]]'' allow up to 88 and 130 degrees of motion, respectively, while a human arm can rotate 360 degrees at the shoulder and move through 165 degrees at the elbow. The heavy build of the arm bones, strength of the muscles, and limited range of motion may indicate a system evolved to hold fast despite the stresses of a struggling prey animal. In the first detailed scientific description of ''Tyrannosaurus'' forelimbs, paleontologists Kenneth Carpenter and Matt Smith dismissed notions that the forelimbs were useless or that ''Tyrannosaurus'' was an obligate scavenger.<ref name="carpentersmith2001">{{Cite book |title=Mesozoic vertebrate life |last1=Carpenter |first1=K. |last2=Smith |first2=M. |publisher=Indiana University Press |year=2001 |isbn=978-0-253-33907-2 |editor-last=Tanke |editor-first=D. H. |editor-link=Darren Tanke |location=Bloomington |pages=[https://archive.org/details/mesozoicvertebra0000unse/page/90 90–116] |chapter=Forelimb Osteology and Biomechanics of ''Tyrannosaurus rex'' |author-link=Kenneth Carpenter |editor-last2=Carpenter |editor-first2=K. |editor-link2=Kenneth Carpenter |chapter-url=https://archive.org/details/mesozoicvertebra0000unse/page/90}}</ref>

The idea that the arms served as weapons when hunting prey have also been proposed by [[Steven M. Stanley]], who suggested that the arms were used for slashing prey, especially by using the claws to rapidly inflict long, deep gashes to its prey.<ref>{{cite magazine |url=https://news.nationalgeographic.com/2017/11/tyrannosaurus-rex-arms-weapons-paleontology-science/ |archive-url=https://web.archive.org/web/20171102164511/https://news.nationalgeographic.com/2017/11/tyrannosaurus-rex-arms-weapons-paleontology-science/ |url-status=dead |archive-date=November 2, 2017 |title=T. Rex's Tiny Arms May Have Been Vicious Weapons |last=Pickrell |first=J. |date=November 2, 2017 |magazine=National Geographic |access-date=December 10, 2018}}</ref> This was dismissed by Padian, who argued that Stanley based his conclusion on incorrectly estimated forelimb size and range of motion.<ref name="Padian (2022)" />

===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>

===Soft tissue===
[[File:Tyrannosaurus peptides.jpg|thumb|upright|''T.&nbsp;rex'' femur (MOR 1125) from which demineralized matrix and [[peptides]] (insets) were obtained]]
In the March 2005 issue of ''[[Science (journal)|Science]]'', [[Mary Higby Schweitzer]] of [[North Carolina State University]] and colleagues announced the recovery of soft tissue from the marrow cavity of a fossilized leg bone from a ''T. rex''. The bone had been intentionally, though reluctantly, broken for shipping and then not preserved in the normal manner, specifically because Schweitzer was hoping to test it for soft tissue.<ref name="smithsonian-fields">{{Cite magazine |last=Fields |first=H. |date=2006 |title=Dinosaur Shocker |url=http://www.smithsonianmag.com/science-nature/10021606.html |magazine=[[Smithsonian Magazine]] |access-date=October 2, 2008 |archive-date=October 14, 2008 |archive-url=https://web.archive.org/web/20081014011547/http://www.smithsonianmag.com/science-nature/10021606.html  }}</ref> Designated as the Museum of the Rockies specimen 1125, or MOR 1125, the dinosaur was previously excavated from the [[Hell Creek Formation]]. Flexible, bifurcating [[blood vessel]]s and fibrous but elastic [[bone]] matrix tissue were recognized. In addition, microstructures resembling [[blood cell]]s were found inside the matrix and vessels. The structures bear resemblance to [[ostrich]] blood cells and vessels. Whether an unknown process, distinct from normal fossilization, preserved the material, or the material is original, the researchers do not know, and they are careful not to make any claims about preservation.<ref name="MHSetalb">{{Cite journal |last1=Schweitzer |first1=M. H. |last2=Wittmeyer |first2=J. L. |last3=Horner |first3=J. R. |last4=Toporski |first4=J. K. |s2cid=30456613 |date=2005 |title=Soft-tissue vessels and cellular preservation in ''Tyrannosaurus rex'' |journal=[[Science (journal)|Science]] |volume=307 |issue=5717 |pages=1952–5 |bibcode=2005Sci...307.1952S |doi=10.1126/science.1108397 |pmid=15790853 |author-link=Mary Higby Schweitzer}}</ref> If it is found to be original material, any surviving proteins may be used as a means of indirectly guessing some of the DNA content of the dinosaurs involved, because each protein is typically created by a specific gene. The absence of previous finds may be the result of people assuming preserved tissue was impossible, therefore not looking. Since the first, two more tyrannosaurs and a hadrosaur have also been found to have such tissue-like structures.<ref name="smithsonian-fields" /> Research on some of the tissues involved has suggested that birds are closer relatives to tyrannosaurs than other modern animals.<ref>{{Cite news |url=http://news.bbc.co.uk/2/hi/science/nature/6548719.stm |title=Protein links T. rex to chickens |last=Rincon |first=P. |date=April 12, 2007 |work=[[BBC News]] |access-date=October 2, 2008 |archive-date=September 7, 2018 |archive-url=https://web.archive.org/web/20180907082950/http://news.bbc.co.uk/2/hi/science/nature/6548719.stm |url-status=live }}</ref> The original endogenous chemistry was also found in MOR 1125 based on preservation of elements associated with bone remodeling and redeposition (sulfur, calcium, zinc), which showed that the bone cortices are similar to those of extant birds.<ref>{{Cite journal|last1=Anné |first1=J. |last2=Canoville |first2=A. |last3=Edwards |first3=N. P. |last4=Schweitzer |first4=M. H. |last5=Zanno |first5=L. E. |title=Independent Evidence for the Preservation of Endogenous Bone Biochemistry in a Specimen of ''Tyrannosaurus rex'' |year=2023 |journal=Biology |volume=12 |issue=2 |at=264 |doi=10.3390/biology12020264 |pmid=36829540 |pmc=9953530 |doi-access=free }}</ref>

In studies reported in ''Science'' in April 2007, Asara and colleagues concluded that seven traces of [[collagen]] proteins detected in purified ''T. rex'' bone most closely match those reported in [[chicken]]s, followed by frogs and newts. The discovery of proteins from a creature tens of millions of years old, along with similar traces the team found in a mastodon bone at least 160,000 years old, upends the conventional view of fossils and may shift paleontologists' focus from bone hunting to biochemistry. Until these finds, most scientists presumed that fossilization replaced all living tissue with inert minerals. Paleontologist Hans Larsson of McGill University in Montreal, who was not part of the studies, called the finds "a milestone", and suggested that dinosaurs could "enter the field of molecular biology and really slingshot paleontology into the modern world".<ref>{{Cite news |url=https://www.usatoday.com/tech/science/discoveries/2007-04-12-trex-protein_N.htm |title=Yesterday's T. Rex is today's chicken |last=Vergano |first=D. |date=April 13, 2007 |work=[[USA Today]] |access-date=October 8, 2008 |archive-date=April 19, 2012 |archive-url=https://web.archive.org/web/20120419005821/http://www.usatoday.com/tech/science/discoveries/2007-04-12-trex-protein_N.htm |url-status=live }}</ref>

The presumed soft tissue was called into question by Thomas Kaye of the [[University of Washington]] and his co-authors in 2008. They contend that what was really inside the tyrannosaur bone was slimy [[biofilm]] created by bacteria that coated the voids once occupied by blood vessels and cells.<ref>{{Cite journal |last1=Kaye |first1=T. G. |last2=Gaugler |first2=G. |last3=Sawlowicz |first3=Z. |date=2008 |editor-last=Stepanova |editor-first=A. |title=Dinosaurian Soft Tissues Interpreted as Bacterial Biofilms |journal=PLOS ONE |volume=3 |issue=7 |pages=e2808 |bibcode=2008PLoSO...3.2808K |doi=10.1371/journal.pone.0002808 |pmc=2483347 |pmid=18665236|doi-access=free }}</ref> The researchers found that what previously had been identified as remnants of blood cells, because of the presence of iron, were actually [[framboid]]s, microscopic mineral spheres bearing iron. They found similar spheres in a variety of other fossils from various periods, including an [[ammonite]]. In the ammonite, they found the spheres in a place where the iron they contain could not have had any relationship to the presence of blood.<ref>{{Cite press release |title=New Research Challenges Notion That Dinosaur Soft Tissues Still Survive |date=July 24, 2008 |publisher=Newswise |url=http://newswise.com/articles/view/542898/ |access-date=October 8, 2008 |archive-date=July 30, 2017 |archive-url=https://web.archive.org/web/20170730134938/http://newswise.com/articles/view/542898/ |url-status=live }}</ref> Schweitzer has strongly criticized Kaye's claims and argues that there is no reported evidence that biofilms can produce branching, hollow tubes like those noted in her study.<ref>{{Cite press release |title=Researchers Debate: Is It Preserved Dinosaur Tissue, or Bacterial Slime? |date=July 30, 2008 |publisher=Discover |url=http://blogs.discovermagazine.com/80beats/2008/07/30/researchers-debate-is-it-preserved-dinosaur-tissue-or-bacterial-slime/ |access-date=September 4, 2008 |archive-date=August 7, 2008 |archive-url=https://web.archive.org/web/20080807005940/http://blogs.discovermagazine.com/80beats/2008/07/30/researchers-debate-is-it-preserved-dinosaur-tissue-or-bacterial-slime/  }}</ref> San Antonio, Schweitzer and colleagues published an analysis in 2011 of what parts of the collagen had been recovered, finding that it was the inner parts of the collagen coil that had been preserved, as would have been expected from a long period of protein degradation.<ref>{{Cite journal |last1=San Antonio |first1=J. D. |last2=Schweitzer |first2=M. H. |last3=Jensen |first3=S. T. |last4=Kalluri |first4=R. |last5=Buckley |first5=M. |last6=Orgel |first6=J. P. R. O. |date=2011 |editor-last=Van Veen |editor-first=H. W. |title=Dinosaur Peptides Suggest Mechanisms of Protein Survival |journal=PLOS ONE |volume=6 |issue=6 |pages=e20381 |bibcode=2011PLoSO...620381S |doi=10.1371/journal.pone.0020381 |pmc=3110760 |pmid=21687667|doi-access=free }}</ref> Other research challenges the identification of soft tissue as biofilm and confirms finding "branching, vessel-like structures" from within fossilized bone.<ref>{{Cite journal |last1=Peterson |first1=J. E. |last2=Lenczewski |first2=M. E. |last3=Scherer |first3=R. P. |date=October 12, 2010 |title=Influence of Microbial Biofilms on the Preservation of Primary Soft Tissue in Fossil and Extant Archosaurs |journal=PLOS ONE |volume=5 |issue=10 |pages=e13334 |bibcode=2010PLoSO...513334P |doi=10.1371/journal.pone.0013334 |pmc=2953520 |pmid=20967227 |quote=[T]he interpretation of preserved organic remains as microbial biofilm [is] highly unlikely|doi-access=free }}</ref>

===Speed===
{{Annotated image/Skeletal anatomy of T rex right leg | float=left}}
Scientists have produced a wide range of possible maximum running speeds for ''Tyrannosaurus'': mostly around {{convert|9|m/s|km/h mph|sp=us}}, but as low as {{convert|4.5|–|6.8|m/s|km/h mph|sp=us}} and as high as {{convert|20|m/s|km/h mph|sp=us}}, though it running this speed is very unlikely. ''Tyrannosaurus'' was a bulky and heavy carnivore so it is unlikely to run very fast at all compared to other theropods like ''[[Carnotaurus]]'' or ''[[Giganotosaurus]]''.<ref name="HutchinsonGarcia2002TrexSlow">{{Cite journal |last1=Hutchinson |first1=J. R. |last2=Garcia |first2=M. |s2cid=4389633 |date=2002 |title=''Tyrannosaurus'' was not a fast runner |journal=Nature |volume=415 |issue=6875 |pages=1018–21 |bibcode=2002Natur.415.1018H |doi=10.1038/4151018a |pmid=11875567 |url=http://researchonline.rvc.ac.uk/id/eprint/1204/ |archive-date=August 9, 2022 |access-date=January 23, 2023 |archive-url=https://web.archive.org/web/20220809012102/https://researchonline.rvc.ac.uk/id/eprint/1204/ |url-status=live }}</ref> Researchers have relied on various estimating techniques because, while there are many [[trackway|tracks]] of large theropods walking, none showed evidence of running.<ref name="Hutchinson2004">{{Cite journal |last=Hutchinson |first=J. R. |year=2004 |title=Biomechanical Modeling and Sensitivity Analysis of Bipedal Running Ability. II. Extinct Taxa |url=http://www.rvc.ac.uk/AboutUs/Staff/jhutchinson/documents/JRH13.pdf  |journal=Journal of Morphology |volume=262 |issue=1 |pages=441–461 |doi=10.1002/jmor.10240 |pmid=15352202 |s2cid=15677774 |archive-url=https://web.archive.org/web/20081031093050/http://www.rvc.ac.uk/AboutUs/Staff/jhutchinson/documents/JRH13.pdf |archive-date=October 31, 2008}}</ref>

A 2002 report used a mathematical model (validated by applying it to three living animals: [[alligator]]s, [[chicken]]s, and [[human]]s; and eight more species, including emus and ostriches<ref name="Hutchinson2004" />) to gauge the leg muscle mass needed for fast running (over {{convert|40|km/h|mph|disp=or|abbr=on}}).<ref name="HutchinsonGarcia2002TrexSlow" /> Scientists who think that ''Tyrannosaurus'' was able to run point out that hollow bones and other features that would have lightened its body may have kept adult weight to a mere {{convert|4.5|MT|ST}} or so, or that other animals like [[ostrich]]es and [[horse]]s with long, flexible legs are able to achieve high speeds through slower but longer strides.<ref name="Hutchinson2004" /> Proposed top speeds exceeded {{convert|40|km/h|mph|sp=us}} for ''Tyrannosaurus'', but were deemed infeasible because they would require exceptional leg muscles of approximately 40–86%&nbsp;of total body mass. Even moderately fast speeds would have required large leg muscles. If the muscle mass was less, only {{convert|18|km/h|mph|sp=us}} for walking or jogging would have been possible.<ref name="HutchinsonGarcia2002TrexSlow" /> Holtz noted that tyrannosaurids and some closely related groups had significantly longer [[distal]] hindlimb components (shin plus foot plus toes) relative to the femur length than most other theropods, and that tyrannosaurids and their close relatives had a tightly interlocked [[metatarsus]] (foot bones).<ref name="Holtz1998TaxonomyCoelurosauria">{{Cite journal |last=Holtz |first=T. R. |author-link=Thomas R. Holtz Jr. |date=May 1, 1996 |title=Phylogenetic taxonomy of the Coelurosauria (Dinosauria; Theropoda) |url=http://jpaleontol.geoscienceworld.org/cgi/content/abstract/70/3/536 |journal=[[Journal of Paleontology]] |volume=70 |issue=3 |pages=536–538 |doi=10.1017/S0022336000038506 |bibcode=1996JPal...70..536H |s2cid=87599102 |access-date=October 3, 2008 |archive-date=October 26, 2008 |archive-url=https://web.archive.org/web/20081026053239/http://jpaleontol.geoscienceworld.org/cgi/content/abstract/70/3/536 |url-status=live }}</ref> The third metatarsal was squeezed between the second and fourth metatarsals to form a single unit called an [[arctometatarsal|arctometatarsus]]. This ankle feature may have helped the animal to run more efficiently.<ref>{{Cite book |url=https://books.google.com/books?id=VThUUUtM8A4C&q=tyrannosaurus+metatarsals+squeezing&pg=PA193 |title=Vertebrate Palaeontology |last=Benton |first=M. |year=2014 |isbn=978-1-118-40755-4 |edition=4th |page=193|publisher=John Wiley & Sons }}</ref> Together, these leg features allowed ''Tyrannosaurus'' to transmit locomotory forces from the foot to the lower leg more effectively than in earlier theropods.<ref name="Holtz1998TaxonomyCoelurosauria" />  
[[File:Tyrannosaurid trackway.png|thumb|Only known tyrannosaurid trackway (''[[Bellatoripes fredlundi]]''), from the [[Wapiti Formation]], [[British Columbia]]]]

Additionally, a 2020 study indicates that ''Tyrannosaurus'' and other tyrannosaurids were exceptionally efficient walkers. Studies by Dececchi et al., compared the leg proportions, body mass, and the gaits of more than 70 species of theropod dinosaurs including ''Tyrannosaurus'' and its relatives. The research team then applied a variety of methods to estimate each dinosaur's top speed when running as well as how much energy each dinosaur expended while moving at more relaxed speeds such as when walking. Among smaller to medium-sized species such as dromaeosaurids, longer legs appear to be an adaptation for faster running, in line with previous results by other researchers. But for theropods weighing over {{convert|1000|kg|lb|abbr=on}}, top running speed is limited by body size, so longer legs instead were found to have correlated with low-energy walking. The results further indicate that smaller theropods evolved long legs as a means to both aid in hunting and escape from larger predators while larger theropods that evolved long legs did so to reduce the energy costs and increase foraging efficiency, as they were freed from the demands of predation pressure due to their role as apex predators. Compared to more basal groups of theropods in the study, tyrannosaurs like ''Tyrannosaurus'' itself showed a marked increase in foraging efficiency due to reduced energy expenditures during hunting or scavenging. This in turn likely resulted in tyrannosaurs having a reduced need for hunting forays and requiring less food to sustain themselves as a result. Additionally, the research, in conjunction with studies that show tyrannosaurs were more agile than other large-bodied theropods, indicates they were quite well-adapted to a long-distance stalking approach followed by a quick burst of speed to go for the kill. Analogies can be noted between tyrannosaurids and modern wolves as a result, supported by evidence that at least some tyrannosaurids were hunting in group settings.<ref>{{Cite journal|title=The fast and the frugal: Divergent locomotory strategies drive limb lengthening in theropod dinosaurs |first1=T. Alexander |last1=Dececchi |first2=Aleksandra M. |last2=Mloszewska |first3=Thomas R. Jr. |last3=Holtz |first4=Michael B. |last4=Habib |first5=Hans C. E. |last5=Larsson |date=May 13, 2020 |journal=PLOS ONE |volume=15 |issue=5 |pages=e0223698 |doi=10.1371/journal.pone.0223698 |pmid=32401793 |pmc=7220109 |bibcode = 2020PLoSO..1523698D |doi-access=free}}</ref><ref>{{cite news |title=T. rex was a champion walker, super-efficient at lower speeds |url=https://www.eurekalert.org/news-releases/500578 |access-date=August 16, 2023 |work=EurekAlert! |date=May 13, 2020 |language=en |archive-date=August 16, 2023 |archive-url=https://web.archive.org/web/20230816101705/https://www.eurekalert.org/news-releases/500578 |url-status=live }}</ref>

A study published in 2021 by Pasha van Bijlert et al., calculated the [[preferred walking speed]] of ''Tyrannosaurus'', reporting a speed of {{convert|1.28|m/s|km/h mph|sp=us}}. While walking, animals reduce their [[cost of transport|energy expenditure]] by choosing certain step rhythms at which their body parts [[resonate]]. The same would have been true for [[dinosaurs]], but previous studies did not fully account for the impact the tail had on their walking speeds. According to the authors, when a dinosaur walked, its tail would slightly sway up and down with each step as a result of the [[interspinous ligaments]] suspending the tail. Like rubber bands, these ligaments stored energy when they are stretched due to the swaying of the tail. Using a 3-D model of ''Tyrannosaurus'' specimen [[Trix (dinosaur)|Trix]], muscles and ligaments were reconstructed to simulate the tail movements. This results in a rhythmic, energy-efficient walking speed for ''Tyrannosaurus'' similar to that seen in living animals such as humans, ostriches and giraffes.<ref name=vanBijlert2021>{{cite journal |author1=van Bijlert, P. A. |author2=van Soest, A. J. K. |author3=Schulp, A. S. |title=Natural Frequency Method: estimating the preferred walking speed of ''Tyrannosaurus rex'' based on tail natural frequency. |journal=Royal Society Open Science |volume=8 |issue=4 |page=201441 |year=2021 |doi=10.1098/rsos.201441 |pmid=33996115 |pmc=8059583 |bibcode=2021RSOS....801441V |s2cid=233312053 |url=https://phys.org/news/2021-04-dinosaur-biomechanical-tyrannosaurus-rex-gait.html |archive-date=April 22, 2021 |access-date=April 22, 2021 |archive-url=https://web.archive.org/web/20210422224520/https://phys.org/news/2021-04-dinosaur-biomechanical-tyrannosaurus-rex-gait.html |url-status=live }}</ref>

A 2017 study estimated the top running speed of ''Tyrannosaurus'' as {{convert|17|mph|km/h|abbr=on}}, speculating that ''Tyrannosaurus'' exhausted its energy reserves long before reaching top speed, resulting in a parabola-like relationship between size and speed.<ref>{{Cite web |url=https://www.sciencedaily.com/releases/2017/07/170717115657.htm |title=Why ''Tyrannosaurus'' was a slow runner and why the largest are not always the fastest |date=July 17, 2017 |website=ScienceDaily |language=en |access-date=November 10, 2017 |archive-date=April 2, 2019 |archive-url=https://web.archive.org/web/20190402111657/https://www.sciencedaily.com/releases/2017/07/170717115657.htm |url-status=live }}</ref><ref>{{Cite journal |last1=Hirt |first1=M. R. |last2=Jetz |first2=W. |last3=Rall |first3=B. C. |last4=Brose |first4=U. |s2cid=425473 |date=2017 |title=A general scaling law reveals why the largest animals are not the fastest. |journal=Nature Ecology & Evolution |volume=1 |issue=8 |pages=1116–1122 |doi=10.1038/s41559-017-0241-4 |pmid=29046579|bibcode=2017NatEE...1.1116H }}</ref> Another 2017 study hypothesized that an adult ''Tyrannosaurus'' was incapable of running due to high skeletal loads. Using a calculated weight estimate of 7&nbsp;tons, the model showed that speeds above {{convert|11|mph|km/h|abbr=on}} would have probably shattered the leg bones of ''Tyrannosaurus''. The finding may mean that running was also not possible for other giant theropod dinosaurs like ''[[Giganotosaurus]]'', ''[[Mapusaurus]]'' and ''[[Acrocanthosaurus]]''.<ref>{{Cite journal |last1=Sellers |first1=W. I. |last2=Pond |first2=S. B. |last3=Brassey |first3=C. A. |last4=Manning |first4=P. L. |last5=Bates |first5=K. T. |date=July 18, 2017 |title=Investigating the running abilities of ''Tyrannosaurus rex'' using stress-constrained multibody dynamic analysis |journal=PeerJ |language=en |volume=5 |pages=e3420 |doi=10.7717/peerj.3420 |issn=2167-8359 |pmc=5518979 |pmid=28740745 |doi-access=free }}</ref>
However, studies by Eric Snively and colleagues'','' published in 2019 indicate that ''Tyrannosaurus'' and other tyrannosaurids were more maneuverable than allosauroids and other theropods of comparable size due to low rotational inertia compared to their body mass combined with large leg muscles. As a result, it is hypothesized that ''Tyrannosaurus'' was capable of making relatively quick turns and could likely pivot its body more quickly when close to its prey, or that while turning, the theropod could "pirouette" on a single planted foot while the alternating leg was held out in a suspended swing during a pursuit. The results of this study potentially could shed light on how agility could have contributed to the success of tyrannosaurid evolution.<ref>{{Cite journal |last1=Cotton |first1=J. R. |last2=Hartman |first2=S. A. |last3=Currie |first3=P. J. |last4=Witmer |first4=L. M. |last5=Russell |first5=A. P. |last6=Holtz |first6=T. R. Jr. |last7=Burns |first7=M. E. |last8=Surring |first8=L. A. |last9=Mallison |first9=H. |date=February 21, 2019 |title=Lower rotational inertia and larger leg muscles indicate more rapid turns in tyrannosaurids than in other large theropods |journal=PeerJ |volume=7 |pages=e6432 |doi=10.7717/peerj.6432 |pmid=30809441 |pmc=6387760 |first10=D. M. |last10=Henderson |first11=H. |last11=O'Brien |first12=E. |last12=Snively |doi-access=free }}</ref>

===Possible footprints===
[[File:T. rex rising (Caneer et.al. 2021).png|thumb|Depiction of ''Tyrannosaurus'' rising from the ground, based on fossil tracks described in 2021.]]
Rare fossil footprints and trackways found in New Mexico and Wyoming that are assigned to the ichnogenus ''[[Tyrannosauripus]]'' have been attributed to being made by ''Tyrannosaurus'', based on the stratigraphic age of the rocks they are preserved in. The first specimen, found in 1994 was described by Lockley and Hunt and consists of a single, large footprint. Another pair of ichnofossils, described in 2021, show a large tyrannosaurid rising from a prone position by rising up using its elbows in conjunction with the pads on their feet to stand. These two unique sets of fossils were found in Ludlow, Colorado and Cimarron, New Mexico.<ref>{{cite journal|url=https://www.researchgate.net/publication/348002331|last1=Caneer|first1=T.|last2=Molkestad|first2=T.|last3=Lucas|first3=S.G.|title=TRACKS IN THE UPPER CRETACEOUS OF THE RATON BASIN POSSIBLY SHOW TYRANNOSAURID RISING FROM A PRONE POSITION|journal=New Mexico Museum of Natural History and Science|year=2021|pages=29–37}}</ref> Another ichnofossil described in 2018, perhaps belonging to a juvenile ''Tyrannosaurus'' or the dubious genus ''Nanotyrannus'' was uncovered in the Lance Formation of Wyoming. The trackway itself offers a rare glimpse into the walking speed of tyrannosaurids, and the trackmaker is estimated to have been moving at a speed of {{convert|4.5-8.0|km/h|mph|sp=us}}, significantly faster than previously assumed for estimations of walking speed in tyrannosaurids.<ref>{{cite journal|url=https://www.sciencedirect.com/science/article/abs/pii/S0195667115301452|last1=Smith|first1=S.D|last2=Persons|first2=W.S.|last3=Xing|first3=Lida|title=A tyrannosaur trackway at Glenrock, Lance Formation (Maastrichtian), Wyoming|year=2016|journal=Cretaceous Research|volume=61|pages=1–4|doi=10.1016/j.cretres.2015.12.020|bibcode=2016CrRes..61....1S|archive-date=April 22, 2021|access-date=January 3, 2021|archive-url=https://web.archive.org/web/20210422134259/https://www.sciencedirect.com/science/article/abs/pii/S0195667115301452|url-status=live}}</ref><ref>{{cite journal|url=http://westerndigs.org/tyrannosaur-tracks-discovered-in-wyoming-reveal-dinosaurs-speed/|title=Tyrannosaur Tracks Discovered in Wyoming Reveal Dinosaur's Speed|last=De Pastino|first=B.|journal=Western Digs|year=2016|volume=61|pages=1–4|doi=10.1016/j.cretres.2015.12.020|bibcode=2016CrRes..61....1S|access-date=January 3, 2021|archive-date=January 18, 2021|archive-url=https://web.archive.org/web/20210118041135/http://westerndigs.org/tyrannosaur-tracks-discovered-in-wyoming-reveal-dinosaurs-speed/}}</ref>

=== Brain and senses ===
[[File:Sue TRex Skull Full Frontal.JPG|thumb|upright|left|The eye-sockets faced mainly forwards, giving it good [[binocular vision]] ([[Sue specimen]]).]]
A study conducted by [[Lawrence Witmer]] and Ryan Ridgely of Ohio University found that ''Tyrannosaurus'' shared the heightened sensory abilities of other [[coelurosaur]]s, highlighting relatively rapid and coordinated eye and head movements; an enhanced ability to sense low frequency sounds, which would allow tyrannosaurs to track prey movements from long distances; and an enhanced sense of smell.<ref name="witmer2009">{{Cite journal |last1=Witmer |first1=L. M. |last2=Ridgely |first2=R. C. |date=2009 |title=New Insights into the Brain, Braincase, and Ear Region of Tyrannosaurs (Dinosauria, Theropoda), with Implications for Sensory Organization and Behavior |journal=The Anatomical Record |volume=292 |issue=9 |pages=1266–1296 |doi=10.1002/ar.20983 |pmid=19711459|s2cid=17978731 |doi-access=free }}</ref> A study published by Kent Stevens concluded that ''Tyrannosaurus'' had keen vision. By applying modified [[perimetry]] to facial reconstructions of several dinosaurs including ''Tyrannosaurus'', the study found that ''Tyrannosaurus'' had a binocular range of 55 degrees, surpassing that of modern hawks. Stevens estimated that ''Tyrannosaurus'' had 13 times the visual acuity of a human and surpassed the visual acuity of an eagle, which is 3.6 times that of a person. Stevens estimated a limiting far point (that is, the distance at which an object can be seen as separate from the horizon) as far as {{convert|6|km|mi|sp=us|abbr=on}} away, which is greater than the {{convert|1.6|km|mi|0|sp=us|abbr=on}} that a human can see.<ref name="Stevens2006Binocular"/><ref name="jaffe" /><ref name="stevenswebpage">{{Cite web |url=http://ix.cs.uoregon.edu/~kent/paleontology/binocularVision/ |title=The Binocular Vision of Theropod Dinosaurs |last=Stevens |first=K. A. |date=April 1, 2011 |access-date=July 19, 2013 |archive-date=August 19, 2018 |archive-url=https://web.archive.org/web/20180819050655/http://ix.cs.uoregon.edu/~kent/paleontology/binocularVision/ |url-status=live }}</ref>

Thomas Holtz Jr. would note that high depth perception of ''Tyrannosaurus'' may have been due to the prey it had to hunt, noting that it had to hunt ceratopsians such as ''[[Triceratops]]'', ankylosaurs such as ''[[Ankylosaurus]]'', and hadrosaurs. He would suggest that this made precision more crucial for ''Tyrannosaurus'' enabling it to, "get in, get that blow in and take it down." In contrast, ''[[Acrocanthosaurus]]'' had limited depth perception because they hunted large sauropods, which were relatively rare during the time of ''Tyrannosaurus''.<ref name="HoltzLecture2013" />

Though no ''Tyrannosaurus'' [[Scleral Ring|sclerotic ring]] has been found, [[Kenneth Carpenter]] estimated its size based on that of ''Gorgosaurus''. The inferred sclerotic ring for the [[Stan (dinosaur)|Stan specimen]] is ~{{convert|7|cm|in|abbr=on|sp=us}} in diameter with an internal aperture diameter of ~{{convert|3.5|cm|in|abbr=on|sp=us}}. Based on eye proportions in living reptiles, this implies a pupil diameter of about {{convert|2.5|cm|in|abbr=on|sp=us}}, an iris diameter about that of the sclerotic ring, and an eyeball diameter of {{convert|11-12|cm|in|abbr=on|sp=us}}. Carpenter also estimated an eyeball depth of ~{{convert|7.7-9.6|cm|in|abbr=on|sp=us}}. Based on these calculations, the [[f-number]] for Stan's eye is 3–3.8; since [[Diurnality|diurnal]] animals have f-numbers of 2.1 or higher, this would indicate that ''Tyrannosaurus'' had poor low-light vision and hunted during the day.<ref name="Trexpaleobiologychapter14">{{cite book|author=Carpenter, K.|chapter=A Closer Look at the Scavenging versus Predation by ''Tyrannosaurus rex''|title=Tyrannosaurid Paleobiology |year=2013 |publisher=Indiana University Press |isbn=978-0-253-00930-2 |editor-last=Parrish |editor-first=M. J. |editor-last2=Molnar |editor-first2=R. E. |editor-last3=Currie |editor-first3=P. J. |editor-last4=Koppelhus |editor-first4=E. B. |series=Life of the Past |location=Bloomington (Ind.) |pages=265–278 }}</ref>

''Tyrannosaurus'' had very large [[olfactory bulb]]s and [[olfactory nerve]]s relative to their brain size, the organs responsible for a heightened sense of smell. This suggests that the sense of smell was highly developed, and implies that tyrannosaurs could detect carcasses by scent alone across great distances. The sense of smell in tyrannosaurs may have been comparable to modern [[vulture]]s, which use scent to track carcasses for scavenging. Research on the olfactory bulbs has shown that ''T. rex'' had the most highly developed sense of smell of 21 sampled non-avian dinosaur species.<ref name="Calgary Herald">{{cite news |url=http://www.canada.com/calgaryherald/story.html?id=3641f27e-ca2e-44e8-a56b-f9a0b4aef4b5 |title=''T. Rex'' brain study reveals a refined 'nose' |date=October 28, 2008 |newspaper=Calgary Herald |access-date=October 29, 2008 |archive-date=December 6, 2008 |archive-url=https://web.archive.org/web/20081206065850/http://www.canada.com/calgaryherald/story.html?id=3641f27e-ca2e-44e8-a56b-f9a0b4aef4b5 |url-status=live }}</ref>
[[File:Tyrannosaurus brain aus.jpg|thumb|Cast of the braincase at the [[Australian Museum]], Sydney.]]
Somewhat unusually among theropods, ''T.&nbsp;rex'' had a very long [[cochlea]]. The length of the cochlea is often related to hearing acuity, or at least the importance of hearing in behavior, implying that hearing was a particularly important sense to tyrannosaurs. Specifically, data suggests that ''T. rex'' heard best in the low-frequency range, and that low-frequency sounds were an important part of tyrannosaur behavior.<ref name="witmer2009" /> A 2017 study by Thomas Carr and colleagues found that the snout of tyrannosaurids was highly sensitive, based on a high number of small openings in the facial bones of the related ''Daspletosaurus'' that contained [[sensory neuron]]s. The study speculated that tyrannosaurs might have used their sensitive snouts to measure the temperature of their nests and to gently pick up eggs and hatchlings, as seen in modern crocodylians.<ref name="carr2017" /> 
Another study published in 2021 further suggests that ''Tyrannosaurus'' had an acute sense of touch, based on neurovascular canals in the front of its jaws, which it could utilize to better detect and consume prey. The study, published by Kawabe and Hittori et al., suggests that ''Tyrannosaurus'' could also accurately sense slight differences in material and movement, allowing it to utilize different feeding strategies on different parts of its prey's carcasses depending on the situation. The sensitive neurovascular canals of ''Tyrannosaurus'' also likely were adapted to performing fine movements and behaviors such as nest building, parental care, and other social behavior such as intraspecific communication. The results of this study also align with results made in studying the related tyrannosaurid ''[[Daspletosaurus horneri]]'' and the [[allosauroid]] ''[[Neovenator]]'', which have similar neurovascular adaptations, suggesting that the faces of theropods were highly sensitive to pressure and touch.<ref>{{Cite journal|doi=10.1080/08912963.2021.1965137|title=Complex neurovascular system in the dentary of Tyrannosaurus|year=2021|last1=Kawabe|first1=Soichiro|last2=Hattori|first2=Soki|journal=Historical Biology|volume=34 |issue=7 |pages=1137–1145|doi-access=free|bibcode=2022HBio...34.1137K }}</ref><ref>{{Cite web|url=https://phys.org/news/2021-08-rex-jaw-sensors-fearsome-predator.html|title=T. rex's jaw had sensors that made it an even more fearsome predator|website=phys.org|access-date=August 23, 2021|archive-date=August 23, 2021|archive-url=https://web.archive.org/web/20210823232627/https://phys.org/news/2021-08-rex-jaw-sensors-fearsome-predator.html|url-status=live}}</ref> However, a more recent study reviewing the evolution of the trigeminal canals among sauropsids notes that a much denser network of neurovascular canals in the snout and lower jaw is more commonly encountered in aquatic or semiaquatic taxa (e.g., ''[[Spinosaurus]]'', ''[[Halszkaraptor]]'', ''[[Plesiosaurus]]''), and taxa that developed a rhamphotheca (e.g., ''[[Caenagnathasia]]''), while the network of canals in ''Tyrannosaurus'' appears simpler, though still more derived than in most ornithischians, and overall  
terrestrial taxa such as tyrannosaurids and ''Neovenator'' may have had average facial sensitivity for non-edentulous terrestrial theropods, although further research is needed. The neurovascular canals in ''Tyrannosaurus'' may instead have supported soft tissue structures for thermoregulation or social signaling, the latter of which could be confirmed by the fact that the neurovascular network of canals may have changed during ontogeny.<ref>{{Cite journal|last=Benoit|first=Florian Bouabdellah, Emily Lessner, and Julien|date=January 20, 2022|title=The rostral neurovascular system of Tyrannosaurus rex|url=https://palaeo-electronica.org/content/2022/3518-t-rex-trigeminal-canals|journal=Palaeontologia Electronica|language=English|volume=25|issue=1|pages=1–20|doi=10.26879/1178|s2cid=246204236|issn=1094-8074|doi-access=free|archive-date=March 16, 2022|access-date=January 22, 2022|archive-url=https://web.archive.org/web/20220316214524/https://palaeo-electronica.org/content/2022/3518-t-rex-trigeminal-canals|url-status=live}}</ref>

A study by Grant R. Hurlburt, Ryan C. Ridgely and Lawrence Witmer obtained estimates for [[Encephalization Quotient]]s (EQs), based on reptiles and birds, as well as estimates for the ratio of cerebrum to brain mass. The study concluded that ''Tyrannosaurus'' had the relatively largest brain of all adult non-avian dinosaurs with the exception of certain small maniraptoriforms (''[[Bambiraptor]]'', ''[[Troodon]]'' and ''[[Ornithomimus]]''). The study found that ''Tyrannosaurus'''s relative brain size was still within the range of modern reptiles, being at most 2 [[standard deviations]] above the mean of non-avian reptile EQs. The estimates for the ratio of cerebrum mass to brain mass would range from 47.5 to 49.53 percent. According to the study, this is more than the lowest estimates for extant birds (44.6 percent), but still close to the typical ratios of the smallest sexually mature alligators which range from 45.9–47.9 percent.<ref name="Trexpaleobiologychapter6">{{Cite book |title=Tyrannosaurid Paleobiology |last1=Hurlburt |first1=G. S. |last2=Ridgely |first2=R. C. |last3=Witmer |first3=L. M. |date=July 5, 2013 |publisher=Indiana University Press |isbn=978-0-253-00947-0 |pages=134–154 |chapter=Relative size of brain and cerebrum in Tyrannosaurid dinosaurs: an analysis using brain-endocast quantitative relationships in extant alligators |access-date=October 20, 2013 |editor-last=Parrish |editor-first=M. J. |editor-last2=Molnar |editor-first2=R. E. |editor-last3=Currie |editor-first3=P. J. |editor-last4=Koppelhus |editor-first4=E. B. |chapter-url=https://www.researchgate.net/publication/256536375}}</ref> Other studies, such as those by Steve Brusatte, indicate the encephalization quotient of ''Tyrannosaurus'' was similar in range (2.0–2.4) to a [[chimpanzee]] (2.2–2.5), though this may be debatable as reptilian and mammalian encephalization quotients are not equivalent.<ref>{{cite book|last=Brusatten|first=Steve|title=The Rise and Fall of the Dinosaurs|date=2018|publisher=HarperCollins Publishers|location=New York, New York|isbn=978-0-06-249043-8|page=219}}</ref>

=== Social behavior ===
[[File:Tyrannosaurus Growth Series LACM.jpg|left|thumb|Mounted skeletons of different age groups (skeleton in lower left based on the juvenile formerly named ''Stygivenator''), [[Natural History Museum of Los Angeles County]]]]
[[Philip J. Currie]] suggested that Tyrannosaurus may have been [[pack hunter]]s, comparing ''T. rex'' to related species ''[[Tarbosaurus bataar]]'' and ''[[Albertosaurus sarcophagus]]'', citing fossil evidence that may indicate [[Sociality|gregarious]] (describing animals that travel in herds or packs) behavior.<ref name="discoverdinogangs">{{cite web|date=June 22, 2011|title=Dino Gangs|url=http://www.discoveryuk.com/the-loop/dino-gangs/|archive-url=https://web.archive.org/web/20120119125039/http://www.discoveryuk.com/the-loop/dino-gangs/|archive-date=January 19, 2012|access-date=January 19, 2012|website=Discovery Channel}}</ref> A find in [[South Dakota]] where three ''T. rex'' skeletons were in close proximity may suggest the formation of a pack.<ref name="tgraphpack">{{Cite news|last=Collins|first=N.|date=June 22, 2011|title=Tyrannosaurus Rex 'hunted in packs'|work=The Telegraph|url=https://www.telegraph.co.uk/news/science/dinosaurs/8589113/Tyrannosaurus-Rex-hunted-in-packs.html |archive-url=https://ghostarchive.org/archive/20220110/https://www.telegraph.co.uk/news/science/dinosaurs/8589113/Tyrannosaurus-Rex-hunted-in-packs.html |archive-date=January 10, 2022 |url-access=subscription |url-status=live|access-date=March 23, 2014}}{{cbignore}}</ref><ref name="djournal">{{Cite web|last=Wallis|first=P.|date=June 11, 2012|title=Op-Ed: T. Rex pack hunters? Scary, but likely to be true|url=http://digitaljournal.com/article/326451|access-date=December 23, 2015|website=Digitaljournal.com|archive-date=April 16, 2021|archive-url=https://web.archive.org/web/20210416141803/http://www.digitaljournal.com/article/326451|url-status=live}}</ref> Cooperative pack hunting may have been an effective strategy for subduing prey with advanced [[anti-predator adaptation]]s which pose potential lethality such as ''[[Triceratops]]'' and ''[[Ankylosaurus]]''.<ref name="discoverdinogangs" />

Currie's pack-hunting ''T. rex'' hypothesis has been criticized for not having been [[peer-review]]ed, but rather was discussed in a television interview and book called ''Dino Gangs''.<ref name="switek2011dinogangs">{{Cite web|last=Switek|first=B.|date=July 25, 2011|title=A bunch of bones doesn't make a gang of bloodthirsty tyrannosaurs|url=https://www.theguardian.com/science/blog/2011/jul/25/bunch-bones-gang-bloodthirsty-tyrannosaurs|access-date=June 21, 2015|website=The Guardian|archive-date=December 21, 2018|archive-url=https://web.archive.org/web/20181221011020/https://www.theguardian.com/science/blog/2011/jul/25/bunch-bones-gang-bloodthirsty-tyrannosaurs|url-status=live}}</ref> The Currie theory for pack hunting by ''T. rex'' is based mainly by analogy to a different species, ''Tarbosaurus bataar''. Evidence of gregariousness in ''T. bataar'' itself has not been peer-reviewed, and to Currie's own admission, can only be interpreted with reference to evidence in other closely related species. According to Currie gregariousness in ''Albertosaurus sarcophagus'' is supported by the discovery of 26 individuals with varied ages in the Dry Island bonebed. He ruled out the possibility of a predator trap due to the similar preservation state of individuals and the near absence of herbivores.<ref name="switek2011dinogangs" /><ref name="currie1998">{{cite journal|last=Currie|first=Philip J.|author-link=Philip J. Currie|year=1998|title=Possible evidence of gregarious behaviour in tyrannosaurids|url=http://www.mnhn.ul.pt/geologia/gaia/21.pdf|journal=Gaia|volume=15|pages=271–277|archive-url=https://web.archive.org/web/20090326062833/http://www.mnhn.ul.pt/geologia/gaia/21.pdf|archive-date=March 26, 2009|access-date=May 3, 2009}} (not printed until 2000)</ref>

Additional support of tyrannosaurid gregariousness can be found in fossilized [[trackway]]s from the Upper Cretaceous [[Wapiti Formation]] of northeastern [[British Columbia]], Canada, left by three tyrannosaurids traveling in the same direction.<ref name="TG-20140724">{{Cite web|last=Sample|first=I.|date=July 23, 2014|title=Researchers find first sign that tyrannosaurs hunted in packs|url=https://www.theguardian.com/science/2014/jul/23/tyrannosaurs-hunted-packs-tracks-canada|access-date=July 28, 2014|website=[[The Guardian]]|archive-date=December 15, 2018|archive-url=https://web.archive.org/web/20181215141823/https://www.theguardian.com/science/2014/jul/23/tyrannosaurs-hunted-packs-tracks-canada|url-status=live}}</ref><ref>{{Cite journal|last=McCrea|first=R. T.|year=2014|title=A 'Terror of Tyrannosaurs': The First Trackways of Tyrannosaurids and Evidence of Gregariousness and Pathology in Tyrannosauridae|journal=PLOS ONE|volume=9|issue=7|pages=e103613|bibcode=2014PLoSO...9j3613M|doi=10.1371/journal.pone.0103613|pmc=4108409|pmid=25054328|doi-access=free}}</ref> According to scientists assessing the Dino Gangs program, the evidence for pack hunting in ''Tarbosaurus'' and ''Albertosaurus'' is weak and based on group skeletal remains for which alternate explanations may apply (such as drought or a flood forcing dinosaurs to die together in one place).<ref name="switek2011dinogangs" /> Others researchers have speculated that instead of large theropod social groups, some of these finds represent behavior more akin to [[Komodo dragon]]-like mobbing of carcasses, even going as far as to say true pack-hunting behavior may not exist in any non-avian dinosaurs due to its rarity in modern predators.<ref name="roachbrinkman2007">{{cite journal|last=Roach|first=Brian T.|author2=Brinkman, Daniel T.|year=2007|title=A reevaluation of cooperative pack hunting and gregariousness in ''Deinonychus antirrhopus'' and other nonavian theropod dinosaurs|journal=Bulletin of the Peabody Museum of Natural History|volume=48|issue=1|pages=103–138|doi=10.3374/0079-032X(2007)48[103:AROCPH]2.0.CO;2|s2cid=84175628 }}</ref>

Evidence of intraspecific attack was found by Joseph Peterson and his colleagues in the juvenile ''Tyrannosaurus'' nicknamed [[Jane (dinosaur)|Jane]]. Peterson and his team found that Jane's skull showed healed puncture wounds on the upper jaw and snout which they believe came from another juvenile ''Tyrannosaurus''. Subsequent CT scans of Jane's skull would further confirm the team's hypothesis, showing that the puncture wounds came from a traumatic injury and that there was subsequent healing.<ref name="JaneFacebiting">{{Cite journal |last1=Peterson |first1=J. E. |last2=Henderson |first2=M. D. |last3=Sherer |first3=R. P. |last4=Vittore |first4=C. P. |s2cid=85602478 |date=2009 |title=Face Biting On A Juvenile Tyrannosaurid And Behavioral Implications |url=http://palaios.sepmonline.org/content/24/11/780  |journal=PALAIOS |volume=24 |issue=11 |pages=780–784 |bibcode=2009Palai..24..780P |doi=10.2110/palo.2009.p09-056r |archive-url=https://archive.today/20130811100341/http://palaios.sepmonline.org/content/24/11/780 |archive-date=August 11, 2013}}</ref> The team would also state that Jane's injuries were structurally different from the parasite-induced lesions found in Sue and that Jane's injuries were on its face whereas the parasite that infected Sue caused lesions to the lower jaw.<ref name="JaneFaceBiteWeb">{{Cite web |url=http://www.niu.edu/PubAffairs/RELEASES/2009/nov/testytrex.shtml |title=The terrible teens of ''T. rex'' NIU scientists: Young tyrannosaurs did serious battle against each other |last=Parisi |first=T. |date=November 2, 2009 |publisher=Northern Illinois University |archive-url=https://web.archive.org/web/20130814164927/http://www.niu.edu/PubAffairs/RELEASES/2009/nov/testytrex.shtml |archive-date=August 14, 2013 |access-date=August 10, 2013}}</ref> Pathologies of other ''Tyrannosaurus'' specimens have been suggested as evidence of conspecific attack, including "Wyrex" with a hole penetrating its jugual and severe trauma on its tail that shows signs of [[bone remodeling]] (not regrowth).<ref name="Trexpaleobiologychapter10">{{cite book|author=Rothschild, B.M.|chapter=Clawing Their Way to the Top: Tyrannosaurid Pathology and Lifestyle|title=Tyrannosaurid Paleobiology |year=2013 |publisher=Indiana University Press |isbn=978-0-253-00930-2 |editor-last=Parrish |editor-first=M. J. |editor-last2=Molnar |editor-first2=R. E. |editor-last3=Currie |editor-first3=P. J. |editor-last4=Koppelhus |editor-first4=E. B. |series=Life of the Past |location=Bloomington (Ind.) |pages=211–222 }}</ref><ref>{{cite journal|author1=Anné, J.|author2=Whitney, M.|author3=Brocklehurst, R.|author4=Donnelly, K.|author5=Rothschild, B.|year=2023|title=Unusual lesions seen in the caudals of the hadrosaur, ''Edmontosaurus annectens''|journal=The Anatomical Record|volume=306|issue=3|pages=594–606|doi=10.1002/ar.25078|pmid=36089756 }}</ref>

===Feeding strategies===
{{Main|Feeding behavior of Tyrannosaurus|l1=Feeding behavior of ''Tyrannosaurus''}}
[[File:Tyrannosaurus tooth marks.png|thumb|upright|''Tyrannosaurus'' tooth marks on bones of various herbivorous dinosaurs]]
[[File:Tyrannosaurus and Triceratops at Natural History Museum of Los Angeles County.jpg|thumb|A ''Tyrannosaurus'' mounted next to a ''[[Triceratops]]'' at the [[Los Angeles Natural History Museum]]]]
Most paleontologists accept that ''Tyrannosaurus'' was both an active [[predator]] and a [[scavenger]] like most large [[carnivores]].<ref name="nationalgeographic">{{cite magazine |url=https://www.nationalgeographic.com/science/phenomena/2013/07/16/time-to-slay-the-t-rex-scavenger-debate/ |title=Time to Slay the ''T. rex'' Scavenger "Debate" |date=July 16, 2013 |magazine=National Geographic |archive-url=https://web.archive.org/web/20180712030717/https://www.nationalgeographic.com/science/phenomena/2013/07/16/time-to-slay-the-t-rex-scavenger-debate/ |archive-date=July 12, 2018 }}</ref> By far the largest carnivore in its environment, ''T. rex'' was most likely an [[apex predator]], preying upon [[hadrosaur]]s, armored herbivores like [[ceratopsia]]ns and [[ankylosaur]]s, and possibly [[sauropod]]s.<ref>{{Cite journal |url=https://www.smithsonianmag.com/science-nature/when-tyrannosaurus-chomped-sauropods-67170161/ |title=When ''Tyrannosaurus'' Chomped Sauropods |last=Black |first=Riley |date=April 13, 2012 |publisher=Smithsonian Media |access-date=August 24, 2013 |journal=Smithsonian Magazine |volume=25 |page=469 |doi=10.1671/0272-4634(2005)025[0469:TRFTUC]2.0.CO;2 |s2cid=131583311 |archive-date=April 12, 2019 |archive-url=https://web.archive.org/web/20190412174912/https://www.smithsonianmag.com/science-nature/when-tyrannosaurus-chomped-sauropods-67170161/ |url-status=live }}</ref> Enamel δ<sup>44/42</sup>Ca values also suggest the possibility that ''T. rex'' occasionally fed on carcasses of marine reptiles and fish washed up on the shores of the Western Interior Seaway.<ref>{{Cite journal |last1=Martin |first1=Jeremy E. |last2=Hassler |first2=Auguste |last3=Montagnac |first3=Gilles |last4=Therrien |first4=François |last5=Balter |first5=Vincent |date=February 10, 2022 |title=The stability of dinosaur communities before the Cretaceous–Paleogene (K–Pg) boundary: A perspective from southern Alberta using calcium isotopes as a dietary proxy |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article/134/9-10/2548/611716/The-stability-of-dinosaur-communities-before-the |journal=[[Geological Society of America Bulletin]] |language=en |volume=134 |issue=9–10 |pages=2548–2560 |doi=10.1130/B36222.1 |bibcode=2022GSAB..134.2548M |issn=0016-7606 |access-date=November 18, 2024 |via=GeoScienceWorld|hdl=2164/20498 |hdl-access=free }}</ref> A study in 2012 by Karl Bates and Peter Falkingham found that ''Tyrannosaurus'' had the most powerful bite of any terrestrial animal that has ever lived, finding an adult ''Tyrannosaurus'' could have exerted 35,000 to 57,000 [[Newton (unit)|N]] (7,868 to 12,814 [[Pound (force)|lbf]]) of force in the back teeth.<ref>{{Cite web |url=https://www.smithsonianmag.com/science-nature/the-tyrannosaurus-rexs-dangerous-and-deadly-bite-37252918/ |title=The ''Tyrannosaurus rex''s Dangerous and Deadly Bite |last=Black |first=Riley |date=2012 |website=Smithsonian Magazine |publisher=Smithsonian Institution |access-date=December 20, 2019 |archive-date=May 13, 2014 |archive-url=https://web.archive.org/web/20140513065820/https://www.smithsonianmag.com/science-nature/the-tyrannosaurus-rexs-dangerous-and-deadly-bite-37252918/ |url-status=live }}</ref><ref name="BatesFalkingham2012">{{Cite journal |last1=Bates |first1=K. T. |last2=Falkingham |first2=P. L. |date=February 29, 2012 |title=Estimating maximum bite performance in ''Tyrannosaurus rex'' using multi-body dynamics |journal=Biology Letters |volume=8 |issue=4 |pages=660–664 |doi=10.1098/rsbl.2012.0056 |pmc=3391458 |pmid=22378742 }}</ref><ref>{{Cite book |title=Oxford Handbook of Applied Dental Sciences |last=Scully |first=C. |publisher=Oxford University Press |year=2002 |isbn=978-0-19-851096-3 |page=[https://archive.org/details/oxfordhandbookof00cris/page/156 156] |url=https://archive.org/details/oxfordhandbookof00cris |url-access=registration }}</ref> Even higher estimates were made by Mason B. Meers in 2003.<ref name="MM03" /> This allowed it to crush bones during repetitive biting and fully consume the carcasses of large dinosaurs.<ref name="gignac" /> Stephan Lautenschlager and colleagues calculated that ''Tyrannosaurus'' was capable of a maximum jaw gape of around 80 degrees, a necessary adaptation for a wide range of jaw angles to power the creature's strong bite.<ref>{{Cite journal |title=Estimating cranial musculoskeletal constraints in theropod dinosaurs |date=November 4, 2015 |journal=Royal Society Open Science |volume=2 |issue=11 |page=150495 |doi=10.1098/rsos.150495 |pmid=26716007 |pmc=4680622 |last1=Lautenschlager |first1=Stephan |bibcode=2015RSOS....250495L }}</ref><ref>{{Cite web |url=https://www.sciencedaily.com/releases/2015/11/151103213705.htm |title=The better to eat you with? How dinosaurs' jaws influenced diet |date=November 3, 2015 |website=Science Daily |archive-url=https://web.archive.org/web/20151104162130/https://www.sciencedaily.com/releases/2015/11/151103213705.htm |archive-date=November 4, 2015 |access-date=September 14, 2018}}</ref>

A debate exists, however, about whether ''Tyrannosaurus'' was primarily a [[predation|predator]] or a pure [[scavenger]]. The debate originated in a 1917 study by Lambe which argued that large theropods were pure scavengers because ''Gorgosaurus'' teeth showed hardly any wear.<ref name="Lambe1917Gorgosaurus">{{Cite journal |last=Lambe |first=L. B. |year=1917 |title=The Cretaceous theropodous dinosaur ''Gorgosaurus'' |journal=Memoirs of the Geological Survey of Canada |volume=100 |pages=1–84 |doi=10.4095/101672 |url=https://www.biodiversitylibrary.org/item/252624 |doi-access=free |archive-date=September 9, 2021 |access-date=August 11, 2021 |archive-url=https://web.archive.org/web/20210909121735/https://www.biodiversitylibrary.org/item/252624 |url-status=live }}</ref> This argument disregarded the fact that theropods replaced their teeth quite rapidly. Ever since the first discovery of ''Tyrannosaurus'' most scientists have speculated that it was a predator; like modern large predators it would readily scavenge or steal another predator's kill if it had the opportunity.<ref name="FarlowHoltz2002FossilRecordPredation">{{Cite book |title=The Fossil Record of Predation |last1=Farlow |first1=J. O. |last2=Holtz |publisher=T. R. Jr. |year=2002 |editor-last=Kowalewski |editor-first=M. |series=The Paleontological Society Papers |volume=8 |pages=251–266 |chapter=The fossil record of predation in dinosaurs |editor-last2=Kelley |editor-first2=P. H. |chapter-url=http://www.yale.edu/ypmip/predation/Chapter_09.pdf |archive-url=https://web.archive.org/web/20081031093048/http://www.yale.edu/ypmip/predation/Chapter_09.pdf |archive-date=October 31, 2008 }}</ref>

Paleontologist [[Jack Horner (paleontologist)|Jack Horner]] has been a major proponent of the view that ''Tyrannosaurus'' was not a predator at all but instead was exclusively a scavenger.<ref name="hornerlessem1993" /><ref name="Horner1994SteakKnives">{{Cite journal |last=Horner |first=J. R. |year=1994 |title=Steak knives, beady eyes, and tiny little arms (a portrait of ''Tyrannosaurus'' as a scavenger) |journal=The Paleontological Society Special Publication |volume=7 |pages=157–164|doi=10.1017/S2475262200009497 }}</ref><ref name="BBC2003TrexOnTrial">{{cite news |url=http://news.bbc.co.uk/1/hi/sci/tech/3112527.stm |title=Science/Nature: ''T. rex'' goes on trial |last=Amos |first=J. |date=July 31, 2003 |work=BBC News |access-date=December 23, 2015 |archive-date=March 13, 2012 |archive-url=https://web.archive.org/web/20120313130020/http://news.bbc.co.uk/1/hi/sci/tech/3112527.stm |url-status=live }}</ref> He has put forward arguments in the popular literature to support the pure scavenger hypothesis:

* Tyrannosaur arms are short when compared to other known predators. Horner argues that the arms were too short to make the necessary gripping force to hold on to prey.<ref name="BBC2003TrexOnTrial2">{{cite news|last=Amos|first=J.|date=July 31, 2003|title=Science/Nature: ''T. rex'' goes on trial|work=BBC News|url=http://news.bbc.co.uk/1/hi/sci/tech/3112527.stm|access-date=December 23, 2015|archive-date=March 13, 2012|archive-url=https://web.archive.org/web/20120313130020/http://news.bbc.co.uk/1/hi/sci/tech/3112527.stm|url-status=live}}</ref> Other paleontologists such as [[Thomas R. Holtz Jr.|Thomas Holtz Jr.]] argued that there are plenty of modern-day predators that do not use their forelimbs to hunt such as [[Wolf|wolves]], [[hyena]]s, and [[Secretarybird|secretary birds]] as well as other extinct animals thought to be predators that would not have used their forelimbs such as [[Phorusrhacidae|phorusrhacids]].<ref name="FarlowHoltz2002FossilRecordPredation2">{{Cite journal|last1=Farlow|first1=J. O.|last2=Holtz|first2=T.R.|year=2002|editor-last=Kowalewski|editor-first=M.|editor2-last=Kelley|editor2-first=P. H.|title=The Fossil Record of Predation in Dinosaurs|url=http://www.yale.edu/ypmip/predation/Chapter_09.pdf|journal=The Paleontological Society Papers|volume=8|pages=251–266|doi=10.1017/S108933260000111X|archive-url=https://web.archive.org/web/20081031093048/http://www.yale.edu/ypmip/predation/Chapter_09.pdf|archive-date=October 31, 2008}}</ref><ref name="Tyrantkingbook">{{cite book|last1=Holtz|first1=Thomas R.|title=Tyrannosaurus rex: The Tyrant King|publisher=Book Publishers|year=2008|isbn=978-0-253-35087-9|editor-last1=Larson|editor-first1=Peter|pages=371–394|chapter=Chapter 20: A critical re-appraisal of the obligate scavenging hypothesis for Tyrannosaurus rex and other tyrant dinosaurs|editor-last2=Carpenter|editor-first2=Kenneth|chapter-url=https://www.academia.edu/293223|archive-date=November 15, 2021|access-date=November 15, 2021|archive-url=https://web.archive.org/web/20211115021956/https://www.academia.edu/293223|url-status=live}}</ref>
* Tyrannosaurs had large [[olfactory bulb]]s and [[olfactory nerve]]s (relative to their brain size). These suggest a highly developed sense of smell which could sniff out carcasses over great distances, as modern [[vulture]]s do. Research on the olfactory bulbs of dinosaurs has shown that ''Tyrannosaurus'' had the most highly developed sense of smell of 21 sampled dinosaurs.<ref name="Calgary Herald" />
* Tyrannosaur teeth could crush bone, and therefore could extract as much food ([[bone marrow]]) as possible from carcass remnants, usually the least nutritious parts. Karen Chin and colleagues have found bone fragments in [[coprolite]]s (fossilized feces) that they attribute to tyrannosaurs, but point out that a tyrannosaur's teeth were not well adapted to systematically chewing bone like [[hyena]]s do to extract marrow.<ref name="ChinEtal1998KingSizeCoprolite">{{Cite journal |last1=Chin |first1=K. |last2=Tokaryk |first2=T. T. |last3=Erickson |first3=G. M. |last4=Calk |first4=L. C. |s2cid=4343329 |date=June 18, 1998 |title=A king-sized theropod coprolite |journal=Nature |volume=393 |issue=6686 |pages=680–682 |bibcode=1998Natur.393..680C |doi=10.1038/31461|url=https://zenodo.org/record/3943146 }} Summary at {{cite journal |last=Monastersky |first=R. |date=June 20, 1998 |title=Getting the scoop from the poop of ''T. rex'' |journal=Science News |doi=10.2307/4010364 |jstor=4010364 |volume=153 |issue=25 |page=391 |url=http://www.sciencenews.org/pages/sn_arc98/6_20_98/fob2.htm |archive-url=https://web.archive.org/web/20130511121022/http://www.sciencenews.org/pages/sn_arc98/6_20_98/fob2.htm |archive-date=May 11, 2013}}</ref>
* Since at least some of ''Tyrannosaurus''{{'}}s potential prey could move quickly, evidence that it walked instead of ran could indicate that it was a scavenger.<ref name="Horner1994SteakKnives" /> On the other hand, recent analyses suggest that ''Tyrannosaurus'', while slower than large modern terrestrial predators, may well have been fast enough to prey on large [[hadrosaurs]] and [[ceratopsians]].<ref name="HutchinsonGarcia2002TrexSlow" /><ref name="manningetal2008" />

Other evidence suggests hunting behavior in ''Tyrannosaurus''. The eye sockets of tyrannosaurs are positioned so that the eyes would point forward, giving them [[binocular vision]] slightly better than that of modern [[hawk]]s. It is not obvious why [[natural selection]] would have favored this long-term trend if tyrannosaurs had been pure scavengers, which would not have needed the advanced [[depth perception]] that [[stereoscopic vision]] provides.<ref name="Stevens2006Binocular" /><ref name="jaffe" /> In modern animals, binocular vision is found mainly in predators.

[[File:DMNS Edmontosaurus.png|thumb|left|The damage to the tail vertebrae of this ''Edmontosaurus annectens'' skeleton (on display at the Denver Museum of Nature and Science) indicates that it may have been bitten by a ''Tyrannosaurus'']]
A skeleton of the hadrosaurid ''[[Edmontosaurus]] annectens'' has been described from Montana with healed tyrannosaur-inflicted damage on its tail [[vertebra]]e. The fact that the damage seems to have healed suggests that the ''Edmontosaurus'' survived a tyrannosaur's attack on a living target, i.e. the tyrannosaur had attempted active predation.<ref name="carpenter1998">{{Cite journal |last=Carpenter |first=K. |author-link=Kenneth Carpenter |year=1998 |title=Evidence of predatory behavior by theropod dinosaurs |url=http://vertpaleo.org/publications/jvp/15-576-591.cfm |journal=Gaia |volume=15 |pages=135–144 |archive-url=https://web.archive.org/web/20071117132451/http://vertpaleo.org/publications/jvp/15-576-591.cfm <!--Added by H3llBot--> |archive-date=November 17, 2007 |access-date=December 5, 2007}}</ref> Despite the consensus that the tail bites were caused by ''Tyrannosaurus'', there has been some evidence to show that they might have been created by other factors. For example, a 2014 study suggested that the tail injuries might have been due to ''Edmontosaurus'' individuals stepping on each other,<ref>{{cite book|title=Hadrosaurs|chapter=Paleopathology in Late Cretaceous Hadrosauridae from Alberta, Canada |date=2015|pages=540–571|publisher=Indiana University Press|isbn=978-0-253-01390-3|editor1=Eberth, David A.|editor2=Evans, David C.}} [https://www.researchgate.net/publication/290310286_Paleopathology_in_Late_Cretaceous_Hadrosauridae_from_Alberta_Canada preprint] {{Webarchive|url=https://web.archive.org/web/20200703105409/https://www.researchgate.net/publication/290310286_Paleopathology_in_Late_Cretaceous_Hadrosauridae_from_Alberta_Canada |date=July 3, 2020 }}</ref> while another study in 2020 backs up the hypothesis that biomechanical stress is the cause for the tail injuries.<ref>{{cite journal |journal=PALAIOS |date=2020 |volume=35 |issue=4 |doi=10.2110/palo.2019.079 |url=https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/35/4/201/584648/SKELETAL-TRAUMA-WITH-IMPLICATIONS-FOR-INTRATAIL?redirectedFrom=fulltext-- |title=Skeletal Trauma with Implications for Intratail Mobility in Edmontosaurus Annectens from a Monodominant Bonebed, Lance Formation (Maastrichtian), Wyoming USA |last1=Siviero |first1=ART V. |last2=Brand |first2=Leonard R. |last3=Cooper |first3=Allen M. |last4=Hayes |first4=William K. |last5=Rega |first5=Elizabeth |last6=Siviero |first6=Bethania C.T. |s2cid=218503493 |pages=201–214 |bibcode=2020Palai..35..201S |archive-date=July 4, 2020 |access-date=July 2, 2020 |archive-url=https://web.archive.org/web/20200704084853/https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/35/4/201/584648/SKELETAL-TRAUMA-WITH-IMPLICATIONS-FOR-INTRATAIL?redirectedFrom=fulltext-- |url-status=live }}</ref> There is also evidence for an aggressive interaction between a ''[[Triceratops]]'' and a ''Tyrannosaurus'' in the form of partially healed tyrannosaur tooth marks on a ''Triceratops'' brow horn and [[squamosal]] (a bone of the [[neck frill]]); the bitten horn is also broken, with new bone growth after the break. It is not known what the exact nature of the interaction was, though: either animal could have been the aggressor.<ref name="JH08">{{Cite book |title=Tyrannosaurus rex, the Tyrant King (Life of the Past) |last1=Happ |first1=J. |last2=Carpenter |first2=K. |publisher=Indiana University Press |year=2008 |isbn=978-0-253-35087-9 |editor-last=Carpenter |editor-first=K. |location=Bloomington |pages=355–368 |chapter=An analysis of predator–prey behavior in a head-to-head encounter between ''Tyrannosaurus rex'' and ''Triceratops'' |editor-last2=Larson |editor-first2=P. E.}}</ref> Since the ''Triceratops'' wounds healed, it is most likely that the ''Triceratops'' survived the encounter and managed to overcome the ''Tyrannosaurus''. In a battle against a bull ''Triceratops'', the ''Triceratops'' would likely defend itself by inflicting fatal wounds to the ''Tyrannosaurus'' using its sharp horns.<ref>{{Cite book |title=The Horned Dinosaurs |year=1996 |url=https://archive.org/details/horneddinosaursn00dods |url-access=limited |last=Dodson |first=P. |publisher=Princeton University Press |page=[https://archive.org/details/horneddinosaursn00dods/page/n32 19]}}</ref> Studies of [[Sue (dinosaur)|Sue]] found a broken and healed [[fibula]] and tail vertebrae, scarred facial bones and a tooth from another ''Tyrannosaurus'' embedded in a neck vertebra, providing evidence for aggressive behavior.<ref name="TC98">{{Cite journal |last1=Tanke |first1=D. H. |last2=Currie |first2=P. J. |year=1998 |title=Head-biting behavior in theropod dinosaurs: paleopathological evidence |url=http://www.mnhn.ul.pt/geologia/gaia/12.pdf  |journal=Gaia |issue=15 |pages=167–184 |issn=0871-5424 |archive-url=https://web.archive.org/web/20080227134632/http://www.mnhn.ul.pt/geologia/gaia/12.pdf |archive-date=February 27, 2008 |author-link=Darren Tanke}}</ref> Studies on hadrosaur vertebrae from the Hell Creek Formation that were punctured by the teeth of what appears to be a late-stage juvenile ''Tyrannosaurus'' indicate that despite lacking the bone-crushing adaptations of the adults, young individuals were still capable of using the same bone-puncturing feeding technique as their adult counterparts.<ref name="Peterson">{{Cite journal |last1=Peterson |first1=J. E. |last2=Daus |first2=K. N. |date=March 4, 2019 |title=Feeding traces attributable to juvenile ''Tyrannosaurus rex'' offer insight into ontogenetic dietary trends |journal=PeerJ |volume=7 |page=e6573 |doi=10.7717/peerj.6573 |issn=2167-8359 |pmid=30863686|pmc=6404657 |doi-access=free }}</ref>

''Tyrannosaurus'' may have had infectious [[saliva]] used to kill its prey, as proposed by [[William Abler]] in 1992. Abler observed that the {{Dinogloss|serrations}} (tiny protuberances) on the cutting edges of the teeth are closely spaced, enclosing little chambers. These chambers might have trapped pieces of carcass with bacteria, giving ''Tyrannosaurus'' a deadly, infectious bite much like the [[Komodo dragon]] was thought to have.<ref name="abler1992">{{Cite journal |last=Abler |first=W. L. |date=1992 |title=The serrated teeth of tyrannosaurid dinosaurs, and biting structures in other animals |journal=Paleobiology |volume=18 |issue=2 |pages=161–183 |doi=10.1017/S0094837300013956|bibcode=1992Pbio...18..161A |s2cid=88238481 }}</ref><ref name="goldstein2013">{{Cite journal |last1=Goldstein |first1=E. J. C. |last2=Tyrrell |first2=K. L. |last3=Citron |first3=D. M. |last4=Cox |first4=C. R. |last5=Recchio |first5=I. M. |last6=Okimoto |first6=B. |last7=Bryja |first7=J. |last8=Fry |first8=B. G. |s2cid=9932073 |date=June 1, 2013 |title=Anaerobic and aerobic bacteriology of the saliva and gingiva from 16 captive Komodo dragons (''Varanus komodoensis''): new implications for the "bacteria as venom" model |journal=Journal of Zoo and Wildlife Medicine |volume=44 |issue=2 |pages=262–272 |doi=10.1638/2012-0022R.1 |pmid=23805543 |issn=1042-7260}}</ref> Jack Horner and Don Lessem, in a 1993 popular book, questioned Abler's hypothesis, arguing that ''Tyrannosaurus''{{'}}s tooth serrations as more like cubes in shape than the serrations on a Komodo monitor's teeth, which are rounded.<ref name="hornerlessem1993" />{{rp|214–215}}

''Tyrannosaurus'', and most other theropods, probably primarily processed carcasses with lateral shakes of the head, like crocodilians. The head was not as maneuverable as the skulls of [[allosauroidea|allosauroids]], due to flat joints of the neck vertebrae.<ref name="ESetal2013">{{Cite journal |last1=Snively |first1=E. |last2=Cotton |first2=J. R. |last3=Ridgely |first3=R. |last4=Witmer |first4=L. M. |year=2013 |title=Multibody dynamics model of head and neck function in ''Allosaurus'' (Dinosauria, Theropoda) |journal=Palaeontologia Electronica |volume=16 |issue=2 |doi=10.26879/338|doi-access=free |bibcode=2013PalEl..16..338S }}</ref>

====Cannibalism====
Evidence also strongly suggests that tyrannosaurs were at least occasionally cannibalistic. ''Tyrannosaurus'' itself has strong evidence pointing towards it having been cannibalistic in at least a scavenging capacity based on tooth marks on the foot bones, humerus, and metatarsals of one specimen.<ref name="HornerCurrie_et.al._2010_Trex_cannibalism">{{Cite journal |last1=Longrich |first1=N. R. |last2=Horner |first2=J. R. |last3=Erickson |first3=G. M. |last4=Currie |first4=P. J. |year=2010 |title=Cannibalism in ''Tyrannosaurus rex'' |journal=PLOS ONE |volume=5 |issue=10 |page=e13419 |doi=10.1371/journal.pone.0013419 |pmc=2955550 |pmid=20976177|bibcode=2010PLoSO...513419L |doi-access=free }}</ref> Fossils from the [[Fruitland Formation]], [[Kirtland Formation]] (both Campanian in age) and the Maastrichtian aged [[Ojo Alamo Formation]] suggest that cannibalism was present in various tyrannosaurid genera of the San Juan Basin. The evidence gathered from the specimens suggests opportunistic feeding behavior in tyrannosaurids that cannibalized members of their own species.<ref>{{Cite web|url=https://www.researchgate.net/publication/348002335|title=NEW EVIDENCE FOR CANNIBALISM IN TYRANNOSAURID DINOSAURS FROM THE UPPER CRETACEOUS (CAMPANIAN/MAASTRICHTIAN) SAN JUAN BASIN OF NEW MEXICO|website=ResearchGate|access-date=May 8, 2021|archive-date=November 10, 2021|archive-url=https://web.archive.org/web/20211110091047/https://www.researchgate.net/publication/348002335_NEW_EVIDENCE_FOR_CANNIBALISM_IN_TYRANNOSAURID_DINOSAURS_FROM_THE_UPPER_CRETACEOUS_CAMPANIANMAASTRICHTIAN_SAN_JUAN_BASIN_OF_NEW_MEXICO|url-status=live}}</ref> A study from Currie, Horner, Erickson and Longrich in 2010 has been put forward as evidence of cannibalism in the genus ''Tyrannosaurus''.<ref name=HornerCurrie_et.al._2010_Trex_cannibalism/> They studied some ''Tyrannosaurus'' specimens with tooth marks in the bones, attributable to the same genus. The tooth marks were identified in the [[humerus]], foot bones and [[metatarsal]]s, and this was seen as evidence for opportunistic scavenging, rather than wounds caused by intraspecific combat. In a fight, they proposed it would be difficult to reach down to bite in the feet of a rival, making it more likely that the bitemarks were made in a carcass. As the bitemarks were made in body parts with relatively scantly amounts of flesh, it is suggested that the ''Tyrannosaurus'' was feeding on a cadaver in which the more fleshy parts already had been consumed. They were also open to the possibility that other [[Tyrannosauridae|tyrannosaurids]] practiced cannibalism.<ref name=HornerCurrie_et.al._2010_Trex_cannibalism />

=== Parenting ===
While there is no direct evidence of ''Tyrannosaurus'' raising their young (the rarity of juvenile and nest Tyrannosaur fossils has left researchers guessing), it has been suggested by some that like its closest living relatives, modern archosaurs (birds and crocodiles) ''Tyrannosaurus'' may have protected and fed its young. Crocodilians and birds are often suggested by some paleontologists to be modern analogues for dinosaur parenting.<ref>{{Cite book|last=Farlow|first=James Orville|url=https://books.google.com/books?id=jXU6atz3RTYC&dq=dinosaur+parenting+behavior&pg=PA21|title=Paleobiology of the Dinosaurs|date=1989|publisher=Geological Society of America|isbn=978-0-8137-2238-2|language=en}}</ref> Direct evidence of parental behavior exists in other dinosaurs such as ''[[Maiasaura|Maiasaura peeblesorum]]'', the first dinosaur to have been discovered to raise its young, as well as more closely related [[Oviraptoridae|Oviraptorids]], the latter suggesting parental behavior in theropods.<ref>"Maiasaura," Dodson, et al. (1994); pages 116-117</ref><ref>{{cite journal|last1=Horner|first1=J.R.|last2=Makela|first2=R.|year=1979|title=Nest of juveniles provides evidence of family structure among dinosaurs|journal=Nature|volume=282|issue=5736|pages=296–298|bibcode=1979Natur.282..296H|doi=10.1038/282296a0|s2cid=4370793}}</ref><ref>{{cite web|title="The Best of all Mothers" Maiasaura peeblesorum|url=http://bioweb.uwlax.edu/bio203/s2014/fischbac_sama/interactions.htm|access-date=March 22, 2021|website=bioweb.uwlax.edu/|publisher=University of Wisconsin-La Crosse|archive-date=June 16, 2022|archive-url=https://web.archive.org/web/20220616015020/http://bioweb.uwlax.edu/bio203/s2014/fischbac_sama/interactions.htm|url-status=live}}</ref><ref>{{Cite journal|last1=Norell|first1=Mark A.|last2=Clark|first2=James M.|last3=Chiappe|first3=Luis M.|last4=Dashzeveg|first4=Demberelyin|date=1995|title=A nesting dinosaur|url=https://www.nature.com/articles/378774a0|journal=Nature|language=en|volume=378|issue=6559|pages=774–776|doi=10.1038/378774a0|bibcode=1995Natur.378..774N|s2cid=4245228|issn=1476-4687}}</ref><ref>{{Cite journal|last=Watanabe|first=Myrna E.|date=March 1, 2009|title=Evolving Ideas on the Origins of Parental Care|journal=BioScience|volume=59|issue=3|page=272|doi=10.1525/bio.2009.59.3.17|s2cid=85066992|issn=0006-3568}}</ref>

===Pathology===
[[File:T. rex infection.png|thumb|Restoration of an individual (based on [[MOR 980]]) with parasite infections]]
In 2001, Bruce Rothschild and others published a study examining evidence for [[stress fractures]] and [[tendon avulsions]] in [[theropod]] dinosaurs and the implications for their behavior. Since stress fractures are caused by repeated trauma rather than singular events they are more likely to be caused by regular behavior than other types of injuries. Of the 81 ''Tyrannosaurus'' foot bones examined in the study, one was found to have a stress fracture, while none of the 10 hand bones were found to have stress fractures. The researchers found tendon avulsions only among ''Tyrannosaurus'' and ''[[Allosaurus]]''. An avulsion injury left a divot on the humerus of Sue the ''T.&nbsp;rex'', apparently located at the origin of the [[deltoid muscle|deltoid]] or [[teres major]] muscles. The presence of avulsion injuries being limited to the forelimb and shoulder in both ''Tyrannosaurus'' and ''Allosaurus'' suggests that theropods may have had a musculature more complex than and functionally different from those of birds. The researchers concluded that Sue's tendon avulsion was probably obtained from struggling prey. The presence of stress fractures and tendon avulsions, in general, provides evidence for a "very active" predation-based diet rather than obligate scavenging.<ref name="rothschild-dino">{{Cite book |title=Mesozoic Vertebrate Life |last1=Rothschild |first1=B. |last2=Tanke |first2=D. H. |last3=Ford |first3=T. L. |publisher=Indiana University Press |year=2001 |editor-last=Tanke |editor-first=D. H. |pages=331–336 |chapter=Theropod stress fractures and tendon avulsions as a clue to activity |editor-last2=Carpenter |editor-first2=K.}}</ref>

A 2009 study showed that smooth-edged holes in the skulls of several specimens might have been caused by ''[[Trichomonas]]''-like parasites that commonly infect [[bird]]s. According to the study, seriously infected individuals, including "Sue" and MOR 980 ("Peck's Rex"), might therefore have died from starvation after feeding became increasingly difficult. Previously, these holes had been explained by the bacterious bone infection [[Actinomycosis]] or by intraspecific attacks.<ref name="Wolff">{{Cite journal |last1=Wolff |first1=E. D. S. |last2=Salisbury |first2=S. W. |last3=Horner |first3=J. R. |last4=Varricchi |first4=D. J. |year=2009 |editor-last=Hansen |editor-first=D. M. |title=Common Avian Infection Plagued the Tyrant Dinosaurs |journal=PLOS ONE |volume=4 |issue=9 |page=e7288 |bibcode=2009PLoSO...4.7288W |doi=10.1371/journal.pone.0007288 |pmc=2748709 |pmid=19789646|doi-access=free }}</ref> A subsequent study found that while trichomoniasis has many attributes of the model proposed (osteolytic, intra oral) several features make the assumption that it was the cause of death less supportable by evidence. For example, the observed sharp margins with little reactive bone shown by the radiographs of ''Trichomonas''-infected birds are dissimilar to the reactive bone seen in the affected ''T. rex'' specimens. Also, trichomoniasis can be very rapidly fatal in birds (14 days or less) albeit in its milder form, and this suggests that if a ''Trichomonas''-like protozoan is the culprit, trichomoniasis was less acute in its non-avian dinosaur form during the Late Cretaceous. Finally, the relative size of this type of lesions is much larger in small bird throats, and may not have been enough to choke a ''T. rex''.<ref>{{Cite book |last=Rega |first=E. |chapter=Disease in Dinosaurs |editor-last1=Brett-Surman |editor-first1=M. |editor-last2=Holtz |editor-first2=T. |editor-last3=Farlow |editor-first3=J. |title=The Complete Dinosaur |publisher=Indiana University Press |location=Bloomington |year=2012}}</ref> A more recent study examining the pathologies concluded that the osseous alteration observed most closely resembles those around healing human cranial trepanations and healing fractures in the Triassic reptile ''[[Stagonolepis]],'' in the absence of infection. The possible cause may instead have been intraspecific combat.<ref>{{Cite journal |last1=Rothschild |first1=Bruce |last2=O'Connor |first2=Jingmai |last3=Lozado |first3=María Cecilia |date=December 1, 2022 |title=Closer examination does not support infection as cause for enigmatic Tyrannosaurus rex mandibular pathologies |url=https://www.sciencedirect.com/science/article/pii/S0195667122002178 |journal=Cretaceous Research |language=en |volume=140 |page=105353 |doi=10.1016/j.cretres.2022.105353 |bibcode=2022CrRes.14005353R |s2cid=252055157 |issn=0195-6671}}</ref>

One study of ''Tyrannosaurus'' specimens with tooth marks in the bones attributable to the same genus was presented as evidence of [[cannibalism]].<ref name="HornerCurrie_et.al._2010_Trex_cannibalism"/> Tooth marks in the [[humerus]], foot bones and [[metatarsal]]s, may indicate opportunistic scavenging, rather than wounds caused by combat with another ''T. rex''.<ref name="HornerCurrie_et.al._2010_Trex_cannibalism" /><ref>{{Cite journal |last=Perkins |first=S. |date=October 29, 2015 |title=Tyrannosaurs were probably cannibals (Comment) |url=https://www.science.org/content/article/tyrannosaurs-were-probably-cannibals |journal=Science |access-date=November 2, 2015 |archive-date=October 5, 2022 |archive-url=https://web.archive.org/web/20221005112604/https://www.science.org/content/article/tyrannosaurs-were-probably-cannibals |url-status=live }}</ref> Other [[tyrannosaurids]] may also have practiced cannibalism.<ref name="HornerCurrie_et.al._2010_Trex_cannibalism" />