page_title: Gorgosaurus
section_title: Discovery and naming
hierarchical_section_title: Gorgosaurus / Discovery and naming
caption_attribution_description: English: Skeleton of Gorgosaurus libratus, assigned to Deinodon. Français&#160;: Squelette de Gorgosaurus libratus.
context_page_description: Gorgosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, between about 76.6 and 75.1 million years ago. Fossil remains have been found in the Canadian province of Alberta and possibly the U.S. state of Montana. Paleontologists recognize only the type species, G. libratus, although other species have been erroneously referred to the genus.
  Like most known tyrannosaurids, Gorgosaurus was a bipedal predator weighing more than two metric tons as an adult; dozens of large, sharp teeth lined its jaws, while its two-fingered forelimbs were comparatively small. Gorgosaurus was most closely related to Albertosaurus, and more distantly related to the larger Tyrannosaurus. Gorgosaurus and Albertosaurus are extremely similar, distinguished mainly by subtle differences in the teeth and skull bones. Some experts consider G. libratus to be a species of Albertosaurus; this would make Gorgosaurus a junior synonym of that genus.
  Gorgosaurus lived in a lush floodplain environment along the edge of an inland sea. It was an apex predator, preying upon abundant ceratopsids and hadrosaurs.
context_section_description: Gorgosaurus libratus was first described by Lawrence Lambe in 1914. Its name is derived from the Greek γοργος/gorgos ("fierce" or "terrible") and σαυρος/saurus ("lizard"). The type species is G. libratus; the specific epithet "balanced" is the past participle of the Latin verb librare, meaning "to balance".
  The holotype of Gorgosaurus libratus (NMC 2120) is a nearly complete skeleton associated with a skull, discovered in 1913 by Charles M. Sternberg. This specimen was the first tyrannosaurid found with a complete hand. It was found in the Dinosaur Park Formation of Alberta and is housed in the Canadian Museum of Nature in Ottawa. Prospectors from the American Museum of Natural History in New York City were active along the Red Deer River in Alberta at the same time, collecting hundreds of spectacular dinosaur specimens, including four complete G. libratus skulls, three of which were associated with skeletons. Matthew and Brown described four of these specimens in 1923.
  Matthew and Brown also 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.
caption: Type specimen of Gorgosaurus sternbergi (AMNH 5664), now recognized as a juvenile Gorgosaurus libratus
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