Albertosaurus was a carnivorous (meat-eating) dinosaur that lived in the late Cretaceous period, approximately 76 to 74 million years ago, in North America. It was a bipedal (walking on two legs) creature, with tiny two-fingered hands, and a massive head containing dozens of large sharp teeth.
Albertosaurus was around 26 feet (7.9 meters) long, and weighed approximately 3 tons. It was much smaller than its relative Tyrannosaurus Rex.
The first specimen discovered was a partial skull discovered in 1884 from an outcrop near the Red Deer River in Alberta, Canada, and was initially incorrectly assigned to the the species Dryptosaurus (also known at the tim as "Laelaps incrassatus") by Edward D. Cope. The name Albertosaurus was coined by Henry Fairfield Osborn, in a brief note in his 1905 paper describing Tyrannosaurus Rex.
About 30 fossil specimens of Albertosaurus have been found to date. This includes 22 individuals found at a single site, which is highly suggestive of pack behavior.
Finally, it is worth noting that some paleontologists have suggested that the Asian Tyrannosauroid, Alectrosaurus, may actually be a species of Albertosaurus.