Bradley as Albertosaurus novojilovi. On two occasions, species based on valid Albertosaurus material were reassigned to a different genus: in 1922 William Diller Matthew renamed A. sarcophagus into Deinodon sarcophagus and in 1939 German paleontologist Oskar Kuhn renamed A. arctunguis into Deinodon arctunguis. Description Albertosaurus was a large bipedal predator but smaller than Tarbosaurus and Tyrannosaurus rex. Typical Albertosaurus adults measured up to long, and weighed between in body mass. 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 km/hour (8–13 mi/hour). At least for the younger individuals, a high running speed is plausible. Two skin impressions from Albertosaurus are known, both showing scales. One patch is found associated with some gastralic ribs and the impression of a long, unknown bone, indicating that the patch is from the belly. The scales are pebbly and gradually become larger and somewhat hexagonal in shape. Also preserved are two larger feature scales, placed 4.5 cm apart from each other, making Albertosaurus, along with Carnotaurus, the only known theropods with preserved feature scales. Another skin impression is from an unknown part of the body. These scales are small, diamond-shaped and arranged in rows. Skull and teeth The massive skull of Albertosaurus, which was perched on a short, S-shaped neck, was about long in the largest adults. 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, both sides combined, 58 or more banana-shaped teeth; larger tyrannosaurids possessed fewer teeth; Gorgosaurus had 62. 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, four per side, were much smaller than the rest, more closely packed, and D-shaped in cross section. Like with Tyrannosaurus, the maxillary (cheek) teeth of Albertosaurus were adapted in general form to resist lateral forces