Editing Albertosaurus (section)

===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>