Editing Gorgosaurus

{{Short description|Genus of tyrannosaur dinosaur}}
{{For|the fictional monster|Gorosaurus}}
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{{Use mdy dates|date=May 2024}}
{{Automatic taxobox
| fossil_range = [[Late Cretaceous]] ([[Campanian]]), ~{{fossil range|76.5|75}}
| image = Drumheller 150.jpg
| image_upright = 1.15
| image_caption = Skeletal mount, [[Royal Tyrrell Museum of Palaeontology]]
| display_parents = 3
| taxon = Gorgosaurus 
| authority = [[Lawrence Lambe|Lambe]], 1914
| type_species = {{extinct}}'''''Gorgosaurus libratus'''''
| type_species_authority = Lambe, 1914
| synonyms = {{collapsible list|bullets = true|title=<small>List</small>
|''Deinodon horridus''? <br/><small>[[Joseph Leidy|Leidy]], 1856</small>
|''Laelaps falculus''? <br/><small>[[Edward Drinker Cope|Cope]], 1876</small>
|''Laelaps hazenianus''? <br/><small>Cope, 1876</small>
|''Laelaps incrassatus'' <br/><small>Cope, 1876</small>
|''Dryptosaurus kenabekides''? <br/><small>Hay, 1899</small>
|''Gorgosaurus sternbergi'' <br/><small>[[William Diller Matthew|Matthew]] & [[Barnum Brown|Brown]], 1923</small>
|''[[Albertosaurus]] libratus'' <br/><small>(Lambe, 1914)</small>
}} 
}}

'''''Gorgosaurus''''' ({{IPAc-en|ˌ|ɡ|ɔːr|ɡ|ə|ˈ|s|ɔːr|ə|s}} {{respell|GOR|gə|SOR|əs}}; {{lit|dreadful lizard}}) is a [[genus]] of [[tyrannosaurid]] [[theropod]] [[dinosaur]] that lived in western North America during the [[Late Cretaceous]] [[Period (geology)|Period]] ([[Campanian]]), between about 76.5 and 75&nbsp;[[million years ago]].<ref>{{cite journal|last1=Gardner|first1=James D.|last2=Henderson|first2=Donald M.|last3=Therrien|first3=François|title=Introduction to the Special Issue commemorating the 30th anniversary of the Royal Tyrrell Museum of Palaeontology, with a summary of the museum's early history and its research contributions|journal=Canadian Journal of Earth Sciences|year=2015|volume=52|issue=8|page=7|doi=10.1139/cjes-2015-0059|bibcode=2015CaJES..52D...5G|doi-access=free}}</ref> [[Fossil]] remains have been found in the [[Provinces and territories of Canada|Canadian province]] of [[Alberta]] and the [[U.S. state]] of [[Montana]]. [[Paleontologist]]s recognize only the [[type species]], ''G. libratus'', although other species have been erroneously referred to the genus.

Like most known tyrannosaurids, ''Gorgosaurus'' was a large [[biped]]al [[predation|predator]], measuring {{convert|8|-|9|m|ft}} in length and {{convert|2|-|3|MT|ST}} in body mass. Dozens of large, sharp teeth lined its jaws, while its two-fingered forelimbs were comparatively small. ''Gorgosaurus'' was most closely related to ''[[Albertosaurus]]'', and more distantly related to the larger ''[[Tyrannosaurus]]''. ''Gorgosaurus'' and ''Albertosaurus'' are extremely similar, distinguished mainly by subtle differences in the teeth and skull bones. Some experts consider ''G. libratus'' to be a species of ''Albertosaurus''; this would make ''Gorgosaurus'' a [[junior synonym]] of that genus.

''Gorgosaurus'' lived in a lush [[floodplain]] environment along the edge of an [[Western Interior Seaway|inland sea]]. It was an [[apex predator]], preying upon abundant [[ceratopsid]]s and [[hadrosaur]]s. In some areas, ''Gorgosaurus'' coexisted with another tyrannosaurid, ''[[Daspletosaurus]]''. Although these animals were roughly the same size, there is some evidence of [[niche differentiation]] between the two. ''Gorgosaurus'' is the best-represented tyrannosaurid in the fossil record, known from dozens of specimens. These plentiful remains have allowed scientists to investigate its [[ontogeny]], [[Biological life cycle|life history]] and other aspects of its [[biology]].

== Discovery and naming ==
[[File:Sharp naturalhistory1920 deinodon.jpg|thumb|left|[[Type specimen]] of ''Gorgosaurus sternbergi'' ([[American Museum of Natural History|AMNH]] 5664), now recognized as a juvenile ''Gorgosaurus libratus'']]
''Gorgosaurus libratus'' was first described by [[Lawrence Lambe]] in 1914.<ref name=lambe1914a>{{cite journal |last=Lambe |first=Lawrence M. |author-link=Lawrence Lambe |year=1914 |title=On the fore-limb of a carnivorous dinosaur from the Belly River Formation of Alberta, and a new genus of Ceratopsia from the same horizon, with remarks on the integument of some Cretaceous herbivorous dinosaurs |journal=Ottawa Naturalist |volume=27 |pages=129–135}}</ref><ref name=lambe1914b>{{cite journal |last=Lambe |first=Lawrence 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 ''Stephanosaurus marginatus'' from the same horizon |journal=Ottawa Naturalist |volume=28 |pages=13–20 |url=https://www.biodiversitylibrary.org/page/5739477#page/19/mode/1up}}</ref> Its name is derived from the [[Ancient Greek|Greek]] {{lang|grc|{{math|γοργος}}}} (''gorgos'' – "fierce" or "terrible") and {{lang|grc|{{math|σαυρος}}}} (''saurus'' – "lizard").<ref name=liddellscott>{{cite book |author1=Liddell, Henry G. |author-link=Henry Liddell |author2=Scott, Robert |author-link2=Robert Scott (philologist) |year=1980 |title=Greek-English Lexicon |edition=abridged |publisher=Oxford University Press |location=Oxford, UK |isbn=978-0-19-910207-5 |url=https://archive.org/details/lexicon00lidd }}</ref> The [[type species]] is ''G.&nbsp;libratus''; the specific epithet "balanced" is the [[past participle]] of the [[Latin]] verb ''librare'', meaning "to balance".<ref name=lambe1914b/>

The [[holotype]] of ''Gorgosaurus libratus'' ([[Canadian Museum of Nature|NMC]] 2120) is a nearly complete skeleton associated with a skull, discovered in 1913 by [[Charles M. Sternberg]]. This specimen was the first tyrannosaurid found with a complete hand.<ref name=lambe1914a/> It was found in the [[Dinosaur Park Formation]] of Alberta and is housed in the [[Canadian Museum of Nature]] in [[Ottawa]].<ref name=currie2003a/> Prospectors from the [[American Museum of Natural History]] in [[New York City]] were active along the [[Red Deer River]] in Alberta at the same time, collecting hundreds of spectacular dinosaur specimens, including four complete ''G.&nbsp;libratus'' skulls, three of which were associated with skeletons. Matthew and Brown described four of these specimens in 1923.<ref name=matthewbrown1923/>

[[File:Gorgosaurus.jpg|thumb|Specimen [[American Museum of Natural History|AMNH]]&nbsp;5458]]
Matthew and Brown also described a fifth skeleton ([[American Museum of Natural History|AMNH]]&nbsp;5664), which [[Charles H. Sternberg]] had collected in 1917 and sold to their museum. It was smaller than other ''Gorgosaurus'' specimens, with a lower, lighter skull and more elongate limb proportions. Many [[Suture (anatomical)|sutures]] between bones were unfused in this specimen as well. Matthew and Brown noted that these features were characteristic of juvenile tyrannosaurids, but still described it as the holotype of a new species, ''G.&nbsp;sternbergi''.<ref name=matthewbrown1923/> Today's paleontologists regard this specimen as a juvenile ''G.&nbsp;libratus''.<ref name=holtz2004/><ref name=currie2003a/> Dozens of other specimens have been excavated from the Dinosaur Park Formation and are housed in museums across the United States and Canada.<ref name=russell1970/><ref name=currie2003a/> ''G.&nbsp;libratus'' is the best-represented tyrannosaurid in the fossil record, known from a virtually complete growth series.<ref name=holtz2004/><ref name=carr1999>{{cite journal |doi=10.1080/02724634.1999.10011161 |last=Carr |first=Thomas D. |author-link=Thomas Carr (paleontologist) |year=1999 |title=Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria) |journal=Journal of Vertebrate Paleontology |volume=19 |issue=3 |pages=497–520 |bibcode=1999JVPal..19..497C |s2cid=83744433 |url=http://www.vertpaleo.org/publications/jvp/19-497-520.cfm |access-date=February 27, 2008 |archive-date=September 30, 2008 |archive-url=https://web.archive.org/web/20080930215300/http://www.vertpaleo.org/publications/jvp/19-497-520.cfm |url-status=dead |url-access=subscription }}</ref>

[[File:Gorgosaurus skeleton AMNH 5428.jpg|thumb|left|Specimen [[National Museum of Natural History|USNM]]&nbsp;12814 (formerly [[American Museum of Natural History|AMNH]]&nbsp;5428)]]
In 1856, [[Joseph Leidy]] described two tyrannosaurid premaxillary teeth from Montana. Although there was no indication of what the animal looked like, the teeth were large and robust, and Leidy gave them the name ''[[Deinodon]]''.<ref name=leidy1856>{{cite journal |last=Leidy |first=Joseph |author-link=Joseph Leidy |year=1856 |title=Notice of remains of extinct reptiles and fishes, discovered by Dr. F.V. Hayden in the badlands of the Judith River |journal=Proceedings of the Academy of Sciences in Philadelphia |volume=8 |pages=72–73}}</ref> Matthew and Brown commented in 1922 that these teeth were indistinguishable from those of ''Gorgosaurus'', but in the absence of skeletal remains of ''Deinodon'', opted not to unequivocally synonymize the two genera, provisionally naming a ''?Deinodon libratus''.<ref name=matthewbrown1922/> Although ''Deinodon'' teeth are very similar to those of ''Gorgosaurus'', tyrannosaurid teeth are extremely uniform, so it cannot be said for certain which animal they belonged to. ''Deinodon'' is usually regarded as a ''[[nomen dubium]]'' today.<ref name=carr1999/> Additional likely synonyms of ''G.&nbsp;libratus'' and/or ''D.&nbsp;horridus'' include ''[[Laelaps falculus]]'', ''[[Laelaps hazenianus]]'', ''Laelaps incrassatus'', and ''[[Dryptosaurus kenabekides]]''.<ref name=dinosauria2>{{cite book |editor1=Weishampel, D.B. |editor2=Dodson, P. |editor3=Osmólska, H. |year=2004 |title=The Dinosauria |edition=2nd |publisher=University of California Press |place=Berkeley, CA}}</ref>

Several tyrannosaurid skeletons from the [[Two Medicine Formation]] and [[Judith River Formation]] of [[Montana]] probably belong to ''Gorgosaurus'', although it remains uncertain whether they belong to ''G.&nbsp;libratus'' or a new species.<ref name=currie2003a/> One specimen from Montana ([[Children's Museum of Indianapolis|TCMI]] 2001.89.1), housed in the [[Children's Museum of Indianapolis]], shows evidence of severe [[pathology|pathologies]], including healed leg, rib, and vertebral [[Bone fracture|fractures]], [[osteomyelitis]] (infection) at the tip of the lower jaw resulting in permanent tooth loss, and possibly a [[brain tumor]].<ref name=natlgeo2003>{{Cite web |author=Pickrell, John |date=November 24, 2003 |url=http://news.nationalgeographic.com/news/2003/11/1124_031124_dinocancer.html |archive-url=https://web.archive.org/web/20031126034023/http://news.nationalgeographic.com/news/2003/11/1124_031124_dinocancer.html |url-status=dead |archive-date=November 26, 2003 |title=First dinosaur brain tumor found, experts suggest |publisher=National Geographic News |access-date=February 7, 2008}}</ref><ref name=tcmigorgo>{{Cite web |url=http://www.childrensmuseum.org/themuseum/dinosphere/profiles/gorgo.html |title=Meet the Gorgosaur |publisher=The Children's Museum of Indianapolis |access-date=February 7, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080130171049/http://www.childrensmuseum.org/themuseum/dinosphere/profiles/gorgo.html |archive-date=January 30, 2008 }}</ref>

=== Formerly assigned species ===
[[File:TarbosaurusP1050352.jpg|thumb|Cast of specimen PIN 553–1, holotype of now invalid ''Gorgosaurus lancinator'']]
Several species were incorrectly assigned to ''Gorgosaurus'' in the 20th century. A complete skull of a small tyrannosaurid ([[Cleveland Museum of Natural History|CMNH]] 7541), found in the younger, late [[Maastrichtian]]-age [[Hell Creek Formation]] of Montana, was named ''Gorgosaurus lancensis'' by [[Charles Whitney Gilmore]] in 1946.<ref name=gilmore1946>{{cite journal |last=Gilmore |first=Charles W. |author-link=Charles Whitney Gilmore |year=1946 |title=A new carnivorous dinosaur from the Lance Formation of Montana |journal=Smithsonian Miscellaneous Collections |volume=106 |pages=1–19}}</ref> This specimen was renamed ''[[Nanotyrannus]]'' by [[Robert T. Bakker|Bob Bakker]] and colleagues in 1988.<ref name=bakkeretal1988>{{cite journal |last=Bakker |first=Robert T. |author-link=Robert T. Bakker |author2=Williams, Michael |author3=Currie, Philip J. |author3-link=Phil Currie |year=1988 |title=''Nanotyrannus'', a new genus of pygmy tyrannosaur, from the latest Cretaceous of Montana |journal=Hunteria |volume=1 |issue=5 |pages=1–30}}</ref> Currently, many paleontologists regard ''Nanotyrannus'' as a juvenile ''Tyrannosaurus rex''.<ref name=holtz2004/><ref name=carr1999/> Similarly, [[Evgeny Maleev]] created the names ''Gorgosaurus lancinator'' and ''Gorgosaurus novojilovi'' for two small tyrannosaurid specimens ([[Paleontological Institute of Russian Academy of Sciences|PIN]] 553-1 and PIN 552–2) from the [[Nemegt Formation]] of [[Mongolia]] in 1955.<ref name=maleev1955b>{{cite journal |last=Maleev |first=Evgeny A. |author-link=Evgeny Maleev |year=1955 |title=New carnivorous dinosaurs from the Upper Cretaceous of Mongolia |journal=[[Doklady Akademii Nauk SSSR]] |volume=104 |issue=5 |pages=779–783 |language=ru}}</ref> [[Kenneth Carpenter]] renamed the smaller specimen ''[[Maleevosaurus]] novojilovi'' in 1992,<ref name=carpenter1992>{{Cite book|last=Carpenter |first=Ken. |author-link=Kenneth Carpenter |year=1992 |chapter=Tyrannosaurids (Dinosauria) of Asia and North America |editor=Mateer, Niall J. |editor2=Chen Peiji|title=Aspects of Nonmarine Cretaceous Geology |location=Beijing |publisher=China Ocean Press |pages=250–268 }}</ref> but both are now considered juveniles of ''[[Tarbosaurus bataar]]''.<ref name=holtz2004/><ref name=carr1999/><ref name=rozhdestvensky1965>{{cite journal |last=Rozhdestvensky |first=Anatoly K. |author-link=Anatoly Konstantinovich Rozhdestvensky |year=1965 |title=Growth changes in Asian dinosaurs and some problems of their taxonomy |journal=Paleontological Journal |volume=3 |pages=95–109}}</ref>

== Description ==
[[File:Gorgoscale.svg|left|thumb|''G. libratus'' adult and subadult with a human for scale]]

''Gorgosaurus'' was smaller than ''Tyrannosaurus'' or ''Tarbosaurus'', close in size to ''Albertosaurus''. Adults reached {{convert|8|to|9|m|ft|abbr=on}} in length from snout to tail,<ref name=russell1970>{{cite journal |last=Russell |first=Dale A. |author-link=Dale Russell |year=1970 |title=Tyrannosaurs from the Late Cretaceous of western Canada |journal=National Museum of Natural Sciences Publications in Paleontology |volume=1 |pages=1–34}}</ref><ref name=holtz2004>{{Cite book|last=Holtz |first=Thomas R. |author-link=Thomas R. Holtz Jr. |year=2004 |chapter=Tyrannosauroidea |editor= Weishampel, David B. |editor-link= David B. Weishampel |editor2=Dodson, Peter |editor2-link=Peter Dodson |editor3=Osmólska Halszka |title=The Dinosauria |edition=Second |publisher=University of California Press |location=Berkeley |pages=111–136 |isbn=978-0-520-24209-8}}</ref><ref>{{Cite book|last=Paul|first=Gregory S.|url=http://worldcat.org/oclc/985402380|title=The Princeton Field Guide to Dinosaurs|year=2016|publisher=Princeton University Press|isbn=978-1-78684-190-2|oclc=985402380|pages=110}}</ref> and weighed {{convert|2|-|3|MT|ST}} in body mass.<ref>{{cite book|editor1=Larson, P.|editor2=Carpenter, K.|year=2008|title=''Tyrannosaurus rex'', the Tyrant King (Life of the Past)|pages=310|isbn=9780253350879|publisher=Indiana University Press}}</ref><ref name=seebacher2001>{{cite journal |last=Seebacher |first=Frank |year=2001 |title=A new method to calculate allometric length-mass relationships of dinosaurs |journal=Journal of Vertebrate Paleontology |volume=21 |issue=1 |pages=51–60 |doi=10.1671/0272-4634(2001)021[0051:ANMTCA]2.0.CO;2 |issn=0272-4634|url=http://dinoweb.ucoz.ru/_fr/4/A_new_method_to.pdf |citeseerx=10.1.1.462.255 |s2cid=53446536 }}</ref><ref name=Campione_etal_2014>{{cite journal|last1=Campione|first1=Nicolas E.|last2=Evans|first2=David C.|last3=Brown|first3=Caleb M.|last4=Carrano|first4=Matthew T.|title=Body mass estimation in non-avian bipeds using a theoretical conversion to quadruped stylopodial proportions|journal=Methods in Ecology and Evolution|date=2014|volume=5|issue=9|doi=10.1111/2041-210X.12226|pages=913–923|bibcode=2014MEcEv...5..913C |s2cid=84317234 |doi-access=free}}</ref> The largest known skull measures {{convert|99|cm|in|abbr=on}} long, just slightly smaller than that of ''Daspletosaurus''.<ref name=russell1970/> As in other tyrannosaurids, the skull was large compared to its body size, although chambers within the skull bones and large openings ([[Fenestra (anatomy)|fenestra]]e) between bones reduced its weight. ''Albertosaurus'' and ''Gorgosaurus'' share proportionally longer and lower skulls than ''Daspletosaurus'' and other tyrannosaurids. The end of the snout was blunt, and the [[nasal bone|nasal]] and [[parietal bone]]s were fused along the midline of the skull, as in all other members of the family. The [[orbit (anatomy)|eye socket]] was circular rather than oval or keyhole-shaped as in other tyrannosaurid genera. A tall crest rose from the [[lacrimal bone]] in front of each eye, similar to ''Albertosaurus'' and ''Daspletosaurus''.<ref name=holtz2004/> Differences in the shape of bones surrounding the brain set ''Gorgosaurus'' apart from ''Albertosaurus''.<ref name=currie2003a>{{cite journal |last=Currie |first=Philip J. |author-link=Phil Currie |year=2003 |title=Cranial anatomy of tyrannosaurids from the Late Cretaceous of Alberta |journal=Acta Palaeontologica Polonica |volume=48 |issue=2 |pages=191–226 |url=http://www.app.pan.pl/article/item/app48-191.html?pdf=39 |format=PDF}}</ref>

[[File:Gorgosaurus 2022 Life Reconstruction.png|thumb|[[Life restoration]]]]''Gorgosaurus'' teeth were typical of all known tyrannosaurids. The eight [[premaxilla]]ry teeth at the front of the snout were smaller than the rest, closely packed and ''D''-shaped in [[Cross section (geometry)|cross section]]. In ''Gorgosaurus'', the first tooth in the [[maxilla]] was also shaped like the premaxillary teeth. The rest of the teeth were oval in cross section, rather than blade-like as in most other theropods.<ref name=holtz2004/> Along with the eight premaxillary teeth, ''Gorgosaurus'' had 26 to 30&nbsp;maxillary teeth and 30 to 34&nbsp;teeth in the [[dentary bone]]s of the lower jaw. This number of teeth is similar to ''Albertosaurus'' and ''Daspletosaurus'' but is fewer than those of ''Tarbosaurus'' or ''Tyrannosaurus''.<ref name=currieetal2003>{{cite journal |last=Currie |first=Philip J. |author2=Hurum, Jørn H |author3=Sabath, Karol |author-link=Phil Currie |year=2003 |title=Skull structure and evolution in tyrannosaurid phylogeny |journal=Acta Palaeontologica Polonica |volume=48 |issue=2 |pages=227–234 |url=http://www.app.pan.pl/archive/published/app48/app48-227.pdf }}</ref>[[File:Dr. Bob Bakker with Dino.jpg|thumb|[[Robert T. Bakker|Bob Bakker]] and a skeleton with several bone injuries, from the "Dinosaur Mummy: CSI" exhibit at the HMNS]]
''Gorgosaurus'' shared its general body plan with all other tyrannosaurids. Its massive head was perched on the end of an ''S''-shaped neck. In contrast to its large head, its forelimbs were very small. The forelimbs had only two digits, although a third [[metacarpal]] is known in some specimens, the [[vestigial]] remains of the third digit seen in other theropods. ''Gorgosaurus'' had four digits on each hindlimb, including a small first toe ([[hallux]]) which did not contact the ground. Tyrannosaurid hindlimbs were long relative to overall body size compared with other theropods.<ref name="holtz2004" /> The largest known ''Gorgosaurus'' [[femur]] measured {{convert|105|cm|in|abbr=on}} long. In several smaller specimens of ''Gorgosaurus'', the [[tibia]] was longer than the femur, a proportion typical of [[cursorial|fast-running]] animals.<ref name="russell1970" /> The two bones were of equal length in the largest specimens.<ref name="matthewbrown1923">{{cite journal |last=Matthew |first=William D. |author-link=William Diller Matthew |author2=Brown, Barnum |author2-link=Barnum Brown |year=1923 |title=Preliminary notices of skeletons and skulls of Deinodontidae from the Cretaceous of Alberta |journal=American Museum Novitates |issue=89 |pages=1–9 |hdl=2246/3207 |hdl-access=free }}</ref> The long, heavy tail served as a [[counterweight]] to the head and torso and placed the [[center of gravity]] over the hips.<ref name="holtz2004" />

In 2001, paleontologist [[Phil Currie]] reported skin impressions from the holotype specimen of ''G. libratus''. He originally reported the skin as being essentially smooth and lacking the scales found in other dinosaurs, similar to the secondarily featherless skin found in large modern birds.<ref name="currie2001lecture">Currie, P. (2001). 2001 A. Watson Armour Symposium: The Paleobiology and Phylogenetics of Large Theropods. Field Museum of Natural History, Chicago.</ref> Scales of some sort were present in this specimen, but they are reportedly widely dispersed from each other and very small. Other patches of isolated ''Gorgosaurus'' skin shows denser, and larger though still relatively fine scales (smaller than [[hadrosaurid]] scales and approximately as fine as a Gila monster's).<ref name="DML">Holtz, T. 2001. Phil Currie celebration, tyrant skin, and other things. Dinosaur Mailing List post. http://dml.cmnh.org/2001Jul/msg00243.html {{Webarchive|url=https://web.archive.org/web/20200801090823/http://dml.cmnh.org/2001Jul/msg00243.html |date=August 1, 2020 }}. Accessed: March 15, 2014</ref> Neither of these specimens was associated with any particular bone or specific body area.<ref name="DML" /> In the ''Encyclopedia of Dinosaurs'' [[Kenneth Carpenter]] pointed out that traces of skin impressions from the tail of ''Gorgosaurus'' showed similar small rounded or hexagonal scales.<ref>{{Cite book|last=Carpenter |first=Kenneth |year=1997 |chapter=Tyrannosauridae |editor=Currie, Philip J. |editor-link=Phil Currie |editor2=Padian Kevin |title=Encyclopedia of Dinosaurs |publisher= Academic Press |location=San Diego |pages=768 |isbn=978-0-12-226810-6}}</ref>

== Classification and systematics ==
''Gorgosaurus'' is [[biological classification|classified]] in the theropod [[subfamily]] Albertosaurinae within the [[family (biology)|family]] Tyrannosauridae. It is most closely related to the slightly younger ''Albertosaurus''.<ref name="currieetal2003" /> These are the only two definite albertosaurine genera that have been described, although other undescribed species may exist.<ref name="currie2003a" /> ''[[Appalachiosaurus]]'' was described as a [[basal (phylogenetics)|basal]] [[tyrannosauroid]] just outside Tyrannosauridae,<ref name="carretal2005">{{cite journal |last=Carr |first=Thomas D. |author-link=Thomas Carr (paleontologist) |author2=Williamson, Thomas E. |author3=Schwimmer, David R. |year=2005 |title=A new genus and species of tyrannosauroid from the Late Cretaceous (middle Campanian) Demopolis Formation of Alabama |journal=Journal of Vertebrate Paleontology |volume=25 |issue=1 |pages=119–143 |doi=10.1671/0272-4634(2005)025[0119:ANGASO]2.0.CO;2 |s2cid=86243316 |issn=0272-4634|url=http://www.bioone.org/doi/pdf/10.4202/app.2012.0003 |url-access=subscription }}</ref> although American paleontologist [[Thomas R. Holtz Jr.|Thomas Holtz]] published a phylogenetic analysis in 2004 which indicated it was an albertosaurine.<ref name="holtz2004" /> More recent, unpublished work by Holtz agrees with the original assessment.<ref name="holtzdml2005">{{Cite web |url=http://dml.cmnh.org/2005Sep/msg00345.html |title=RE: Burpee Conference (LONG) |access-date=June 18, 2007 |last=Holtz |first=Thomas R. |author-link=Thomas R. Holtz Jr. |date=September 20, 2005 |archive-date=April 12, 2016 |archive-url=https://web.archive.org/web/20160412171657/http://dml.cmnh.org/2005Sep/msg00345.html |url-status=dead }}</ref> All other tyrannosaurid genera, including ''Daspletosaurus'', ''Tarbosaurus'' and ''Tyrannosaurus'', are classified in the subfamily Tyrannosaurinae. Compared to the tyrannosaurines, albertosaurines had slender builds, with proportionately smaller, lower skulls and longer bones of the lower leg ([[tibia]]) and feet ([[metatarsal]]s and [[phalanges]]).<ref name="currieetal2003" /><ref name="currie2003b">{{cite journal|last=Currie |first=Philip J. |author-link=Phil Currie |year=2003 |title=Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia |journal=Canadian Journal of Earth Sciences |volume=40 |issue=4 |pages=651–665 |doi=10.1139/e02-083|bibcode=2003CaJES..40..651C |url=http://doc.rero.ch/record/14325/files/PAL_E1505.pdf }}</ref>

The close similarities between ''Gorgosaurus libratus'' and ''Albertosaurus sarcophagus'' have led many experts to combine them into one genus over the years. ''Albertosaurus'' was named first, so by convention it is given [[Principle of Priority|priority]] over the name ''Gorgosaurus'', which is sometimes considered its [[junior synonym]]. [[William Diller Matthew]] and [[Barnum Brown]] doubted the distinction of the two genera as early as 1922.<ref name="matthewbrown1922">{{cite journal |last=Matthew |first=William D. |author-link=William Diller Matthew |author2=Brown, Barnum |author2-link=Barnum Brown |year=1922 |title=The family Deinodontidae, with notice of a new genus from the Cretaceous of Alberta |journal=Bulletin of the American Museum of Natural History |volume=46 |issue=6 |pages=367–385 |hdl=2246/1300 }}</ref> ''Gorgosaurus libratus'' was formally reassigned to ''Albertosaurus'' (as ''Albertosaurus libratus'') by [[Dale Russell]] in 1970,<ref name="russell1970" /> and many subsequent authors followed his lead.<ref name="carretal2005" /><ref name="paul1988">{{Cite book |last=Paul |first=Gregory S. |author-link=Gregory S. Paul |year=1988 |title=Predatory Dinosaurs of the World |publisher=Simon & Schuster |location=New York |isbn=978-0-671-61946-6 |page=[https://archive.org/details/predatorydinosau00paul/page/464 464pp] |url=https://archive.org/details/predatorydinosau00paul/page/464 }}</ref> Combining the two greatly expands the geographical and chronological range of the genus ''Albertosaurus''. Other experts maintain the two genera as separate.<ref name="holtz2004" /> Canadian paleontologist [[Phil Currie]] claims there are as many anatomical differences between ''Albertosaurus'' and ''Gorgosaurus'' as there are between ''Daspletosaurus'' and ''Tyrannosaurus'', which are almost always kept separate. He also notes that undescribed tyrannosaurids discovered in [[Alaska]], [[New Mexico]] and elsewhere in North America may help clarify the situation.<ref name="currie2003a" /> [[Gregory S. Paul]] has suggested that ''Gorgosaurus libratus'' is ancestral to ''Albertosaurus sarcophagus''.<ref name="Paul2010">Paul. G.S. ''The Princeton Field Guide to Dinosaurs'', Princeton University Press, 2010. P. 105.</ref>

[[File:Gorgosaurus in Japan.jpg|thumb|right|Skeletal mount in Japan]]
Below is the cladogram of Tyrannosauridae based on the [[phylogenetic analysis]] conducted by Loewen ''et al.'' in 2013.<ref name="Loewen13">{{Cite journal | last1 = Loewen | first1 = M.A. | author-link = Mark Loewen| last2 = Irmis | first2 = R.B. | author-link2 = Randall B. Irmis| last3 = Sertich | first3 = J.J.W. | author-link3 = Joseph Sertich| last4 = Currie | first4 = P. J. | author-link4 = Philip J. Currie| last5 = Sampson | first5 = S. D. | author-link5 = Scott D. Sampson| year = 2013| title = Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans | editor-last = Evans | editor-first = David C| editor-link = David C. Evans (paleontologist)| journal = [[PLoS ONE]] | volume = 8 | issue = 11 | pages = e79420 | doi = 10.1371/journal.pone.0079420 | pmid = 24223179| pmc = 3819173| ref = {{sfnRef|Loewen ''et al.''|2013}}| bibcode = 2013PLoSO...879420L| doi-access = free }}</ref>

{{clade| style=font-size:100%; line-height:100%
|label1=[[Tyrannosauridae]]
|1={{clade
   |1={{clade
      |1='''''Gorgosaurus libratus'''''
      |2=''[[Albertosaurus sarcophagus]]'' }}
   |label2=[[Tyrannosaurinae]]
   |2={{clade
      |1=[[Dinosaur Park Formation|Dinosaur Park]] tyrannosaurid
      |2={{clade
         |1=''[[Daspletosaurus torosus]]''
         |2={{clade
            |1=[[Two Medicine Formation|Two Medicine]] tyrannosaurid
            |2={{clade
               |1=''[[Teratophoneus curriei]]''
               |2={{clade
                  |1=''[[Bistahieversor sealeyi]]''
                  |2={{clade
                     |1=''[[Lythronax argestes]]''
                     |2={{clade
                        |1=''[[Tyrannosaurus rex]]''
                        |2={{clade
                           |1=''[[Tarbosaurus bataar]]''
                           |2=''[[Zhuchengtyrannus magnus]]'' }} }} }} }} }} }} }} }} }} }}

== Paleobiology ==

===Diet and feeding===

[[File:Gorgosaurus TMP 2009.12.14.jpg|thumb|''Gorgosaurus'' juvenile specimen TMP 2009.12.14, featuring stomach contents comprising remains of ''[[Citipes]]'']]
Just like other tyrannosaurids, bite force of ''Gorgosaurus'' and ''Albertosaurus'' increases slowly among young individuals, and then it increases exponentially when they reach the late juvenile stage.<ref name="TZVT21" /> In 2012, Jovannelly and Lane estimated that ''Gorgosaurus'' could exert a bite force of at least 22,000, possibly up to 42,000 newtons.<ref>{{cite journal |last1=Jovanelly |first1=Tamie J. |last2=Lane |first2=Lesley |title=Comparison of the Functional Morphology of Appalachiosaurus and Albertosaurus |journal=The Open Geology Journal |date=September 2012 |volume=6 |issue=1 |pages=65–71 |doi=10.2174/1874262901206010065|bibcode=2012OGJ.....6...65J |doi-access=free }}</ref> Other paleontologists have produced significantly lower bite force estimates. In 2021, given that the largest known ''Gorgosaurus'' had a similar bite force to the similar-sized ''Tyrannosaurus'', Therrien and colleagues proposed that the maximum bite force that could be produced by adult albertosaurines is around 12,200 to 21,800 newtons.<ref name="TZVT21">{{cite journal|author1=Therrien, F.|author2=Zelenitsky, D.K.|author3=Voris, J.T.|author4=Tanaka, K.|year=2021|title=Mandibular force profiles and tooth morphology in growth series of ''Albertosaurus sarcophagus'' and ''Gorgosaurus libratus'' (Tyrannosauridae: Albertosaurinae) provide evidence for an ontogenetic dietary shift in tyrannosaurids|journal=Canadian Journal of Earth Sciences|volume=58|issue=9|pages=812–828|doi=10.1139/cjes-2020-0177|bibcode=2021CaJES..58..812T |s2cid=234026715 |url=https://tspace.library.utoronto.ca/bitstream/1807/106568/1/cjes-2020-0177.pdf}}</ref> In 2022, Sakamoto estimated that ''Gorgosaurus'' had an anterior bite force of 6,418 newtons and a posterior bite force of 13,817 newtons.<ref>{{cite journal | doi=10.7717/peerj.13731 | title=Estimating bite force in extinct dinosaurs using phylogenetically predicted physiological cross-sectional areas of jaw adductor muscles | year=2022 | last1=Sakamoto | first1=Manabu | journal=PeerJ | volume=10 | pages=e13731 | pmid=35846881 | pmc=9285543 | doi-access=free }}</ref>

In 2023, a juvenile ''Gorgosaurus'' (TMP 2009.12.14) with its ''[[in situ]]'' stomach contents containing two ''[[Citipes]]'' juveniles about a year old intact was reported from the [[Dinosaur Park Formation]]. This juvenile would have been 5-7 years old at the time of death, measuring about {{convert|4|m|ft}} long and weighing around {{convert|335|kg|lb}}. It is much larger than the two ''Citipes'' juveniles that weigh about {{convert|9|-|12|kg}}, contrary to the assumption that tyrannosaurids fed on prey of their size once they reached {{convert|16|-|32|kg|lb}}, indicating that juvenile tyrannosaurids still consumed much smaller prey after exceeding a certain size threshold. It’s a direct dietary evidence that reinforces the theory of 'ontogenetic dietary shift' for tyrannosaurids, as previously inferred by ecological modeling and anatomical features among different age groups. Only the remains of the hindlimbs and caudal vertebrae of juvenile ''Citipes'' were present in the tyrannosaurid's stomach cavity, suggesting that a juvenile ''Gorgosaurus'' may have had preferential consumption of the muscular hindlimbs.<ref>{{Cite journal|last1=Therrien |first1=F. |last2=Zelenitsky |first2=D. K. |last3=Tanaka |first3=K. |last4=Voris |first4=J. T. |last5=Erickson |first5=G. M. |last6=Currie |first6=P. J. |last7=DeBuhr |first7=C. L. |last8=Kobayashi |first8=Y. |title=Exceptionally preserved stomach contents of a young tyrannosaurid reveal an ontogenetic dietary shift in an iconic extinct predator |year=2023 |journal=Science Advances |volume=9 |issue=49 |pages=eadi0505 |doi=10.1126/sciadv.adi0505 |pmid=38064561 |doi-access=free |bibcode=2023SciA....9I.505T |pmc=10846869 }}</ref><ref name="NYT-20231208">{{cite news |last=Greshko |first=Michael |title=A Tyrannosaur Was Found Fossilized, and So Was Its Last Meal - A 75-million-year-old Gorgosaurus fossil is the first tyrannosaur skeleton ever found with a filled stomach. |url=https://www.nytimes.com/2023/12/08/science/tyrannosaur-last-meal-gorgosaurus.html |date=December 8, 2023 |work=[[The New York Times]] |url-status=live |archiveurl=https://archive.today/20231208191652/https://www.nytimes.com/2023/12/08/science/tyrannosaur-last-meal-gorgosaurus.html |archivedate=December 8, 2023 |accessdate=December 9, 2023 }}</ref> [[Thomas R. Holtz Jr.]], a paleontologist who also previously theorized that tyrannosaurs underwent a big dietary shift with maturation, said that the fossil "looks like it was Thanksgiving," as the juvenile ''Gorgosaurus'' was mostly eating the legs of ''Citipes''.<ref>{{Cite news |last=Johnson |first=Carolyn |date=December 8, 2023 |title=Young tyrannosaur died with a full stomach, remarkable fossil reveals |url=https://www.washingtonpost.com/science/2023/12/08/tyrannosaurus-fossil-stomach-contents/ |access-date=January 6, 2024 |newspaper=Washington Post}}</ref>

=== Life history ===
[[File:Tyrannosauridae growth rates.svg|thumb|left|A graph showing the hypothesized growth curves (body mass versus age) of four tyrannosaurids. ''Gorgosaurus'' is shown in blue.]]
[[Gregory Erickson (paleontologist)|Gregory Erickson]] and colleagues have studied the growth and life history of tyrannosaurids using bone [[histology]], which can determine the age of a specimen when it died. A growth curve can be developed when the ages of various individuals are plotted against their sizes on a graph. Tyrannosaurids grew throughout their lives, but underwent tremendous growth spurts for about four years, after an extended juvenile phase. [[Sexual maturity]] may have ended this rapid growth phase, after which growth slowed down considerably in adult animals. Examining five ''Gorgosaurus'' specimens of various sizes, Erickson calculated a maximum growth rate of about {{convert|50|kg|lb|abbr=on}} per year during the rapid growth phase, slower than in tyrannosaurines like ''Daspletosaurus'' and ''Tyrannosaurus'', but comparable to ''Albertosaurus''.<ref name="ericksonetal2004">{{cite journal |last1=Erickson|first1=Gregory M. |last2=Makovicky|first2=Peter J. |last3=Currie|first3= Philip J. |author3-link=Phil Currie |last4=Norell|first4= Mark A. |last5=Yerby|first5=Scott A. |last6=Brochu|first6= Christopher A. |year=2004 |title=Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs |journal=Nature |volume=430 |pages=772–775 |doi=10.1038/nature02699 |pmid=15306807 |issue=7001|bibcode=2004Natur.430..772E |s2cid=4404887 |url=http://doc.rero.ch/record/15279/files/PAL_E2578.pdf }}{{Erratum|doi=10.1038/nature16487|pmid=26675726|http://retractionwatch.com/2016/03/01/high-profile-critic-slams-nature-letters-about-dinosaur-growth-following-corrections/ ''Retraction Watch''}}</ref>

''Gorgosaurus'' spent as much as half its life in the juvenile phase before ballooning up to near-maximum size in only a few years.<ref name="ericksonetal2004" /> This, along with the complete lack of predators intermediate in size between huge adult tyrannosaurids and other small theropods, suggests that these niches may have been filled by juvenile tyrannosaurids. This pattern is seen in modern [[Komodo dragon]]s, whose hatchlings start off as tree-dwelling [[insectivore]]s and slowly mature into massive [[apex predator]]s capable of taking down large vertebrates.<ref name="holtz2004" /> Other tyrannosaurids, including ''Albertosaurus'', have been found in aggregations that some have suggested to represent mixed-age [[pack hunter|packs]], but there is no evidence of gregarious behavior in ''Gorgosaurus''.<ref name="currieetal2005">{{Cite book|last=Currie |first=Philip J. |author-link=Phil Currie |author2=Trexler, David |author3=Koppelhus, Eva B. |author3-link=Eva Koppelhus |author4=Wicks, Kelly |author5=Murphy, Nate |year=2005 |chapter=An unusual multi-individual tyrannosaurid bonebed in the Two Medicine Formation (Late Cretaceous, Campanian) of Montana (USA) |editor=Carpenter, Kenneth |editor-link=Kenneth Carpenter |title=The Carnivorous Dinosaurs |publisher=Indiana University Press |location=Bloomington |pages=313–324 |isbn=978-0-253-34539-4}}</ref><ref name="tankecurrie1998">{{cite journal|last=Tanke |first=Darren H. |author2=Currie, Philip J. |author2-link=Phil Currie |year=1998 |title=Head-biting behavior in theropod dinosaurs: paleopathological evidence |journal=Gaia |volume=15 |pages=167–184 |url=http://www.mnhn.ul.pt/geologia/gaia/12.pdf |url-status=dead |archive-url=https://web.archive.org/web/20080227134632/http://www.mnhn.ul.pt/geologia/gaia/12.pdf |archive-date=February 27, 2008 }} [not printed until 2000]</ref> 

[[File:Gorgosaurus libratus (TMP 91.36.500).jpg|thumb|Restoration of a sub-adult]] 
The discovery of two exceptionally preserved juvenile skulls from ''Gorgosaurus'' suggests that ''Gorgosaurus'' underwent the morphological shift from gracile juveniles to robust adults at an earlier age than ''Tyrannosaurus'', to which it was compared in a study published by Jared Voris ''et al.,'' suggests that the ontogenetic changes occurred at roughly 5-7 years of age in ''Gorgosaurus''; much earlier than its larger and later relative. However, both tyrannosaur genera underwent these ontogenetic transformations at a similar percent of skull length relative to the large known adult individuals. The study's results likewise indicate that there is a dissociation between body size and cranial development in tyrannosaurs, while simultaneously allowing better identification of juvenile remains that may have been misidentified in museum fossil collections.<ref>{{Cite journal |last1=Voris |first1=Jared T. |last2=Zelenitsky |first2=Darla K. |last3=Therrien |first3=François |last4=Ridgely |first4=Ryan C. |last5=Currie |first5=Philip J. |last6=Witmer |first6=Lawrence M. |date=2021 |title=Two exceptionally preserved juvenile specimens of Gorgosaurus libratus (Tyrannosauridae, Albertosaurinae) provide new insight into the timing of ontogenetic changes in tyrannosaurids |journal=Journal of Vertebrate Paleontology |volume=41 |issue=6 |at=e2041651 |doi=10.1080/02724634.2021.2041651 |bibcode=2021JVPal..41E1651V |s2cid=248197540 |issn=0272-4634}}</ref> It is estimated that an ontogenetic dietary shift of ''Gorgosaurus'' and ''Albertosaurus'' occurs when the mandibular length reaches {{cvt|58|cm|ft}}, indicating that this is the stage when their bite force increases exponentially and when they begin to pursuit large prey.<ref name="TZVT21" />
=== Paleopathology ===
{{Main|Paleopathology}}
[[File:Tyrrell Gorgosaurus.jpg|thumb|Sub-adult specimen TMP91.36.500 in "[[death pose]]", [[Royal Tyrrell Museum of Palaeontology]]]]
Several pathologies have been documented in the ''Gorgosaurus libratus'' [[holotype]], NMC 2120. These include the third right dorsal rib, as well as healed fractures on the 13th and 14th gastralia and left fibula. Its fourth left metatarsal bore roughened [[exostoses]] both in the middle and at the far end. The third phalanx of the third right toe is deformed, as the claw on that digit has been described as "quite small and amorphous". The three pathologies may have been received in a single encounter with another dinosaur.<ref name="rothschild-dino">Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p.&nbsp;331–336.</ref>

{{multiple image
| align             = right
| direction         = vertical
| header            = TMP 2017.012.0002
| width             = 190
| image1            = Royal Tyrell pathological Gorgosaurus right maxilla..jpg
| image2            = Schematic diagram exhibit of Royal Tyrrell pathological Gorgosaurus right maxilla.jpg
| caption2          = ''Gorgosaurus'' right maxilla with 5 raised scars; healed bite marks.
}}

Another specimen cataloged as [[Royal Tyrrell Museum of Palaeontology|TMP]]94.12.602 bears multiple pathologies. A {{convert|10|cm|in|abbr=on}} [[Anatomical terms of location|longitudinal]] fracture is present in the middle of the right fibula's shaft. Multiple ribs bear healed fractures and the specimen had a [[pseudoarthortic]] [[gastralium]]. Lesions from a bite received to the face were present and showed evidence that the wounds were healing before the animal died.<ref name="rothschild-dino" />

Another specimen has a poorly healed fracture of the right [[fibula]], which left a large [[callus]] on the bone. In a 2001 study conducted by Bruce Rothschild and other paleontologists, 54 foot bones referred to ''Gorgosaurus'' were examined for signs of [[stress fracture]], but none were found.<ref name="rothschild-dino" /><ref name="molnar-pathology">Molnar, R. E., 2001, Theropod paleopathology: a literature survey: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p.&nbsp;337–363.</ref>

As with many tyrannosaurids, several ''Gorgosaurus'' specimens show evidence of [[Intraspecific competition|intraspecific]] face biting.<ref name=":0">{{Cite journal |last1=Brown |first1=Caleb M. |last2=Currie |first2=Philip J. |last3=Therrien |first3=François |date=February 2022 |title=Intraspecific facial bite marks in tyrannosaurids provide insight into sexual maturity and evolution of bird-like intersexual display |url=https://www.cambridge.org/core/journals/paleobiology/article/intraspecific-facial-bite-marks-in-tyrannosaurids-provide-insight-into-sexual-maturity-and-evolution-of-birdlike-intersexual-display/4AC2A6108BC1CE8E849280D9BC4BD9BB |journal=Paleobiology |language=en |volume=48 |issue=1 |pages=12–43 |doi=10.1017/pab.2021.29 |bibcode=2022Pbio...48...12B |issn=0094-8373|url-access=subscription }}</ref>
[[File:Daspletosaurus with bite marks.jpg|alt=TMP 1994.143.1, the skull of a juvenile tyrannosaur from the Dinosaur Park Formation previously thought to be Daspletosaurus sp. but since 2019 assigned to Gorgosaurus libratus. The arrows point at various tyrannosaur bite marks.|thumb|[[Royal Tyrrell Museum of Palaeontology|TMP]] 1994.143.1, the skull of a juvenile tyrannosaur from the [[Dinosaur Park Formation]] previously thought to be ''[[Daspletosaurus]]'' sp. but since 2019 assigned to ''Gorgosaurus libratus''. The arrows point at various tyrannosaur bite marks.]]
Specimen TMP 1994.143.1, a juvenile skull from the [[Dinosaur Park Formation]] with several tyrannosaur bite marks, was previously believed to be ''[[Daspletosaurus]]'' sp.<ref>{{cite journal |last1=Currie |first1=Philip J. |title=Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia |journal=Canadian Journal of Earth Sciences |date=April 2003 |volume=40 |issue=4 |pages=651–665 |doi=10.1139/e02-083 |bibcode=2003CaJES..40..651C |url=https://cdnsciencepub.com/doi/10.1139/e02-083}}</ref><ref>{{cite journal |last1=Currie |first1=Philip J. |title=Cranial anatomy of tyrannosaurid dinosaurs from the Late Cretaceous of Alberta, Canada |journal=Acta Palaeontologica Polonica |date=2003 |volume=48 |issue=2 |pages=191–226 |doi=10.7939/R3M90287B |url=https://era.library.ualberta.ca/items/a9200be3-88e3-44f1-9d54-16ce24393533/view/40dc9dcd-6549-49fb-84eb-0537b748e1ff/APP_48_2003_191.pdf}}</ref><ref>{{cite journal |last1=Hone |first1=David W.E. |last2=Tanke |first2=Darren H. |title=Pre- and postmortem tyrannosaurid bite marks on the remains of ''Daspletosaurus'' (Tyrannosaurinae: Theropoda) from Dinosaur Provincial Park, Alberta, Canada |journal=PeerJ |date=April 9, 2015 |volume=3 |pages=e885 |doi=10.7717/peerj.885 |doi-access=free |pmid=25870775 |pmc=4393819 }}</ref> but was later assigned to ''Gorgosaurus libratus''.<ref>{{cite journal |last1=Voris |first1=Jared T. |last2=Zelenitsky |first2=Darla K. |last3=Therrien |first3=François |last4=Currie |first4=Philip J. |title=Reassessment of a juvenile ''Daspletosaurus'' from the Late Cretaceous of Alberta, Canada with implications for the identification of immature tyrannosaurids |journal=Scientific Reports |date=28 November 2019 |volume=9 |issue=17801 |page=17801 |doi=10.1038/s41598-019-53591-7 |pmid=31780682 |pmc=6882908 |bibcode=2019NatSR...917801V }}</ref><ref>{{cite journal |last1=Coppock |first1=Colton C. |last2=Powers |first2=Mark J. |last3=Voris |first3=Jared T. |last4=Sharpe |first4=Henry S. |last5=Currie |first5=Philip J. |title=Immature ''Daspletosaurus'' sp. specimens from the Dinosaur Park Formation provide insight into ontogenetically invariant tyrannosaurid cranial morphology |journal=Canadian Journal of Earth Sciences |date=26 November 2024 |volume=61 |issue=12 |pages=1227–1239 |doi=10.1139/cjes-2024-0083 |url=https://cdnsciencepub.com/doi/10.1139/cjes-2024-0083|url-access=subscription }}</ref>

TMP 2017.012.0002, is a ''Gorgosaurus'' right maxilla with 5 raised scars; healed injuries from face biting by [[conspecifics]]. <ref name=":0" />

TMP91.36.500 is a very complete sub-adult ''Gorgosaurus'' with preserved face bite injuries and also has a thoroughly healed fracture in the right fibula. Also present was a healed fracture in the dentary and what the authors describing the specimen referred to as "a mushroom-like [[hyperostosis]] of a right pedal phalanx." Ralph Molnar has speculated that this may be the same kind of pathology afflicting an unidentified [[ornithomimid]] discovered with a similar mushroom shaped growth on a toe bone.<ref name="rothschild-dino" /> TMP91.36.500 is also preserved in a characteristic [[death pose]].<ref name="reisdorf2012">{{cite journal | last1 = Reisdorf | first1 = A.G. | last2 = Wuttke | first2 = M. | year = 2012 | title = Re-evaluating Moodie's Opisthotonic-Posture Hypothesis in fossil vertebrates. Part I: Reptiles&nbsp;– The taphonomy of the bipedal dinosaurs ''Compsognathus longipes'' and ''Juravenator starki'' from the Solnhofen Archipelago (Jurassic, Germany) | journal = Palaeobiodiversity and Palaeoenvironments | volume =  92| issue = 1 | pages =  119–168| doi = 10.1007/s12549-011-0068-y | bibcode = 2012PdPe...92..119R | s2cid = 129785393 }}</ref>

== Paleoenvironment ==
[[File:Gorgosaurus chasing Corythosaurus.jpg|thumb|left|Restoration of ''Gorgosaurus'' chasing ''[[Corythosaurus]]'' and ''[[Chasmosaurus]]'']]
Most specimens of ''Gorgosaurus libratus'' have been recovered from the [[Dinosaur Park Formation]] in Alberta.<ref name=currie2003a/> This formation dates to the middle of the [[Campanian]], between 76.5 and 74.8&nbsp;[[Mega-annum|million years ago]],<ref name=eberth2005>Eberth, D.A. (2005). "The geology." In: Currie, P.J., and Koppelhus, E.B. (eds), ''Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed''. Indiana University Press: Bloomington and Indianapolis, 54–82.</ref> and ''Gorgosaurus libratus'' fossils are known specifically from the lower to middle section of the formation, between 76.6 and 75.1 million years ago.<ref name="arbouratal2009">{{cite journal|author=Arbour, V.M.|author-link=Victoria Arbour|last2=Burns|first2=M.E.|last3=Sissons|first3=R.L.|year=2009|title=A redescription of the ankylosaurid dinosaur ''Dyoplosaurus acutosquameus'' Parks, 1924 (Ornithischia: Ankylosauria) and a revision of the genus|journal=Journal of Vertebrate Paleontology|volume=29|issue=4|pages=1117–1135|doi=10.1671/039.029.0405|bibcode=2009JVPal..29.1117A |s2cid=85665879}}</ref> The [[Two Medicine Formation]] and [[Judith River Formation]] of Montana have also yielded possible ''Gorgosaurus'' remains. At this time, the area was a coastal plain along the western edge of the [[Western Interior Seaway]], which divided North America in half. The [[Laramide Orogeny]] had begun uplifting the [[Rocky Mountains]] to the west, from which flowed great rivers that deposited eroded sediment in vast [[floodplain]]s along the coast.<ref name=englishjohnston2004>{{cite journal |last=English |first=Joseph M. |author2=Johnston, Stephen T. |year=2004 |title=The Laramide Orogeny: what were the driving forces? |journal=International Geology Review |volume=46 |issue=9 |pages=833–838 |url=http://web.uvic.ca/~stj/Assets/PDFs/04%20JE%20%26%20STJ%20IGR%20Laramide.pdf |doi=10.2747/0020-6814.46.9.833 |bibcode=2004IGRv...46..833E |s2cid=129901811 |access-date=November 11, 2010 |archive-date=June 7, 2011 |archive-url=https://web.archive.org/web/20110607041857/http://web.uvic.ca/~stj/Assets/PDFs/04%20JE%20%26%20STJ%20IGR%20Laramide.pdf |url-status=dead }}</ref><ref name=eberth1997>{{Cite book|last=Eberth |first=David A. |year=1997 |chapter=Judith River Wedge |editor=Currie, Philip J. |editor-link=Phil Currie |editor2=Padian, Kevin |title=Encyclopedia of Dinosaurs |publisher= Academic Press |location=San Diego |pages=199–204 |isbn=978-0-12-226810-6}}</ref> The climate was [[subtropical]] with marked seasonality, and periodic droughts sometimes resulted in massive mortality among the great herds of dinosaurs, as represented in the numerous [[bonebed]] deposits preserved in the Dinosaur Park Formation. [[Conifer]]s formed the [[forest canopy]], while the [[understory]] plants consisted of [[fern]]s, [[tree fern]]s and [[angiosperm]]s.<ref name=bramankoppelhus2005>{{Cite book |last=Braman |first=Dennis R. |author2=Koppelhus, Eva B. |year=2005 |chapter=Campanian palynomorphs |title=Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed |editor=Currie, Phillip J. |editor-link=Phil Currie |editor2=Koppelhus, Eva B. |publisher=Indiana University Press |location=Bloomington |pages=[https://archive.org/details/dinosaurprovinci0000unse/page/101 101–130] |isbn=978-0-253-34595-0 |chapter-url=https://archive.org/details/dinosaurprovinci0000unse/page/101 }}</ref> Around 73&nbsp;million years ago, the seaway began to expand, [[Transgression (geology)|transgressing]] into areas formerly above sea level and drowning the Dinosaur Park ecosystem. This transgression, called the Bearpaw Sea, is recorded by the marine sediments of the massive [[Bearpaw Shale]].<ref name=eberth1997/>

The Dinosaur Park Formation preserves a great wealth of vertebrate fossils. A wide variety of fish swam the rivers and [[estuary|estuaries]], including [[gar]]s, [[sturgeon]]s, [[shark]]s and [[Batoidea|ray]]s, among others. [[Frog]]s, [[salamander]]s, [[turtle]]s, [[crocodilia]]ns and [[champsosaur]]s also dwelled in the aquatic habitats. [[Azhdarchid]] [[pterosaur]]s and [[ornithurae|ornithuran birds]] like ''[[Apatornis]]'' flew overhead, while the [[Enantiornithes|enantiornithine bird]] ''[[Avisaurus]]'' lived on the ground alongside [[multituberculate]], [[metatheria]]n and [[eutheria]]n [[mammal]]s. A number of species of terrestrial lizards were also present, including [[Teiidae|whiptail]]s, [[skink]]s, [[varanid|monitors]] and [[Anguidae|alligator lizards]]. Dinosaur fossils in particular are found with unrivaled abundance and diversity. Huge herds of [[Ceratopsidae|ceratopsids]] roamed the floodplains alongside equally large groups of saurolophine and lambeosaurine [[hadrosaur]]s. Other herbivorous groups like [[ornithomimid]]s, [[therizinosaur]]s, [[pachycephalosaur]]s, small [[ornithopod]]s, [[nodosaurid]]s and [[ankylosaurid]]s were also represented. Small predatory dinosaurs like [[oviraptorosaur]]s, [[troodont]]s and [[dromaeosaur]]s hunted smaller prey than the huge tyrannosaurids; ''Daspletosaurus'' and ''Gorgosaurus'', which were two orders of magnitude larger in mass.<ref name=eberth1997/> Intervening predatory niches may have been filled by young tyrannosaurids.<ref name=russell1970/><ref name=holtz2004/><ref name=farlow1976>{{cite journal |last=Farlow |first=James O. |author-link=James Farlow |year=1976 |title=Speculations about the diet and foraging behavior of large carnivorous dinosaurs |journal=American Midland Naturalist |volume=95 |issue=1 |pages=186–191 |doi=10.2307/2424244 |jstor=2424244}}</ref> A ''[[Saurornitholestes]]'' [[dentary]] has been discovered in the Dinosaur Park Formation that bore tooth marks left by the bite of a young tyrannosaur, possibly ''Gorgosaurus''.<ref name="saurornitholetes-bite">Jacobsen, A.R. 2001. Tooth-marked small theropod bone: An extremely rare trace. p.&nbsp;58–63. In: ''Mesozoic Vertebrate Life''. Ed.s Tanke, D. H., Carpenter, K., Skrepnick, M. W. Indiana University Press.</ref>

=== Coexistence with ''Daspletosaurus'' ===
[[File:FMNH Daspletosaurus.jpg|thumb|Dinosaur Park specimen (FMNH PR308) of ''[[Daspletosaurus]]'', mounted at the Field Museum]] 
In the middle stages of the Dinosaur Park Formation, ''Gorgosaurus'' lived alongside a rarer species of tyrannosaurid, ''Daspletosaurus''. This is one of the few examples of two tyrannosaur genera coexisting. Similar-sized predators in modern predator [[Guild (ecology)|guilds]] are separated into different [[ecological niche]]s by anatomical, behavioral or geographical differences that limit competition. Niche differentiation between the Dinosaur Park tyrannosaurids is not well understood.<ref name=farlowpianka2002>{{cite journal |last=Farlow |first=James O. |author-link=James Farlow |author2=Pianka, Eric R. |s2cid=18114585 |year=2002 |title=Body size overlap, habitat partitioning and living space requirements of terrestrial vertebrate predators: implications for the paleoecology of large theropod dinosaurs |journal=Historical Biology |volume=16 |issue=1 |pages=21–40 |doi=10.1080/0891296031000154687|bibcode=2002HBio...16...21F |url=http://doc.rero.ch/record/15105/files/PAL_E2372.pdf }}</ref> In 1970, Dale Russell [[hypothesis|hypothesized]] that the more common ''Gorgosaurus'' actively hunted fleet-footed [[hadrosaurs]], while the rarer and more troublesome [[ceratopsia]]ns and [[ankylosauria]]ns (horned and heavily [[Armour (zoology)|armoured]] dinosaurs) were left to the more heavy built ''[[Daspletosaurus]]''.<ref name=russell1970/> However, a specimen of ''Daspletosaurus'' ([[Old Trail Museum|OTM]] 200) from the contemporaneous [[Two Medicine Formation]] of Montana preserves the digested remains of a juvenile hadrosaur in its gut region,<ref name=varricchio2001>{{cite journal |last=Varricchio |first=David J. |year=2001 |title=Gut contents from a Cretaceous tyrannosaurid: implications for theropod dinosaur digestive tracts |journal=Journal of Paleontology |volume=75 |issue=2 |pages=401–406 |doi=10.1666/0022-3360(2001)075<0401:GCFACT>2.0.CO;2 |s2cid=86113170 |issn=0022-3360|url=http://doc.rero.ch/record/14907/files/PAL_E2049.pdf }}</ref> and another bonebed contains the remains of three ''Daspletosaurus'' along with the remains of at least five hadrosaurs.<ref name=currieetal2005/>

Unlike some other groups of dinosaurs, neither genus was more common at higher or lower elevations than the other.<ref name=farlowpianka2002/> However, ''Gorgosaurus'' appears more common in northern formations like Dinosaur Park, with species of ''Daspletosaurus'' being more abundant to the south. The same pattern is seen in other groups of dinosaurs. Chasmosaurine ceratopsians and saurolophine hadrosaurs are also more common in the Two Medicine Formation of Montana and in southwestern North America during the Campanian, while centrosaurines and lambeosaurines dominate in northern latitudes. Holtz has suggested this pattern indicates shared ecological preferences between tyrannosaurines, chasmosaurines and saurolophines. At the end of the later Maastrichtian stage, tyrannosaurines like ''Tyrannosaurus rex'', [[Saurolophinae|saurolophines]] like ''[[Edmontosaurus]]'' and ''[[Kritosaurus]]'' and chasmosaurines like ''[[Triceratops]]'' and ''[[Torosaurus]]'' were widespread throughout western North America, while lambeosaurines were rare, consisting of a few species like ''[[Hypacrosaurus]]'', and albertosaurines and centrosaurines had gone extinct.<ref name=holtz2004/> However, in the case of the centrosaurines, they had thrived in [[Asia]] with genera like ''[[Sinoceratops]]''.<ref name=xu2010>{{Cite journal|author=Xu, X.|author2=Wang, K.|author3=Zhao, X.|author4=Li, D.|name-list-style=amp|year=2010|title=First ceratopsid dinosaur from China and its biogeographical implications|journal=Chinese Science Bulletin|volume=55|issue=16|pages=1631–1635|doi=10.1007/s11434-009-3614-5|bibcode=2010ChSBu..55.1631X|s2cid=128972108}}</ref> While albertosaurine remains have been found in the [[Hell Creek Formation]], it is most likely these are indeterminate remains belonging to a species of ''Tyrannosaurus''.<ref>{{cite journal|last1=Molnar|first1=R.E.|title=An Albertosaur from the Hell Creek Formation of Montana|journal=Journal of Paleontology|date=January 1980|volume=54|issue=1|pages=102–108|jstor=1304167}}</ref>

== See also ==
* [[Timeline of tyrannosaur research]]

== References ==
{{Reflist|30em}}

== External links ==
* {{Wikispecies-inline|Gorgosaurus|''Gorgosaurus''}}
* {{Commons category-inline|Gorgosaurus|''Gorgosaurus''}}

{{Theropoda|C.}}
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[[Category:Tyrannosauridae]]
[[Category:Dinosaur genera]]
[[Category:Campanian dinosaurs]]
[[Category:Dinosaur Park Formation]]
[[Category:Two Medicine Formation]]
[[Category:Judith River Formation]]
[[Category:Fossil taxa described in 1914]]
[[Category:Taxa named by Lawrence Lambe]]
[[Category:Dinosaurs of Canada]]
[[Category:Dinosaurs of the United States]]