Albertosaurus Arm

Albertosaurus Arm. Dinosaur of Cretaceous Alberta, Canada. 42in/1.1 m length. Royal Ontario Museum skeleton specimen.

Albertosaurus was smaller than the truly gigantic tyrannosaurids like Tarbosaurus and Tyrannosaurus. Typical adults measured up to 9 meters (30 ft) long,[1][2] while rare individuals of great age could grow to over 10 meters (33 ft) in length.[3] 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).

The massive skull of Albertosaurus, perched on a short, S-shaped neck, was approximately 1 meter (3.3 ft) long in the largest adults.[6] Wide openings in the skull (fenestrae) reduced the weight of the head while also providing space for muscle attachment and sensory organs. Its long jaws contained more than 60 banana-shaped teeth; larger tyrannosaurids possessed fewer teeth. Unlike most theropods, Albertosaurus and other tyrannosaurids were heterodont, with teeth of different forms depending on their position in the mouth. The premaxillary teeth at the tip of the upper jaw were much smaller than the rest, more closely packed, and D-shaped in cross section.[2]

All tyrannosaurids, including Albertosaurus, shared a similar body appearance. 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. The first digit, called the hallux, was short and only the other three contacted the ground, with the third (middle) digit longer than the rest.