Edmontosaurus annectens

Edmontosaurus annectens (meaning "connected lizard from Edmonton"), often colloquially and historically known as Anatotitan (meaning "duck titan"), is a species of flat-headed saurolophine hadrosaurid dinosaur from the late Maastrichtian age at the very end of the Cretaceous period, in what is now western North America. Remains of E. annectens have been preserved in the Frenchman, Hell Creek, and Lance Formations. All of these formations are dated to the late Maastrichtian age of the Late Cretaceous period, which represents the last three million years before the extinction of the non-avian dinosaurs (between 68 and 66 million years ago). E. annectens is also found in the Laramie Formation, and magnetostratigraphy suggests an age of 69–68 Ma for the Laramie Formation.

Edmontosaurus annectens is known from numerous specimens, including at least twenty partial-to-complete skulls, discovered in the U.S. states of Montana, South Dakota, North Dakota, Wyoming, and Colorado, as well as the Canadian province of Saskatchewan. It had an extremely long and low skull, and was quite a large animal, growing up to approximately 12 metres (39 ft) in length and 5.6 metric tons (6.2 short tons) in average asymptotic body mass, although it could have been even larger. E. annectens exhibits one of the most striking examples of the "duckbill" snout that is common to hadrosaurs. It has a long taxonomic history, and specimens have at times been classified as Diclonius, Trachodon, Hadrosaurus, Claosaurus, Thespesius, Anatosaurus, and Anatotitan before all being grouped together in Edmontosaurus.

Discovery and history

E. annectens has a complicated taxonomic history, with various specimens having been classified in a variety of genera. Its history involves Anatosaurus, Anatotitan, Claosaurus, Diclonius, Hadrosaurus, Thespesius, and Trachodon, as well as Edmontosaurus.