Edmontosaurus
Edmontosaurus, with the second species often colloquially and historically known as Anatosaurus or Anatotitan, is a genus of hadrosaurid (duck-billed) dinosaur. It contains two known species: Edmontosaurus regalis and Edmontosaurus annectens. Fossils of E. regalis have been found in rocks of western North America that date from the late Campanian age of the Cretaceous period 73 million years ago, while those of E. annectens were found in the same geographic region from rocks dated to the end of the Maastrichtian age, 66 million years ago. Edmontosaurus was one of the last non-avian dinosaurs to ever exist, and lived alongside dinosaurs like Triceratops, Tyrannosaurus, Ankylosaurus, and Pachycephalosaurus shortly before the Cretaceous–Paleogene extinction event. Edmontosaurus included two of the largest hadrosaurid species, with E. annectens measuring up to 12 metres (39 ft) in length and weighing around 5.6 metric tons in average asymptotic body mass, although some individuals would have been much larger. Several well-preserved specimens are known that include numerous bones, as well as extensive skin impressions and possible gut contents. Edmontosaurus is classified as a genus of saurolophine hadrosaurid, a member of the group of hadrosaurids that lacked large, hollow crests and instead had smaller, solid crests or fleshy combs. The first fossils named Edmontosaurus were discovered in southern Alberta, in the Horseshoe Canyon Formation. The type species, E. regalis, was named by Lawrence Lambe in 1917, although several other species that are now classified in Edmontosaurus were named earlier. The best known of these is E. annectens, named by Othniel Charles Marsh in 1892. This species was originally as a species of Claosaurus, known for many years as a species of Trachodon, and later known as Anatosaurus annectens. Anatosaurus, Anatotitan, and probably Ugrunaaluk are now generally regarded as synonyms of Edmontosaurus. Edmontosaurus was widely distributed across western North America, ranging from Colorado to the northern slopes of Alaska. The distribution of Edmontosaurus fossils suggests that it preferred coasts and coastal plains. It was a herbivore that could move on both two legs and four. Because it is known from several bone beds, Edmontosaurus is thought to have lived in groups and may have been migratory as well. The wealth of fossils has allowed researchers to study its paleobiology in detail, including its brain, how it may have fed, and its injuries and pathologies, such as evidence for tyrannosaur attacks on a few specimens.
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