The type specimen is a partial skull, collected in the summer of 1884 from an outcrop of the Horseshoe Canyon Formation alongside the Red Deer River, in Alberta.
This specimen, found on June 9, 1884, was recovered by an expedition of the Geological Survey of Canada, led by the famous geologist 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.
The two skulls were assigned to the preexisting species Laelaps incrassatus by Edward Drinker Cope in 1892, although the name Laelaps was preoccupied by a genus of mite and had been changed to Dryptosaurus in 1877 by Othniel Charles Marsh.
Cope refused to recognize the new name created by his archrival Marsh.
However, Lawrence Lambe used the name Dryptosaurus incrassatus instead of Laelaps incrassatus when he described the remains in detail in 1903 and 1904, a combination first coined by Oliver Perry Hay in 1902.
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 created the new name Albertosaurus sarcophagus for them in 1905.
He did not describe the remains in any great detail, citing Lambe's complete description the year before.
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, a "dubious name" 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 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, proving that Albertosaurus was a valid taxon.
The type specimen is a partial skull, collected in the summer of 1884 from an outcrop of the Horseshoe Canyon Formation alongside the Red Deer River, in Alberta. This specimen, found on June 9, 1884, was recovered by an expedition of the Geological Survey of Canada, led by the famous geologist 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. The two skulls were assigned to the preexisting species Laelaps incrassatus by Edward Drinker Cope in 1892, although the name Laelaps was preoccupied by a genus of mite and had been changed to Dryptosaurus in 1877 by Othniel Charles Marsh. Cope refused to recognize the new name created by his archrival Marsh. However, Lawrence Lambe used the name Dryptosaurus incrassatus instead of Laelaps incrassatus when he described the remains in detail in 1903 and 1904, a combination first coined by Oliver Perry Hay in 1902. 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 created the new name Albertosaurus sarcophagus for them in 1905. He did not describe the remains in any great detail, citing Lambe's complete description the year before. 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, a "dubious name" 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 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, proving that Albertosaurus was a valid taxon.
Albertosaurus