 Matthew and Brown also described a fifth skeleton ( AMNH <unk> ) , which Charles H. Sternberg had collected in 1917 and sold to their museum . It was smaller than other Gorgosaurus specimens , with a lower , lighter skull and more elongate limb proportions . Many sutures between bones were unfused in this specimen as well . Matthew and Brown noted that these features were characteristic of juvenile tyrannosaurids , but still described it as the holotype of a new species , G. sternbergi . Today 's paleontologists regard this specimen as a juvenile G. libratus . Dozens of other specimens have been excavated from the Dinosaur Park Formation and are housed in museums across the United States and Canada . G. libratus is the best @-@ represented tyrannosaurid in the fossil record , known from a virtually complete growth series . 
