are animals that dominated terrestrial
environments for more than 160 million years, first appearing approximately 230 million years
ago. They were extremely varied, abundant and have been found preserved on all seven modern continents. At the end of the Cretaceous period
, approximately 66 million years ago, a catastrophic extinction event
ended the dinosaurs' dominance on land. However, since birds are theropods
the clade dinosauria still survives in great diversity and abundance. The term "dinosaur" is sometimes used mistakenly to describe other prehistoric animals, such as the synapsid Dimetrodon
, or reptiles like pterosaurs
. Since the first dinosaur fossils
were recognized in the nineteenth century, mounted dinosaur skeletons have become major attractions at museums
around the world and have amassed a large fan base among children and adults alike. They have been featured in best-selling books
such as Jurassic Park
, and new discoveries are regularly covered by the media
Gorgosaurus (meaning 'fierce lizard') is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, between about 77 and 74 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 a metric ton 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. An apex predator, it was at the top of the food chain, preying upon abundant ceratopsids and hadrosaurs. In some areas, Gorgosaurus coexisted with another tyrannosaurid, Daspletosaurus. Though 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. (see more...)