View source for Albertosaurus

{{Short description|Genus of bipedal predatory dinosaur}}
{{Featured article}}
{{pp-move}}
{{Use Canadian English|date=September 2020}}
{{Use mdy dates|date=July 2023}}
{{Speciesbox
| fossil_range = [[Late Cretaceous]] ([[Maastrichtian]]), ~{{fossil range|71|68|earliest=75}}{{period fossil range|Cretaceous|71|68|earliest=75}}<small>Possible [[Campanian]] record</small>

| image = Albertosaurus_sarcophagus_cast.jpg
| image_caption = Mounted cast in the [[Milwaukee Public Museum]]
| display_parents = 2
| genus = Albertosaurus
| parent_authority = [[Henry Fairfield Osborn|Osborn]], 1905
| species = sarcophagus
| authority = Osborn, 1905
| synonyms = *''[[Deinodon]] sarcophagus'' <br/><small>(Osborn, 1905) Matthew & Brown, 1922</small>
*''Albertosaurus arctunguis'' <br/><small>Parks, 1928</small>
*''Deinodon arctunguis'' <br/><small>(Parks, 1928) Kuhn, 1939</small>
}}

'''''Albertosaurus''''' ({{IPAc-en|æ|l|ˌ|b|ɜːr|t|ə|ˈ|s|ɔːr|ə|s}}; meaning "Alberta lizard") is a [[genus]] of large [[tyrannosaurid]] [[theropod]] [[dinosaur]] that lived in northwestern North America during the early to middle [[Maastrichtian]] age of the [[Late Cretaceous]] period, about 71&nbsp;[[million years ago]]. The [[type species]], ''A. sarcophagus'', was apparently restricted in [[range (biology)|range]] to the modern-day [[Canadian province]] of [[Alberta]], after which the genus is named, although an indeterminate species ("cf. ''Albertosaurus'' sp.") has been discovered in the [[Corral de Enmedio Formation|Corral de Enmedio]] and [[Packard Formation]]s of [[Mexico]].<ref name="sullivanlucas-alberto" /> Scientists disagree on the content of the genus and some recognize ''[[Gorgosaurus libratus]]'' as a second species.<ref name=Larson08/><ref name="paul2016"/>

As a tyrannosaurid, ''Albertosaurus'' was a [[biped]]al [[predator]] with short arms, two-fingered hands, and a massive head with dozens of large, sharp teeth, a strong sense of smell, powerful binocular vision, and a bone crushing bite force. It may have even been the [[apex predator]] in its local [[ecosystem]]. While ''Albertosaurus'' was certainly large for a theropod, it was still much smaller than its larger and more famous relative ''[[Tyrannosaurus]]'', growing up to {{convert|8|-|9|m|ft}} in length and weighing {{convert|1.7|-|3.0|MT|ST}}.

Since the first discovery in 1884, [[fossil]]s of more than 30 individuals have been recovered that provide scientists with a more detailed knowledge of ''Albertosaurus'' anatomy than what is available for most other tyrannosaurids. The discovery of 26 individuals in one particular site provides evidence of [[gregarious]] behavior and allows for studies of [[ontogeny]] and [[population biology]]. These are near impossible with lesser-known dinosaurs because their remains are rarer and more fragmentary when compared to those of ''Albertosaurus''.

==History of discovery==

===Naming===
[[File:Tyrrell - Crane Albertosaure.jpg|thumb|left|[[Holotype specimen]] CMN 5600]]
''Albertosaurus'' was named by [[Henry Fairfield Osborn]] in a one-page note at the end of his 1905 description of ''Tyrannosaurus''.<ref>{{Cite journal |last=Osborn |first=H.F. |date=December 31, 1905 |title=Tyrannosaurus and other Cretaceous carnivorous dinosaurs |url=https://zenodo.org/record/1038222 |journal=Bulletin of the American Museum of Natural History |volume=21 |pages=259–265 |doi=10.5281/zenodo.1038222 |archive-date=March 23, 2023 |access-date=March 23, 2023 |archive-url=https://web.archive.org/web/20230323011156/https://zenodo.org/record/1038222 |url-status=live }}</ref> Its namesake is [[Alberta]], the [[Canadian province]] established the very same year where the first remains were found. The generic name also incorporates the [[Ancient Greek|Greek]] word {{lang|grc|σαυρος}}/''sauros'', meaning "lizard", which is the most common suffix in dinosaur names. The [[type species]] is ''Albertosaurus sarcophagus'' and the [[specific name (zoology)|specific name]] is derived from the Ancient Greek term σαρκοφάγος (''{{lang|grc-Latn|sarkophagos}}''), meaning "flesh-eating", and having the same [[etymology]] as the [[sarcophagus|funeral container]] with which it shares its name, which is a combination of the Greek words σαρξ/''{{lang|grc-Latn|sarx}}'' ("flesh") and {{lang|grc|φαγειν}}/''{{lang|grc-Latn|phagein}}'' ("to eat").<ref name="osborn1905">{{cite journal |last=Osborn |first=Henry F. |author-link=Henry Fairfield Osborn |year=1905 |title=''Tyrannosaurus'' and other Cretaceous carnivorous dinosaurs |url=https://digitallibrary.amnh.org/bitstream/handle/2246/1464//v2/dspace/ingest/pdfSource/bul/B021a14.pdf?sequence=1&isAllowed=y |journal=Bulletin of the American Museum of Natural History |volume=21 |issue=3 |pages=259–265 |doi=10.1111/j.1468-5965.2007.00735_17.x |hdl=2246/1464 |archive-date=November 2, 2022 |access-date=January 1, 2023 |archive-url=https://web.archive.org/web/20221102135822/https://digitallibrary.amnh.org/bitstream/handle/2246/1464/v2/dspace/ingest/pdfSource/bul/B021a14.pdf?sequence=1&isAllowed=y |url-status=live }}</ref> More than 30 specimens of all ages are known to science.<ref name=ericksonetal2006/><ref name=currie2003b/>

===Early discoveries===
[[Image:red deer river.jpg|thumb|The [[Red Deer River]] near [[Drumheller]], [[Alberta]]. Almost three-quarters of all ''Albertosaurus'' remains have been discovered alongside the river, in outcrops like the ones on either side of this picture.]]
The [[type specimen]] is a partial skull collected on June 9, 1884, from an [[outcrop]] of the [[Horseshoe Canyon Formation]] alongside the [[Red Deer River]] in Alberta. It was recovered by an expedition of the [[Geological Survey of Canada]], led by the famous [[geologist]] [[Joseph Tyrrell|Joseph Burr Tyrrell]]. Due to a lack of specialised equipment, the almost complete skull could only be partially secured. In 1889, Tyrrell's colleague Thomas Chesmer Weston found an incomplete smaller skull associated with some skeletal material at a location nearby.<ref name=TankeCurrie2010>{{cite journal | last1 = Tanke | first1 = Darren H. | last2 = Currie | first2 = Philip J. | year = 2010 | title = A history of ''Albertosaurus'' discoveries in Alberta, Canada | journal = Canadian Journal of Earth Sciences | volume = 47 | issue = 9| pages = 1197–1211 | doi = 10.1139/e10-057 | bibcode = 2010CaJES..47.1197T }}</ref> The two skulls were assigned to the preexisting species ''Laelaps incrassatus'' by [[Edward Drinker Cope]] in 1892.<ref name=cope1892>{{cite journal |last=Cope |first=Edward D. |author-link=Edward Drinker Cope |year=1892 |title=On the skull of the dinosaurian ''Laelaps incrassatus'' Cope |journal=Proceedings of the American Philosophical Society |volume=30 |pages=240–245}}</ref> Although the name ''Laelaps'' was [[International Code of Zoological Nomenclature|preoccupied]] by a genus of [[mite]] and had been changed to ''[[Dryptosaurus]]'' in 1877 by [[Othniel Charles Marsh]], Cope stubbornly refused to recognize the new name created by his archrival. However, [[Lawrence Lambe]] used the name ''Dryptosaurus incrassatus'' instead of ''Laelaps incrassatus'' when he described the remains in detail in 1903 and 1904,<ref>{{cite journal | last1 = Lambe | first1 = L.M. | year = 1903 | title = On the lower jaw of ''Dryptosaurus incrassatus'' (Cope) | journal = Ottawa Naturalist | volume = 17 | page = 134 }}</ref><ref name=lambe1904>{{cite journal |last=Lambe |first=Lawrence M. |author-link=Lawrence Lambe |year=1904 |title=On ''Dryptosaurus incrassatus'' (Cope) from the Edmonton Series of the Northwest Territory |journal=Contributions to Canadian Palaeontology |volume=3 |pages=1–27|url=https://archive.org/details/LambeL.M.1904.OnDryptosaurusIncrassatuscopeFromTheEdmonton |access-date=August 29, 2010}}</ref> which was a combination first coined by [[Oliver Perry Hay]] in 1902.<ref>Hay, Oliver Perry'', 1902 Bibliography and Catalogue of the Fossil Vertebrata of North America''. Bulletin of the United States Geological Survey, N° 117, Government Printing Office. pp 868</ref>

Shortly later, Osborn pointed out that ''D. incrassatus'' was based on generic tyrannosaurid teeth, so the two Horseshoe Canyon skulls could not be confidently referred to that species. The Horseshoe Canyon skulls also differed markedly from the remains of ''D. aquilunguis'', type species of ''Dryptosaurus'', so Osborn gave them the new name ''Albertosaurus sarcophagus'' in 1905. He did not describe the remains in any great detail, citing Lambe's complete description the year before.<ref name=osborn1905/> Both specimens, the [[holotype]] CMN 5600 and the [[paratype]] CMN 5601, are stored in the [[Canadian Museum of Nature]] in [[Ottawa]]. By the early twenty-first century, some concerns had arisen that, due to the damaged state of the holotype, ''Albertosaurus'' might be a ''[[nomen dubium]]'' that could only be used for the type specimen itself because other fossils could not reliably be assigned to it. However, in 2010, [[Thomas Carr (paleontologist)|Thomas Carr]] established that the holotype, the paratype, and comparable later finds all shared a single common unique trait, or [[autapomorphy]]. The possession of an enlarged pneumatic opening in the back rim of the side of the [[palatine bone]] proves that ''Albertosaurus'' is a valid [[taxon]].<ref>{{cite journal | last1 = Carr | first1 = Thomas D. | year = 2010 | title = A taxonomic assessment of the type series of ''Albertosaurus sarcophagus'' and the identity of Tyrannosauridae (Dinosauria, Coelurosauria) in the ''Albertosaurus'' bonebed from the Horseshoe Canyon Formation (Campanian–Maastrichtian, Late Cretaceous) | journal = Canadian Journal of Earth Sciences | volume = 47 | issue = 9| pages = 1213–1226 | doi = 10.1139/e10-035 | bibcode = 2010CaJES..47.1213C |url=https://www.researchgate.net/publication/233603205 }}</ref>

===Dry Island bone bed===
[[File:Three Albertosaurus sarcophagus teeth, Royal Tyrrell Museum, Drumheller, Alberta, 2025-07-13.jpg|thumb|upright|Teeth from Dry Island and Drumheller, [[Royal Tyrrell Museum]]]] 
On August 11, 1910, American paleontologist [[Barnum Brown]] discovered the remains of a large group of ''Albertosaurus'' at another [[quarry]] alongside the Red Deer River. Because of the large number of bones and the limited time available, Brown's party did not collect every specimen, but made sure to collect remains from all of the individuals that they could identify in the [[bone bed]]. Among the bones deposited in the [[American Museum of Natural History]] collections in New York City are seven sets of right [[metatarsal]]s, along with two isolated toe bones that did not match any of the metatarsals in size. This indicated the presence of at least nine individuals in the quarry. Palaeontologist [[Philip J. Currie]] of the [[Royal Tyrrell Museum of Palaeontology]] rediscovered the bonebed in 1997 and resumed fieldwork at the site, which is now located inside [[Dry Island Buffalo Jump Provincial Park]].<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 |journal=Gaia |volume=15 |pages=271–277 |url=http://www.mnhn.ul.pt/geologia/gaia/21.pdf |access-date=May 3, 2009 |archive-url=https://web.archive.org/web/20090326062833/http://www.mnhn.ul.pt/geologia/gaia/21.pdf |archive-date=March 26, 2009 }} (not printed until 2000)</ref> Further excavation from 1997 to 2005 turned up the remains of 13 more individuals of various ages, including a diminutive two-year-old and a very old individual estimated at over {{convert|10|m|ft|abbr=off}} long. None of these individuals are known from complete skeletons and most are represented by remains in both museums.<ref name=ericksonetal2006/><ref name=ericksonetal2004/> Excavations continued until 2008, when the minimum number of individuals present had been established at 12 (on the basis of preserved elements that occur only once in a skeleton) and at 26 if mirrored elements were counted when differing in size due to [[ontogeny]]. A total of 1,128 ''Albertosaurus'' bones had been secured, which is the largest concentration of large theropod fossils known from the Cretaceous.<ref>{{cite journal | last1 = Eberth | first1 = David A. | last2 = Currie | first2 = Philip J. | year = 2010 | title = Stratigraphy, sedimentology, and taphonomy of the ''Albertosaurus'' bonebed (upper Horseshoe Canyon Formation; Maastrichtian), southern Alberta, Canada | journal = Canadian Journal of Earth Sciences | volume = 47 | issue = 9| pages = 1119–1143 | doi = 10.1139/e10-045 | bibcode = 2010CaJES..47.1119E }}</ref>

===Other discoveries===
[[File:Albertosaurus sarcophagus skull (TMP 1985.098.0001), Royal Tyrrell Museum, Drumheller, Alberta, 2025-07-13.jpg|thumb|left|Skull TMP 1985 098 0001]]
In 1911, Barnum Brown, during the second year of the American Museum of Natural History's operations in Alberta, uncovered a fragmentary partial ''Albertosaurus'' skull at the Red Deer River near Tolman Bridge (specimen AMNH 5222).<ref>Carpenter, K., 1992, "Tyrannosaurids (Dinosauria) of Asia and North America", In: N. Mateer and P.-J. Chen (eds.) ''Aspects of nonmarine Cretaceous geology''. China Ocean Press, Beijing, China, pp. 250–268</ref>

[[William Parks (paleontologist)|William Parks]] described a new species in 1928, ''Albertosaurus arctunguis'', based on a partial skeleton lacking a skull that was excavated by Gus Lindblad and Ralph Hornell near the Red Deer River in 1923,<ref name=parks1928>{{cite journal |last=Parks |first=William A. |author-link=William Parks (paleontologist)|year=1928 |title=''Albertosaurus arctunguis'', a new species of therapodous dinosaur from the Edmonton Formation of Alberta |journal=University of Toronto Studies, Geological Series |volume=25 |pages=1–42}}</ref> but this species has been considered identical to ''A. sarcophagus'' since 1970.<ref name=russell1970/> Parks' specimen (ROM 807) is housed in the [[Royal Ontario Museum]] in [[Toronto]].<ref name=TankeCurrie2010/>

No ''Albertosaurus'' fossils were found from 1926 to 1972, but there has been an increase in findings since then. Apart from the Dry Island bonebed, six more skulls and skeletons have since been discovered in Alberta and are housed in various Canadian museums. Specimen RTMP 81.010.001 was found in 1978 by amateur paleontologist Maurice Stefanuk. RTMP 85.098.001 was found by Stefanuk on June 16, 1985. RTMP 86.64.001 was found in December 1985. RTMP 86.205.001 was found in 1986. RTMP 97.058.0001 was found in 1996 and then there is CMN 11315. Unfortunately, none of these skeletons were found with complete skulls.<ref name=TankeCurrie2010/> Fossils have also been reported from the American states of Montana, New Mexico, [[Wyoming]], and [[Missouri]], but they are doubted to be from ''A. sarcophagus'' and may not even belong to the genus ''Albertosaurus''.<ref name=holtz2004/><ref name=currie2003b/>

Two specimens from "cf ''Albertosaurus'' ".sp" have been found in [[Mexico]] ([[Packard Formation]] and [[Corral de Enmedio Formation]]).<ref name="sullivanlucas-alberto">Listed as "cf. ''Albertosaurus'' sp." "Corral De Enmedio and Packard Formations, Cabollona Group, Sonora, Mexico," in Sullivan and Lucas (2006). Page 16.</ref>

===''Gorgosaurus libratus''===
[[File:Albertosaurus Royal Tyrrell 2.jpg|thumb|''[[Gorgosaurus]]'', which was described as a second species of ''Albertosaurus'', ''A. libratus'' by Dale Russell.]]
In 1913, [[paleontologist]] [[Charles Hazelius Sternberg|Charles H. Sternberg]] recovered another tyrannosaurid skeleton from the slightly older [[Dinosaur Park Formation]] in Alberta. Lawrence Lambe named this dinosaur ''[[Gorgosaurus]] libratus'' in 1914.<ref name=lambe1914>{{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 the skull of ''Stephanosaurus marginatus'' from the same horizon |journal=Ottawa Naturalist |volume=28 |pages=13–20}}</ref> Other specimens were later found in Alberta and the US state of [[Montana]]. Finding no significant differences to separate the two taxa (due mostly to a lack of good ''Albertosaurus'' skull material), [[Dale Russell]] declared the name ''Gorgosaurus'' a [[junior synonym]] of ''Albertosaurus'', which had been named first, and ''G. libratus'' was renamed ''Albertosaurus libratus'' in 1970. A species distinction was maintained because of the age difference. The addition extended the temporal range of the genus ''Albertosaurus'' earlier by several million years and its geographic range southwards by hundreds of kilometres.<ref name=russell1970/>

In 2003, [[Philip J. Currie]], benefiting from much more extensive finds and a general increase in anatomical knowledge of theropods, compared several tyrannosaurid skulls and came to the conclusion that the two species are more distinct than previously thought. As the two species are [[sister taxa]], they are more closely related to each other than to any other species of tyrannosaurid. Recognizing this, Currie nevertheless recommended that ''Albertosaurus'' and ''Gorgosaurus'' be kept as separate genera, as he concluded that they were no more similar than ''Daspletosaurus'' and ''Tyrannosaurus'', which are almost always separated. In addition to this, several albertosaurine specimens have been recovered from [[Alaska]] and [[New Mexico]]. Currie suggested that the ''Albertosaurus''-''Gorgosaurus'' situation may be clarified once these are fully described.<ref name=currie2003b/> Most authors have followed Currie's recommendation,<ref name=holtz2004/><ref name=ericksonetal2004/><ref name=ricklefs2007>{{cite journal |last=Ricklefs |first=Robert E. |year=2007 |title=Tyrannosaur ageing |journal=Biology Letters |volume=3 |issue=2 |pages=214–217 |doi=10.1098/rsbl.2006.0597 |pmid=17284406 |pmc=2375931}}</ref> but some have not.<ref name=carretal2005/>

===Other species===
In 1930, Anatoly Nikolaevich Riabinin named ''Albertosaurus pericolosus'' based on a tooth from China that probably belonged to ''[[Tarbosaurus]]''.<ref>{{cite journal | last1 = Riabinin | first1 = A.N. | year = 1930 | title = [In Russian] "On the age and fauna of the dinosaur beds on the Amur River | journal = Memoirs of the Russian Mineralogical Society | volume = 59 | issue = 2| pages = 41–51 }}</ref> In 1932, [[Friedrich von Huene]] renamed ''Dryptosaurus incrassatus'', not considered a ''nomen dubium'' by him, to ''Albertosaurus incrassatus''.<ref>Von Huene, F.'', 1932 Die fossile Reptil-Ordnung Saurischia: ihre Entwicklung und Geschichte''. Monographie für Geologie und Palaeontologie, Parts I and II, ser. I, 4: 1–361</ref> Because he had identified ''Gorgosaurus'' with ''Albertosaurus'', in 1970, Russell also renamed ''Gorgosaurus sternbergi'' (Matthew & Brown 1922) into ''Albertosaurus sternbergi'' and ''Gorgosaurus lancensis'' (Gilmore 1946) into ''Albertosaurus lancensis''.<ref name=russell1970/> The former species is today seen as a juvenile form of ''Gorgosaurus libratus'' and the latter is seen as either identical to ''[[Tyrannosaurus]]'' or representing a separate genus, ''[[Nanotyrannus]]''. In 1988, [[Gregory S. Paul]] based ''Albertosaurus megagracilis'' on a small tyrannosaurid skeleton, specimen LACM 28345, from the [[Hell Creek Formation]] of Montana.<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 |url-access=registration |url=https://archive.org/details/predatorydinosau00paul }}</ref> It was renamed ''[[Dinotyrannus]]'' in 1995,<ref name=olshevsky1995>{{cite journal |last=Olshevsky |first=George. |author-link=George Olshevsky |year=1995 |title=(The origin and evolution of the tyrannosaurids.) |journal=Kyoryugaku Saizensen (Dino Frontline) |volume=9 |pages=92–119 |language=ja}}</ref> but is now thought to represent a juvenile ''Tyrannosaurus''.<ref name=currie2003a/> Also in 1988, Paul renamed ''[[Alectrosaurus]] olseni'' (Gilmore 1933) into ''Albertosaurus olseni'',<ref name=paul1988/> but this has found no general acceptance. In 1989, ''Gorgosaurus novojilovi'' (Maleev 1955) was renamed by Bryn Mader and Robert Bradley as ''Albertosaurus novojilovi''.<ref>{{cite journal | last1 = Mader | first1 = B. | last2 = Bradley | first2 = R. | year = 1989 | title = A redescription and revised diagnosis of the syntypes of the Mongolian tyrannosaur ''Alectrosaurus olseni'' | journal = Journal of Vertebrate Paleontology | volume = 9 | issue = 1| pages = 41–55 | doi=10.1080/02724634.1989.10011737| bibcode = 1989JVPal...9...41M }}</ref>

On two occasions, species based on valid ''Albertosaurus'' material were reassigned to a different genus, ''[[Deinodon]]''. In 1922, [[William Diller Matthew]] renamed ''A. sarcophagus'' into ''Deinodon sarcophagus''.<ref>{{cite journal | last1 = Matthew | first1 = W.D. | last2 = Brown | first2 = B. | 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 }}</ref> In 1939, German paleontologist [[Oskar Kuhn]] renamed ''A. arctunguis'' into ''Deinodon arctunguis''.<ref>Kuhn, O.'', 1939 Saurischia — Fossilium catalogus I, Animalia, Pars 87''. 's-Gravenhage, W. Junk, 1939, 124 pp</ref>

==Description==
[[File:Albertoscale.svg|thumb|Size comparison]]
''Albertosaurus'' was a fairly large bipedal predator, but smaller than ''[[Tarbosaurus]]'' and ''Tyrannosaurus''. Typical ''Albertosaurus'' adults measured up to {{convert|8|-|9|m|ft|abbr=on}} long<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 name="paul2016"/> and weighed between {{convert|1.7|and|3.0|MT|ST}} in body mass.<ref name=christiansenfarina2004>{{cite journal |last=Christiansen |first=Per |author2=Fariña, Richard A. |year=2004 |title=Mass prediction in theropod dinosaurs |journal=Historical Biology |volume=16 |issue=2–4 |pages=85–92 |doi=10.1080/08912960412331284313|bibcode=2004HBio...16...85C |s2cid=84322349 }}</ref><ref name="paul2016">{{cite book|last=Paul|first=G.S.|year=2016|title=The Princeton Field Guide to Dinosaurs|edition=Second|publisher=Princeton University Press|page=112|isbn=978-0-691-16766-4}}</ref><ref>{{cite journal|last1=Campione|first1=N. E.|last2=Evans|first2=D. C.|last3=Brown|first3=C. M.|last4=Carrano|first4=M. T.|date=2014|title=Body mass estimation in non-avian bipeds using a theoretical conversion to quadruped stylopodial proportions|journal=Methods in Ecology and Evolution|volume=5|issue=9|pages=913−923|doi=10.1111/2041-210X.12226|doi-access=free|bibcode=2014MEcEv...5..913C |hdl=10088/25281}}</ref><ref name=Larson08>{{cite book|editor1=Larson, P.|editor2=Carpenter, K.|year=2008|title=''Tyrannosaurus rex'', the Tyrant King (Life of the Past)|page=310|isbn=978-0-253-35087-9|publisher=Indiana University Press}}</ref>

''Albertosaurus'' shared a similar body appearance with all other tyrannosaurids, ''Gorgosaurus'' in particular. Typical for a theropod, ''Albertosaurus'' was bipedal and balanced its large, heavy head and [[torso]] with a long, muscular tail. However, tyrannosaurid forelimbs were extremely small for their body size and retained only two functional fingers, the second being longer than the first. The legs were long and ended in a four-toed foot on which the first toe, the [[hallux]], was very short and did not reach the ground. The third <!--'(middle)' - with four digits, here is no middle one; instead, there are two middle ones: the 2nd & 3rd.--> toe was longer than the rest.<ref name=holtz2004/> ''Albertosaurus'' may have been able to reach walking speeds of 14–21&nbsp;km/hour (8–13&nbsp;mi/hour).<ref>{{cite journal |last1= Thulborn |first1= Richard A. |year=1982 |title= Speeds and gaits of dinosaurs |journal= Palaeogeography, Palaeoclimatology, Palaeoecology | volume=38 |issue= 3–4 |pages=227–256 |doi=10.1016/0031-0182(82)90005-0 |bibcode= 1982PPP....38..227T }}</ref> At least for the younger individuals, a high running speed is plausible.<ref name=currie1998/>

Two skin impressions from ''Albertosaurus'' are known, and both show [[Scale (anatomy)|scales]]. One patch was found associated with some gastralic ribs and the impression of a long, unknown bone, indicating that the patch is from the belly. The scales are pebbly and gradually become larger and somewhat hexagonal in shape. Also preserved are two larger feature scales, placed 4.5&nbsp;centimeters apart from each other,<ref name=":0">{{Cite journal |last1=Bell |first1=Phil |last2=E. Campione |first2=Nicolás |last3=Scott Persons |first3=W |last4=J. Currie |first4=Philip |last5=Larson |first5=Peter |last6=Tanke |first6=Darren |last7=T. Bakker |first7=Robert |date=June 1, 2017 |title=Tyrannosauroid integument reveals conflicting patterns of gigantism and feather evolution |journal=Biology Letters |volume=13 |issue=6 |article-number=20170092 |doi=10.1098/rsbl.2017.0092 |pmc=5493735 |pmid=28592520}}</ref> making ''Albertosaurus'', along with ''[[Carnotaurus]]'', the only known theropods with preserved feature scales.<ref>{{Cite journal |last1=Hendrickx |first1=Christophe |last2=Bell |first2=Phil R. |last3=Pittman |first3=Michael |last4=Milner |first4=Andrew R. C. |last5=Cuesta |first5=Elena |last6=O'Connor |first6=Jingmai |last7=Loewen |first7=Mark |last8=Currie |first8=Philip J. |last9=Mateus |first9=Octávio |last10=Kaye |first10=Thomas G. |last11=Delcourt |first11=Rafael |date=June 2022 |title=Morphology and distribution of scales, dermal ossifications, and other non-feather integumentary structures in non-avialan theropod dinosaurs |url=https://onlinelibrary.wiley.com/doi/10.1111/brv.12829 |journal=Biological Reviews |language=en |volume=97 |issue=3 |pages=960–1004 |doi=10.1111/brv.12829 |pmid=34991180 |s2cid=245820672 |issn=1464-7931 |archive-date=September 28, 2022 |access-date=September 27, 2022 |archive-url=https://web.archive.org/web/20220928224916/https://onlinelibrary.wiley.com/doi/10.1111/brv.12829 |url-status=live |url-access=subscription }}</ref> Another skin impression is from an unknown part of the body. These scales are small, diamond-shaped, and arranged in rows.<ref name=":0" />

===Skull and teeth===
[[File:Albertosaurus sarcophagus skull (TMP 2019.000.0023, detail), Royal Tyrrell Museum, Drumheller, Alberta, 2025-07-13 02.jpg|thumb|left|Skull cast at the [[Royal Tyrrell Museum of Palaeontology]] in [[Drumheller, Alberta]]]]
The massive [[skull]] of ''Albertosaurus'', which was perched on a muscular, short, S-shaped neck, was about {{convert|1|m|ft|abbr=off}} long in the largest adults.<ref name=currie2003a>{{cite journal |last=Currie |first=Philip J. |author-link=Philip J. 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 |archive-date=December 23, 2023 |access-date=January 3, 2023 |archive-url=https://web.archive.org/web/20231223034524/https://doc.rero.ch/record/14325/files/PAL_E1505.pdf |url-status=live }}</ref> Wide openings in the skull, called [[fenestra]]e, provided space for [[muscle]] attachment sites and [[sensory organ]]s that reduced its overall weight. Its long jaws contained, both sides combined, 58 or more banana-shaped teeth. Larger tyrannosaurids possessed fewer teeth, but ''[[Gorgosaurus]]'' had 62. Unlike most theropods, ''Albertosaurus'' and other tyrannosaurids were [[heterodont]], with teeth of different forms depending on their position in the mouth. The [[premaxilla]]ry teeth at the tip of the upper jaw, four per side, were much smaller than the rest, more closely packed, and D-shaped in [[cross section (geometry)|cross section]].<ref name=holtz2004/> Like with ''Tyrannosaurus'', the maxillary (cheek) teeth of ''Albertosaurus'' were adapted in general form to resist lateral forces exerted by a struggling prey animal. The bite force of ''Albertosaurus'' was less formidable, however, with the maximum force, by the back teeth, reaching 3,413 Newtons.<ref>{{cite journal | last1 = Reichel | first1 = Miriam | year = 2010 | title = The heterodonty of ''Albertosaurus sarcophagus'' and ''Tyrannosaurus rex'': biomechanical implications inferred through 3-D models | journal = Canadian Journal of Earth Sciences | volume = 47 | issue = 9| pages = 1253–1261 | doi = 10.1139/e10-063 | bibcode = 2010CaJES..47.1253R }}</ref> Above the eyes were short bony crests that may have been brightly coloured in life and possibly used, by males in particular, in courtship to attract a mate.<ref name="ageofdinosaursalbertosaurus">"Albertosaurus." In: Dodson, Peter; Britt, Brooks; Carpenter, Kenneth; Forster, Catherine A.; Gillette, David D.; Norell, Mark A.; Olshevsky, George; Parrish, J. Michael; & Weishampel, David B. ''The Age of Dinosaurs''. Lincolnwood, Illinois: Publications International, Ltd., 1993. pp.&nbsp;106–107. {{ISBN|0-7853-0443-6}}.</ref>

[[File:Albertosaurus sarcophagus.png|thumb|[[Life restoration]]]]
In 2001, [[William Abler]] observed that ''Albertosaurus'' [[tooth serrations]] resemble a [[Fracture|crack]] in the tooth ending in a round void called an ampulla.<ref name="abler-2001">Abler, W.L. 2001. A kerf-and-drill model of tyrannosaur tooth serrations. p.&nbsp;84–89. In: ''Mesozoic Vertebrate Life''. Ed.s Tanke, D. H., Carpenter, K., Skrepnick, M. W. Indiana University Press.</ref> Tyrannosaurid teeth were used as holdfasts for pulling flesh off a body, so when a tyrannosaur pulled back on a piece of meat, the tension could cause a purely crack-like serration to spread through the tooth.<ref name="abler-2001" /> However, the presence of the ampulla distributed these forces over a larger [[surface area]] and lessened the risk of damage to the tooth under strain.<ref name="abler-2001" /> The presence of incisions ending in voids has parallels in human engineering. Guitar makers use incisions ending in voids to, as Abler describes, "impart alternating regions of flexibility and rigidity" to wood that they work on.<ref name="abler-2001" /> The use of a [[drill]] to create an "ampulla" of sorts and prevent the propagation of cracks through material is also used to protect aircraft surfaces.<ref name="abler-2001" /> Abler demonstrated that a plexiglass bar with incisions called "kerfs" and drilled holes was more than 25% stronger than one with only regularly placed incisions.<ref name="abler-2001" /> Unlike tyrannosaurs, more ancient predators, like [[phytosaur]]s and ''[[Dimetrodon]]'', had no adaptations to prevent the crack-like serrations of their teeth from spreading when subjected to the forces of feeding.<ref name="abler-2001" />

==Classification and systematics==
''Albertosaurus'' is a member of the theropod [[Family (taxonomy)|family]] Tyrannosauridae, specifically the subfamily Albertosaurinae. Its closest relative is the slightly older ''Gorgosaurus libratus'' (sometimes called ''Albertosaurus libratus''; see below).<ref name=currieetal2003>{{cite journal |last=Currie |first=Philip J. |author2=Hurum, Jørn H|author3=Sabath, Karol |author-link=Philip J. Currie|year=2003 |title=Skull structure and evolution in tyrannosaurid phylogeny |journal=Acta Palaeontologica Polonica | volume=48 |issue=2 |pages=227–234 |url=http://app.pan.pl/archive/published/app48/app48-227.pdf|access-date=May 3, 2009| archive-url= https://web.archive.org/web/20090326062829/http://app.pan.pl/archive/published/app48/app48-227.pdf| archive-date= March 26, 2009 | url-status= live}}</ref> These two species are the only described albertosaurines, but other undescribed species may exist.<ref name=currie2003b>{{cite journal |last=Currie |first=Philip J. |author-link=Philip J. 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://app.pan.pl/archive/published/app48/app48-191.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://app.pan.pl/archive/published/app48/app48-191.pdf |archive-date=October 9, 2022 |url-status=live }}</ref> [[Thomas R. Holtz Jr.|Thomas Holtz]] found ''[[Appalachiosaurus]]'' to be an albertosaurine in 2004,<ref name=holtz2004/> but his more recent unpublished work places it as a basal eotyrannosaurian just outside of Tyrannosauridae,<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=live }}</ref> in agreement with other authors.<ref name=carretal2005>{{cite journal |last=Carr |first=Thomas D. |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 |url=http://www.bioone.org/doi/pdf/10.4202/app.2012.0003 |url-access=subscription }}</ref>

The other major subfamily of tyrannosaurids is Tyrannosaurinae, which includes members like ''[[Daspletosaurus]]'', ''[[Tarbosaurus]]'', and ''Tyrannosaurus''. Compared with the more robust tyrannosaurines, albertosaurines had slender builds, with proportionately smaller skulls and longer bones of the lower legs ([[tibia]]) and feet ([[metatarsal]]s and [[phalanges]]).<ref name=currie2003a/><ref name=currieetal2003/>
[[File:Albertosaurus Clean.png|thumb|upright|Cast in the [[Rocky Mountain Dinosaur Resource Center]] in Woodland Park, Colorado]] 
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 | article-number = e79420 | doi = 10.1371/journal.pone.0079420 | pmid =  24223179| pmc = 3819173| bibcode = 2013PLoSO...879420L | ref = {{sfnRef|Loewen ''et al.''|2013}}| 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=''[[Daspletosaurus horneri]]''
            |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]]'' }} }} }} }} }} }} }} }} }} }}

==Palaeobiology==

===Growth pattern===
[[Image:Tyrannosauridae growth rates.svg|thumb|300px|A graph showing the hypothesized growth curves (body mass versus age) of four tyrannosaurids, with ''Albertosaurus'' drawn in <span style="color:red">red</span><ref name=ericksonetal2004>{{cite journal |last=Erickson |first=Gregory M. |author2=Makovicky, Peter J. |author3=Currie, Philip J. |author4=Norell, Mark A. |author5=Yerby, Scott A. |author6=Brochu, 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://www.biology.ualberta.ca/courses.hp/biol506.hp/pdfs/Erickson'04_Nature.pdf |access-date=August 29, 2010 |archive-url=https://web.archive.org/web/20111006045136/http://www.biology.ualberta.ca/courses.hp/biol506.hp/pdfs/Erickson%2704_Nature.pdf |archive-date=October 6, 2011 }}{{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>]]
Most age categories of ''Albertosaurus'' are represented in the [[fossil record]]. Using bone [[histology]], the age of an individual animal at the time of death can often be determined, allowing growth rates to be estimated and compared with other species. The youngest known ''Albertosaurus'' is a two-year-old discovered in the Dry Island bonebed, which would have weighed about 50 kilograms (110&nbsp;[[pound (mass)|lb]]) and measured slightly more than {{convert|2|m|ft|abbr=off}} long. The {{convert|10|m|ft|abbr=off}} specimen from the same quarry is 28 years old, the oldest and largest one known. When specimens of intermediate age and size are plotted on a graph, an ''S''-shaped growth curve results, with the most rapid growth occurring in a four-year period ending around the sixteenth year of life, a pattern also seen in other tyrannosaurids. The growth rate during this phase was {{convert|122|kg|lb|abbr=off}} per year, based on an adult weighing 1.3&nbsp;[[tonne]]s. Other studies have suggested higher adult weights, which would affect the magnitude of the growth rate, but not the overall pattern. Tyrannosaurids similar in size to ''Albertosaurus'' had similar growth rates, although the much larger ''Tyrannosaurus'' grew at almost five times this rate ({{convert|601|kg|lb|abbr=off|disp=sqbr}} per year) at its peak.<ref name=ericksonetal2006/> The end of the rapid growth phase suggests the onset of [[sexual maturity]] in ''Albertosaurus'', although growth continued at a slower rate throughout the animals' lives.<ref name=ericksonetal2006>{{cite journal|last=Erickson |first=Gregory M. |author2=Currie, Philip. J. |author3=Inouye, Brian D. |author4=Wynn, Alice A. |year=2006 |title=Tyrannosaur life tables: an example of nonavian dinosaur population biology |journal=Science |volume=313 |pages=213–217 |doi=10.1126/science.1125721 |pmid=16840697 |issue=5784 |bibcode=2006Sci...313..213E |s2cid=34191607 |url=http://www.nceas.ucsb.edu/jai/podcast_publications/inouye_science_dinosaur.pdf |access-date=August 29, 2010 |archive-url=https://web.archive.org/web/20100718143500/http://www.nceas.ucsb.edu/jai/podcast_publications/inouye_science_dinosaur.pdf |archive-date=July 18, 2010 }}</ref><ref name=ericksonetal2004/> Sexual maturation while still actively growing appears to be a shared trait among small<ref name=ericksonetal2007>{{cite journal|last=Erickson |first=Gregory M. |author2=Curry Rogers, Kristi|author3=Varricchio, David J.|author4=Norell, Mark.|author5=Xu, Xing |year=2007 |title=Growth patterns in brooding dinosaurs reveals the timing of sexual maturity in non-avian dinosaurs and genesis of the avian condition |journal=Biology Letters |volume=3 |pages=558–561 |doi=10.1098/rsbl.2007.0254 |pmid=17638674 |issue=5 |pmc=2396186}}</ref> and large<ref name=lee_werning2008>{{cite journal |last=Lee |first=Andrew H. |author2=Werning, Sarah |year=2008 |title=Sexual maturity in growing dinosaurs does not fit reptilian growth models |journal=PNAS |volume=105 |pages=582–587 |doi=10.1073/pnas.0708903105 |pmid=18195356 |issue=2 |pmc=2206579|bibcode=2008PNAS..105..582L |doi-access=free }}</ref> dinosaurs, as well as in large mammals like humans and [[elephant]]s.<ref name=lee_werning2008/> This pattern of relatively early sexual maturation differs strikingly from the pattern in birds, which delay their sexual maturity until after they have finished growing.<ref name=ricklefs2007/><ref name=lee_werning2008/>

During growth, thickening of the tooth morphology changed so much that, had the association of young and adult skeletons on the Dry Island bonebed not proven that they belonged to the same taxon, the teeth of juveniles would likely have been identified by statistical analysis as those of a different species.<ref>{{cite journal | last1 = Buckley | first1 = Lisa G. | last2 = Larson | first2 = Derek W. | last3 = Reichel | first3 = Miriam | last4 = Samman | first4 = Tanya | year = 2010 | title = Quantifying tooth variation within a single population of ''Albertosaurus sarcophagus'' (Theropoda: Tyrannosauridae) and implications for identifying isolated teeth of tyrannosaurids | journal = Canadian Journal of Earth Sciences | volume = 47 | issue = 9| pages = 1227–1251 | doi = 10.1139/e10-029 | bibcode = 2010CaJES..47.1227B }}</ref>

===Life history===
[[File:Edmontosaurus pounding Albertosaurus by durbed.jpg|thumb|left|Restoration of ''[[Edmontosaurus]]'' fighting off ''Albertosaurus'']]
Most known ''Albertosaurus'' individuals were aged 14 years or older at the time of death. Juvenile animals are rarely fossilized for several reasons, mainly [[preservation bias]], where the smaller bones of younger animals were less likely to be preserved by fossilization than the larger bones of adults, and collection bias, where smaller fossils are less likely to be noticed by collectors in the field.<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> Young ''Albertosaurus'' are relatively large for juvenile animals, but their remains are still rare in the fossil record when compared to adults. It has been suggested that this phenomenon is a consequence of [[Biological life cycle|life history]], rather than bias, and that fossils of juvenile ''Albertosaurus'' are rare because they simply did not die as often as adults did.<ref name=ericksonetal2006/>

A hypothesis of ''Albertosaurus'' life history postulates that [[hatchling]]s died in large numbers, but have not been preserved in the fossil record because of their small size and fragile construction. After just two years, juveniles were larger than any other predator in the region, aside from adult ''Albertosaurus'', and more fleet-footed than most of their prey animals. This resulted in a dramatic decrease in their mortality rate and a corresponding rarity of fossil remains. Mortality rates doubled at age twelve, perhaps the result of the physiological demands of the rapid growth phase, and then doubled again with the onset of sexual maturity between the ages of fourteen and sixteen. This elevated mortality rate continued throughout adulthood, perhaps due to the high physiological demands of procreation, including stress and injuries received during intraspecific competition for mates and resources, and the eventual, ever-increasing effects of [[senescence]]. The higher mortality rate in adults may explain their more common preservation. Very large animals were rare because few individuals survived long enough to attain such size. High infant mortality rates, followed by reduced mortality among juveniles and a sudden increase in mortality after sexual maturity, with very few animals reaching maximum size, is a pattern observed in many modern large mammals, including elephants, [[African buffalo]], and [[rhinoceros]]. The same pattern is also seen in other tyrannosaurids. The comparison with modern animals and other tyrannosaurids lends support to this life history hypothesis, but bias in the fossil record may still play a large role, especially since more than two-thirds of all ''Albertosaurus'' specimens are known from the exact same locality.<ref name=ericksonetal2006/><ref name=ricklefs2007/><ref>{{cite journal | last1 = Erickson | first1 = Gregory M. | last2 = Currie | first2 = Philip J. | last3 = Inouye | first3 = Brian D. | last4 = Winn | first4 = Alice A. | year = 2010 | title = A revised life table and survivorship curve for ''Albertosaurus sarcophagus'' based on the Dry Island mass death assemblage | journal = Canadian Journal of Earth Sciences | volume = 47 | issue = 9| pages = 1269–1275 | doi = 10.1139/e10-051 | bibcode = 2010CaJES..47.1269E }}</ref>

===Social behaviour===
[[Image:Albertosaurus Tyrrell.jpg|thumb|Bronze sculptures of a pack, RTM, designed by Brian Cooley]]
The Dry Island bonebed discovered by Barnum Brown and his crew contains the remains of 26 ''Albertosaurus'', the most individuals found in one locality of any large Cretaceous theropod and the second-most of any large theropod dinosaur behind the ''[[Allosaurus]]'' assemblage at the [[Cleveland-Lloyd Dinosaur Quarry]] in [[Utah]]. The group seems to be composed of one very old adult, eight adults between 17 and 23 years old, seven sub-adults undergoing their rapid growth phases at between 12 and 16 years old, and six juveniles between the ages of 2 and 11 years old that had not yet reached the growth phase.<ref name=ericksonetal2006/>

The near-absence of [[herbivore]] remains and the similar state of preservation common to the many individuals at the ''Albertosaurus'' bonebed quarry led Currie to conclude that the locality was not a predator trap, such as the [[La Brea Tar Pits]] in [[California]], and that all of the preserved animals died at the same time. Currie claims this as evidence of pack behavior.<ref name="currie1998"/> Other scientists are skeptical, observing that the animals may have been driven together by a drought, flood, or other reasons.<ref name=ericksonetal2006/><ref name=roachbrinkman2007/><ref name=eberthmccrea2001>{{cite journal |last=Eberth |first=David A. |author2=McCrea, Richard T. |year=2001 |title=Were large theropods gregarious? |journal=Journal of Vertebrate Paleontology |volume=21 |issue=Supplement to 3 – Abstracts of Papers, 61st Annual Meeting of the Society of Vertebrate Paleontology |page=46A|doi=10.1080/02724634.2001.10010852|s2cid=220414868 }}(published abstract only)</ref>

[[File:Albertosaurus hunting Saurolophus.jpg|thumb|left|Two ''Albertosaurus'' hunting ''[[Saurolophus]]'']]
There is plentiful evidence for gregarious behaviour among herbivorous dinosaurs, including [[ceratopsia]]ns and [[hadrosaur]]s.<ref name=horner1997>{{cite book |last=Horner |first=John R. |author-link=Jack Horner (paleontologist) |year=1997 |chapter=Behavior |editor=Currie, Philip J. |editor-link=Philip J. Currie |editor2=Padian, Kevin |title=Encyclopedia of Dinosaurs |publisher=Academic Press |location=San Diego |pages=45–50 |isbn=978-0-12-226810-6}}</ref> However, only rarely are so many dinosaurian predators found at the same site. Small theropods, like ''[[Deinonychus]]''<ref name=maxwellostrom1995>{{cite journal |doi=10.1080/02724634.1995.10011256 |last=Maxwell |first=W. Desmond |author2=Ostrom, John H. |author-link2=John Ostrom |year=1995 |title=Taphonomy and paleobiological implications of ''Tenontosaurus''-''Deinonychus'' associations |journal=Journal of Vertebrate Paleontology |volume=15 |issue=4 |pages=707–712|bibcode=1995JVPal..15..707M }}</ref> and ''[[Coelophysis]]'',<ref name=raath1990>{{cite book |last=Raath |first=Michael A. |year=1990 |chapter=Morphological variation in small theropods and its meaning in systematics: evidence from ''Syntarsus rhodesiensis'' |editor=Carpenter, Kenneth |editor-link=Kenneth Carpenter |editor2=Currie, Philip J. |title=Dinosaur Systematics: Approaches and Perspectives |publisher=Cambridge University Press |location=Cambridge |pages=91–105 |isbn=978-0-521-43810-0}}</ref> have been found in aggregations, as have larger predators, such as ''Allosaurus'' and ''[[Mapusaurus]]''.<ref name=coriacurrie2006>{{cite journal|last=Coria |first=Rodolfo A. |author-link=Rodolfo Coria |author2=Currie, Philip J. |year=2006 |title=A new carcharodontosaurid (Dinosauria, Theropoda) from the Upper Cretaceous of Argentina |journal=Geodiversitas |volume=28 |issue=1 |pages=71–118 |url=http://www.mnhn.fr/museum/front/medias/publication/7653_g06n1a4.pdf |access-date=May 3, 2009 |archive-url=https://web.archive.org/web/20090326062832/http://www.mnhn.fr/museum/front/medias/publication/7653_g06n1a4.pdf |archive-date=March 26, 2009 }}</ref> There is some evidence of [[gregarious behaviour]] in other tyrannosaurids as well, as fragmentary remains of smaller individuals were found alongside "[[Sue (dinosaur)|Sue]]", the ''Tyrannosaurus'' mounted in the [[Field Museum of Natural History]] in [[Chicago]], and a bonebed in the [[Two Medicine Formation]] of Montana contains at least three specimens of ''Daspletosaurus'' preserved alongside several hadrosaurs.<ref name=currieetal2005>{{cite book |last=Currie |first=Philip J. |author-link=Philip J. Currie|author2=Trexler, David|author3-link=Eva Koppelhus |author3=Koppelhus, Eva B.|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 |author2-link=David Trexler |editor-link=Kenneth Carpenter |title=The Carnivorous Dinosaurs |publisher=Indiana University Press |location=Bloomington |pages=313–324 |isbn=978-0-253-34539-4}}</ref> These findings may corroborate the evidence for social behaviour in ''Albertosaurus'', although some or all of the above localities may represent temporary or unnatural aggregations.<ref name=currie1998/> Others have speculated that, instead of social groups, at least some of these finds represent [[Komodo dragon]]-like mobbing of carcasses, where aggressive competition leads to some of the predators being killed and even [[cannibal]]ized.<ref name=roachbrinkman2007/> The evidence of cannibalism was later reported in 2024 by Coppock and Currie. The evidence consisted of tooth traces found on the medial surface of a pubis attributed to an albertosaurine, which given the lack of other albertosaurine species in the assemblage almost certainly reflected another ''A. sarcophagus''. These bite traces show no signs of healing and thus strongly indicate that they were made post-mortem and represent feeding marks as opposed to injuries sustained during intraspecific combat.<ref>{{Cite journal |last1=Coppock |first1=Colton C. |last2=Currie |first2=Philip John |date=14 February 2024 |title=Additional ''Albertosaurus sarcophagus'' (Tyrannosauridae, Albertosaurinae) material from the Danek Bonebed of Edmonton, Alberta, Canada with evidence of cannibalism |journal=[[Canadian Journal of Earth Sciences]] |url=https://www.researchgate.net/publication/376475519_ADDITIONAL_ALBERTOSAURUS_SARCOPHAGUS_TYRANNOSAURIDAE_ALBERTOSAURINAE_MATERIAL_FROM_THE_DANEK_BONEBED_OF_EDMONTON_ALBERTA_CANADA_WITH_EVIDENCE_OF_CANNIBALISM |volume=61 |issue=3 |pages=401–407 |doi=10.1139/cjes-2023-0055 |bibcode=2024CaJES..61..401C |s2cid=266279287 |via=ResearchGate |access-date=21 October 2025}}</ref>

Currie has also speculated on the pack-hunting habits of ''Albertosaurus''. The leg proportions of the smaller individuals were comparable to those of [[ornithomimid]]s, which were probably among the fastest dinosaurs. Younger ''Albertosaurus'' were probably equally fleet-footed or at least faster than their prey. Currie hypothesized that the younger members of the pack may have been responsible for driving their prey towards the adults, who were larger and more powerful, but also slower.<ref name=currie1998/> Juveniles may also have had different lifestyles than adults, filling predator [[Ecological niche|niche]]s between the enormous adults and the smaller contemporaneous theropods, the largest of which were two [[orders of magnitude]] smaller than adult ''Albertosaurus'' in mass.<ref name=holtz2004/> A similar situation is observed in modern Komodo dragons, with hatchlings beginning life as small [[insectivore]]s before growing to become the dominant predators on their islands.<ref name=auffenberg1981>{{cite book |last=Auffenberg |first=Walter |author-link=Walter Auffenberg|year=2000 |title=The Behavioral Ecology of the Komodo Monitor |publisher=University Press of Florida |location=Gainesville |isbn=978-0-8130-0621-5}}</ref> However, as the preservation of behaviour in the fossil record is exceedingly rare, these ideas cannot readily be tested. In 2010, Currie, though still favouring the hunting pack hypothesis, admitted that the concentration could have been brought about by other causes, such as a slowly rising water level during an extended flood.<ref>{{cite journal | last1 = Currie | first1 = Philip J. | last2 = Eberth | first2 = David A. | year = 2010 | title = On gregarious behavior in ''Albertosaurus'' | journal = Canadian Journal of Earth Sciences | volume = 47 | issue = 9| pages = 1277–1289 | doi = 10.1139/e10-072 | bibcode = 2010CaJES..47.1277C }}</ref>

===Palaeopathology===
[[File:Common-Avian-Infection-Plagued-the-Tyrant-Dinosaurs-pone.0007288.g002.jpg|thumb|Tyrannosaur jaw-bones with [[trichomonosis]]-type lesions; D (upper right) is ''Albertosaurus'']]
In 2009, researchers hypothesized that smooth-edged holes found in the fossil jaws of [[tyrannosaurid]] dinosaurs, such as ''Albertosaurus'', were caused by a parasite similar to ''[[Trichomonas]] gallinae'', which infects birds.<ref name=Wolff2009>{{cite journal| year = 2009|author1=Wolff, Ewan D. S.|author2=Salisbury, Steven W.|author3=Horner, John R.|author4=Varricchio, David J.| editor1-last = Hansen| editor1-first = Dennis Marinus| title = Common avian infection plagued the tyrant dinosaurs| journal = PLOS ONE| pmid = 19789646| volume = 4 | issue = 9| pmc = 2748709| article-number = e7288| doi = 10.1371/journal.pone.0007288|bibcode=2009PLoSO...4.7288W|doi-access=free}}</ref> They suggested that tyrannosaurids transmitted the infection by biting each other and that the infection impaired their ability to eat.<ref name=Wolff2009/>

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. They found that only one of the 319 ''Albertosaurus'' foot bones checked for stress fractures actually had them and none of the four hand bones did. The scientists found that stress fractures were "significantly" less common in ''Albertosaurus'' than in the [[carnosaur]] ''[[Allosaurus]]''.<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> ROM 807, the holotype of ''A. arctunguis'' (now referred to ''A. sarcophagus''), had a {{convert|abbr=on|2.5 by 3.5|cm|in}} deep hole in the [[iliac blade]], although the describer of the species did not recognize this as pathological. The specimen also contains some [[exostosis]] on the fourth left metatarsal. In 1970, two of the five ''Albertosaurus sarcophagus'' specimens with humeri were reported by Dale Russel as having pathological damage to them.<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>

In 2010, the health of the Dry Island ''Albertosaurus'' assembly was reported upon. Most specimens showed no sign of disease. On three phalanges of the foot, strange bony spurs that consisted of abnormal ossifications of the tendons, so-called [[enthesophyte]]s, were present, but their cause is unknown. Two ribs and a belly-rib showed signs of breaking and healing. One adult specimen had a left lower jaw showing a puncture wound and both healed and unhealed bite marks. The low number of abnormalities compares favourably with the health condition of a ''[[Majungasaurus]]'' population of which it was established, in 2007, that 19% of individuals showed bone pathologies.<ref>{{cite journal | last1 = Bell | first1 = Phil R. | year = 2010 | title = Palaeopathological changes in a population of ''Albertosaurus sarcophagus'' from the Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada | journal = Canadian Journal of Earth Sciences | volume = 47 | issue = 9| pages = 1263–1268 | doi = 10.1139/e10-030 | bibcode = 2010CaJES..47.1263B }}</ref>

==Palaeoecology==
[[Image:Horseshoe Canyon Alberta Nov 1988.jpg|thumb|left|The [[Horseshoe Canyon Formation]] is exposed in its [[Type locality (geology)|type section]] at [[Horseshoe Canyon (Alberta)|Horseshoe Canyon]], [[Alberta]]]]
Most fossils of ''Albertosaurus sarcophagus'' are known from the upper [[Horseshoe Canyon Formation]] in Alberta. These younger units of this [[geologic formation]] date to the early [[Maastrichtian]] age of the [[Late Cretaceous]] period, about 70 to 68 million years ago. Immediately below this formation is the [[Bearpaw Shale]], a [[Marine (ocean)|marine]] formation representing a section of the [[Western Interior Seaway]]. The Inland Sea was receding as the climate cooled and sea levels subsided towards the end of the Cretaceous, thus exposing land that had previously been underwater. It was not a smooth process, however, and the seaway would periodically rise to cover parts of the region throughout Horseshoe Canyon before finally receding altogether in the years after. Due to the changing sea levels, many different environments are represented in the Horseshoe Canyon Formation, including offshore and near-shore marine habitats and coastal habitats, such as [[lagoon]]s, [[estuary|estuaries]], and [[tidal flat]]s. Numerous [[coal]] seams represent ancient [[peat]] [[swamp]]s. Like most of the other [[vertebrate]] fossils from the formation, ''Albertosaurus'' remains are found in deposits laid down in the [[river delta|deltas]] and [[floodplain]]s of large rivers during the later half of Horseshoe Canyon times.<ref name=eberth1997>{{cite book |last=Eberth |first=David A. |year=1997 |chapter=Edmonton Group |editor=Currie, Philip J. |editor-link=Philip J. 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 [[fauna]] of the Horseshoe Canyon Formation is well-known, as vertebrate fossils, including those of dinosaurs, are very common. [[Shark]]s, [[Batoidea|rays]], [[sturgeon]]s, [[bowfin]]s, [[gar]]s, and the gar-like ''[[Aspidorhynchus]]'' made up the fish fauna. Mammals included [[multituberculate]]s and the [[marsupial]] ''[[Didelphodon]]''. The saltwater [[plesiosaur]] ''[[Leurospondylus]]'' has been found in marine sediments in the Horseshoe Canyon, while freshwater environments were populated by [[turtle]]s, ''[[Champsosaurus]]'', and [[crocodilia]]ns like ''[[Leidyosuchus]]'' and ''[[Stangerochampsa]]''. Dinosaurs dominate the fauna, especially hadrosaurs, which make up half of all dinosaurs known. These include the genera ''[[Edmontosaurus]]'', ''[[Saurolophus]]'', and ''[[Hypacrosaurus]]''. Ceratopsians and [[ornithomimid]]s were also very common, together making up another third of the known fauna. Along with much rarer [[ankylosauria]]ns and [[pachycephalosaur]]s, all of these animals would have been prey for a diverse array of carnivorous theropods, including [[troodontid]]s, [[dromaeosaurid]]s, and [[caenagnathid]]s.<ref name=eberth1997/><ref>{{cite journal | last1 = Larson | first1 = Derek W. | last2 = Brinkman | first2 = Donald B. | last3 = Bell | first3 = Phil R. | year = 2010 | title = Faunal assemblages from the upper Horseshoe Canyon Formation, an early Maastrichtian cool-climate assemblage from Alberta, with special reference to the ''Albertosaurus sarcophagus'' bonebed | journal = Canadian Journal of Earth Sciences | volume = 47 | issue = 9| pages = 1159–1181 | doi = 10.1139/e10-005 | bibcode = 2010CaJES..47.1159L }}</ref> Intermingled with the ''Albertosaurus'' remains of the Dry Island bonebed, the bones of the small theropod ''[[Albertonykus]]'' were found.<ref name=LC08>{{cite journal |last=Longrich |first=Nicholas R. |author2=Currie, Philip J. |year=2009 |title=''Albertonykus borealis'', a new alvarezsaur (Dinosauria: Theropoda) from the Early Maastrichtian of Alberta, Canada: Implications for the systematics and ecology of the Alvarezsauridae |journal=Cretaceous Research |volume=30 |issue=1 |pages= 239–252|doi=10.1016/j.cretres.2008.07.005 |bibcode=2009CrRes..30..239L }}</ref> Adult ''Albertosaurus'' were the [[apex predator]]s in their environment, with intermediate niches possibly filled by juvenile ''Albertosaurus''.<ref name=eberth1997/>

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

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

==External links==
* {{Commons category-inline}}

{{Theropoda|C.}}
{{Portal bar|Dinosaurs|Canada}}
{{Taxonbar|from=Q40751}}

[[Category:Tyrannosauridae]]
[[Category:Dinosaur genera]]
[[Category:Maastrichtian dinosaurs]]
[[Category:Horseshoe Canyon Formation]]
[[Category:Dinosaurs of Canada]]
[[Category:Fossil taxa described in 1905]]
[[Category:Taxa named by Henry Fairfield Osborn]]