Editing Albertosaurus (section)

==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 |url-status=dead }}{{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 rex'' 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 |url-status=dead |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 |url-status=dead }}</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 |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.<ref>{{Cite journal |last1=Coppock |first1=C. |last2=Currie |first2=P. J. |year=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 |volume=61 |issue=3 |pages=401–407 |doi=10.1139/cjes-2023-0055 |bibcode=2024CaJES..61..401C |s2cid=266279287 }}</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| pages = 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>