described a fifth skeleton (AMNH 5664), 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. In 1856, Joseph Leidy described two tyrannosaurid premaxillary teeth from Montana. Although there was no indication of what the animal looked like, the teeth were large and robust, and Leidy gave them the name Deinodon. Matthew and Brown commented in 1922 that these teeth were indistinguishable from those of Gorgosaurus, but in the absence of skeletal remains of Deinodon, opted not to unequivocally synonymize the two genera, provisionally naming a ?Deinodon libratus. Although Deinodon teeth are very similar to those of Gorgosaurus, tyrannosaurid teeth are extremely uniform, so it cannot be said for certain which animal they belonged to. Deinodon is usually regarded as a nomen dubium today. Additional likely synonyms of G. libratus and/or D. horridus include Laelaps falculus, Laelaps hazenianus, Laelaps incrassatus, and Dryptosaurus kenabekides. Several tyrannosaurid skeletons from the Two Medicine Formation and Judith River Formation of Montana probably belong to Gorgosaurus, although it remains uncertain whether they belong to G. libratus or a new species. One specimen from Montana (TCMI 2001.89.1), housed in the Children's Museum of Indianapolis, shows evidence of severe pathologies, including healed leg, rib, and vertebral fractures, osteomyelitis (infection) at the tip of the lower jaw resulting in permanent tooth loss, and possibly a brain tumor. Formerly assigned species Several species were incorrectly assigned to Gorgosaurus in the 20th century. A complete skull of a small tyrannosaurid (CMNH 7541), found in the younger, late Maastrichtian-age Hell Creek Formation of Montana, was named Gorgosaurus lancensis by Charles Whitney Gilmore in 1946. This specimen was renamed Nanotyrannus by Bob Bakker and colleagues in 1988. Currently, many paleontologists regard Nanotyrannus as a juvenile Tyrannosaurus rex. Similarly, Evgeny Maleev created the names Gorgosaurus lancinator and