Albertosaurus (/ælˌbɜrtɵˈsɔrəs/; meaning "Alberta lizard") is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, about 70 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. 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 with dozens of large, sharp teeth. It may have been at the top of the food chain in its local ecosystem. Although relatively large for a theropod, Albertosaurus was much smaller than its more famous relative Tyrannosaurus, probably weighing less than 2 metric tons.
Since the first discovery in 1884, fossils of more than thirty 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.