 The close similarities between Gorgosaurus libratus and Albertosaurus sarcophagus have led many experts to combine them into one genus over the years . Albertosaurus was named first , so by convention it is given priority over the name Gorgosaurus , which is sometimes considered its junior synonym . William Diller Matthew and Barnum Brown doubted the distinction of the two genera as early as 1922 . Gorgosaurus libratus was formally reassigned to Albertosaurus ( as Albertosaurus libratus ) by Dale Russell in 1970 , and many subsequent authors followed his lead . Combining the two greatly expands the geographical and chronological range of the genus Albertosaurus . Other experts maintain the two genera as separate . Canadian paleontologist Phil Currie claims there are as many anatomical differences between Albertosaurus and Gorgosaurus as there are between Daspletosaurus and Tyrannosaurus , which are almost always kept separate . He also notes that undescribed tyrannosaurids discovered in Alaska , New Mexico and elsewhere in North America may help clarify the situation . Gregory S. Paul has suggested that Gorgosaurus libratus is ancestral to Albertosaurus sarcophagus . 
