Albertosaurus

Albertosaurus was a relative of Tyrannosaurus. It was smaller than T. rex and lived a few million years earlier. Albertosaurus walked on two legs and had a large head with sharp, saw-toothed teeth. It had two-fingered hands on short arms. Its long tail provided balance and quick turning. It had powerful back legs with clawed, three-toed feet.

Albertosaurus was about 30 feet (9 m) long, about 11 feet (3.4 m) tall at the hips, and up to 3 tons in weight (averaging roughly 2500 kg). Its lower jaw had 14 to 16 teeth; the upper jaw had 17-19 teeth. It had one row of teeth in each jaw and had at least one replacement tooth growing up under each working tooth.

Albertosaurus was more lightly built than Tyrannosaurus. Most Albertosaurus specimens were found in a single place. 

Compared with the robust tyrannosaurines (such as Tarbosaurus and Tyrannosaurus), albertosaurines had slender builds, with proportionately smaller skulls and longer bones of the lower leg (tibia) and feet (metatarsals and phalanges).Currie, Philip J. 2003. Cranial anatomy of tyrannosaurids from the Late Cretaceous of Alberta (PDF). Acta Palaeontologica Polonica 48 (2): 191–226. That suggests they were taking smaller or younger prey than Tyrannosaurus, and were able to run faster to do so.

 References 

Category:Tyrannosaurids