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Albertosaurus with a juvenile. See more dinosaur images.

Ann Ronan Picture Library

ALBERTOSAURUS (al-BUR-toh-SORE-us)

Period: Late Cretaceous

Order, Suborder, Family: Saurischia, Theropoda, Tyrannosauridae

Location: North America

Length: 30 feet (9 meters)

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Albertosaurus was an older "cousin" to the better-known Tyrannosaurus. In many ways the two were similar: the head was large compared to the body, the tiny forearms had only two fingers each, and the long tail balanced the body over two powerful back legs. But the eyes of Tyrannosaurus looked forward and those of Albertosaurus looked more toward the sides. This suggests that Albertosaurus did not judge distances as well, so that when it hunted, it probably did not leap onto its prey.

Stealth, power, and speed were its biggest assets. With its long, powerful rear legs, Albertosaurus could outrun its prey or ambush a heavy herbivore that stood alone and unprotected. The rear legs could deliver crushing blows, knocking the prey off balance. It delivered deadly wounds with its claws. The light build and long legs show that it was fast and graceful. It may have been able to run 25-30 miles per hour.

The head of Albertosaurus had two small, blunt horns, just in front of the eyes. These may have been for show, much like the comb on a chicken today. It is possible that the male had brightly colored skin covering the horns to attract the female during mating season. It would be like birds today, with the males brightly colored to attract females.

Fossil remains of Albertosaurus are common, especially teeth, which often broke when it was feeding. Several species are recognized: Albertosaurus sarcophagus and Albertosaurus libratus are the most common. Albertosaurus lancensis has been recently renamed Nanotyrannus. Some paleontologists think the theropod dinosaur Alectrosaurus olseni from Mongolia is a species of Albertosaurus. If this is correct, Albertosaurus lived in both North America and Asia. Albertosaurus may have hunted in packs.