Albertosaurus (; meaning "Alberta lizard") is a genus of tyrannosaurid theropod dinosaurs that lived in western North America during the Late Cretaceous Period, about 71 million years ago. The type species, A. sarcophagus, was apparently restricted in 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 and Packard Formations in Mexico. Scientists disagree on the content of the genus, with some recognizing Gorgosaurus libratus as a second species. As a tyrannosaurid, Albertosaurus was a bipedal predator with tiny, two-fingered hands and a massive head that had dozens of large, sharp teeth. It may have been an apex predator in its local ecosystem. While Albertosaurus was large for a theropod, it was much smaller than its larger and more famous relative Tyrannosaurus rex, growing up to in length and weighing . Since the first discovery in 1884, fossils of more than 30 individuals have been recovered, providing scientists with a more detailed knowledge of Albertosaurus anatomy than is available for most other tyrannosaurids. The discovery of 26 individuals at one site provides evidence of pack behaviour and allows studies of ontogeny and population biology, which are impossible with lesser-known dinosaurs due to their remains being rarer and more fragmentary compared to those of Albertosaurus. History of discovery Naming Albertosaurus was named by Henry Fairfield Osborn in a one-page note at the end of his 1905 description of Tyrannosaurus rex. Its namesake is Alberta, the Canadian province established the same year, in which the first remains were found. The generic name also incorporates the Greek term /sauros ("lizard"), the most common suffix in dinosaur names. The type species is Albertosaurus sarcophagus; the specific name is derived from Ancient Greek σαρκοφάγος () meaning "flesh-eating" and having the same etymology as the funeral container with which it shares its name: a combination of the Greek words σαρξ/ ("flesh") and / ("to eat"). More than 30 specimens of all ages are known to science. Early discoveries 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 Burr Tyrrell. Due to a lack of specialised equipment the almost complete skull could