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''Albertosaurus'' (; 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 that had 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 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. ==Description== ''Albertosaurus'' was smaller than some other tyrannosaurids, such as ''Tarbosaurus'' and ''Tyrannosaurus''. Typical ''Albertosaurus'' adults measured up to long, while rare individuals of great age could grow to be over long. Several independent mass estimates, obtained by different methods, suggest that an adult ''Albertosaurus'' weighed between 1.3 tonnes (1.4 short tons) and 1.7 tonnes (1.9 tons). ''Albertosaurus'' shared a similar body appearance with all other tyrannosaurids. Typically for a theropod, ''Albertosaurus'' was bipedal and balanced the heavy head and torso with a long tail. However, tyrannosaurid forelimbs were extremely small for their body size and retained only two digits. The hind limbs were long and ended in a four-toed foot on which the first digit, called the hallux, was short and did not reach the ground. The third digit was longer than the rest.〔 ''Albertosaurus'' may have been able to reach walking speeds of 14−21 kilometres per hour (8−13 miles per hour). At least for the younger individuals, a high running speed is plausible.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Albertosaurus」の詳細全文を読む スポンサード リンク
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