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Albertosaurinae
Albertosaurines, or dinosaurs of the subfamily Albertosaurinae, lived in the Late Cretaceous of USA and Canada. The subfamily was first used by Philip J. Currie, Jørn H. Hurum and Karol Sabath as a group of tyrannosaurid dinosaurs. It was originally defined as "(''Albertosaurus'' + ''Gorgosaurus'')", including only the two genera. The group is sister clade to Tyrannosaurinae. In 2007, it was found that the group also contained ''Maleevosaurus'', often synonymized with ''Tarbosaurus''. However, this classification has not been accepted, and ''Maleevosaurus'' is still considered a juvenile ''Tarbosaurus'' or ''Tyrannosaurus''. Clevenger T. M. McLain found in an abstract, that ''Alioramus'', commonly used as a derived tyrannosauroid, was an albertosaurine, or the sister taxon to the group.
==Description==
Albertosaurines are large, lightly built tyrannosaurids. Compared to tyrannosaurines, they are lightly built, have shorter, flatter skulls, had shorter ilia, and had proportionally longer tibiae. Albertosaurines and tyrannosaurines share arms or about equal length, with the exception of ''Tarbosaurus'', who's arms a shorter for its size.
''Albertosaurus'' was smaller than some other tyrannosaurids, such as ''Tarbosaurus'' and ''Tyrannosaurus''. Typical adults of ''Albertosaurus'' and ''Gorgosaurus'' measured up to long, while rare individuals of ''Albertosaurus'' could grow to over in length. Several independent mass estimates, obtained by different methods, suggest that an adult ''Albertosaurus'' weighed between and . ''Gorgosaurus'' estimates are higher, at around , although greater estimates exist of about .
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. ''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）』
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