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Gorgosaurus libratus

"Dreadful Lizard"

Gorgosaurus (/ˌɡɔːrɡəˈsɔːrəs/ GOR-gə-SOR-əs; lit. 'dreadful lizard') is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period (Campanian), between about 76.5 and 75 million years ago. Fossil remains have been found in the Canadian province of Alberta and 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 large bipedal predator, measuring 8–9 metres (26–30 ft) in length and 2–3 metric tons (2.2–3.3 short tons) in body mass. 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. In some areas, Gorgosaurus coexisted with another tyrannosaurid, Daspletosaurus. Although these animals were roughly the same size, there is some evidence of niche differentiation between the two. Gorgosaurus is the best-represented tyrannosaurid in the fossil record, known from dozens of specimens. These plentiful remains have allowed scientists to investigate its ontogeny, life history and other aspects of its biology.