Edmontosaurus annectens
Edmontosaurus annectens, often colloquially and historically known as Anatosaurus, 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. 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 in length and 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. References predating the 1980s typically use Anatosaurus, Claosaurus, Diclonius, Thespesius, or Trachodon for E. annectens fossils, depending on the author and date.Cope's ''Diclonius mirabilis''
The history of E. annectens predates the naming of both the genus Edmontosaurus and the species annectens. The first quality specimen, the former holotype of Anatosaurus copei, was a complete skull and most of a skeleton collected in 1882 by Dr. J. L. Wortman and R. S. Hill for American paleontologist Edward Drinker Cope. This specimen, found in Hell Creek Formation rocks, came from northeast of the Black Hills of South Dakota, and originally had extensive skin impressions. It was missing most of its pelvis and part of its torso due to a stream cutting through it. The bill had impressions of a horn-like sheath with a tooth-like series of interlocking points on the upper and lower jaws. When describing this specimen, AMNH 5730, Cope assigned it to the species Diclonius mirabilis. This species name was created by combining Diclonius, a hadrosaurid genus Cope had named earlier from teeth, with Trachodon mirabilis, an older name based on teeth that was published by Joseph Leidy. Cope believed that Leidy had failed to properly characterize the genus Trachodon and later abandoned its use, so he assigned the old species to his newer genus. Leidy had come to recognize that his Trachodon was based on the remains of multiple kinds of dinosaurs, and although he had made some attempts to revise the genus, he had not yet made any formal declaration of his intentions.Cope's description promoted hadrosaurids as amphibious animals, contributing to this long-time image. His reasoning was that the teeth of the lower jaw were weakly connected to the bone, and liable to break off if used to eat terrestrial food; he described the beak as weak, too. However, aside from misidentifying several of the skull bones, by chance, the lower jaws were missing the walls supporting the teeth from the inside, and the teeth were actually very well-supported. Cope intended to describe the skeleton and skull, but his promised paper never appeared. It was purchased for the American Museum of Natural History in 1899, where it acquired its present designation: AMNH 5730.
File:Edmontosaurus annectens, by Charles R. Knight.jpg|thumb|Outdated 1909 life restoration of Trachodon by Charles R. Knight, based on the two specimens mounted in 1908 at the AMNH, New York.
Several years after Cope's description, his arch-rival, Othniel Charles Marsh, published a paper on a sizable lower jaw recovered by John Bell Hatcher in 1889 from the Lance Formation rocks in Niobrara County, Wyoming. Marsh named this partial jaw Trachodon longiceps, and it is cataloged as YPM 616. As noted by Lull and Wright, this long, slender partial jaw shares with Cope's specimen a prominent ridge running on its side. However, it is much larger: Cope's specimen had a dentary that is long, whereas Marsh's dentary is estimated at long.
A second mostly complete skeleton, AMNH 5886, was found in 1904 in the Hell Creek Formation rocks at Crooked Creek in central Montana by a local rancher named Oscar Hunter. Upon finding the partially exposed specimen, he and a companion argued about whether or not the remains were recent or fossil. Hunter demonstrated that they were brittle and thus stone by kicking the tops off the vertebrae, an act later lamented by the eventual collector Barnum Brown. Another cowboy, Alfred Sensiba, bought the specimen from Hunter for a pistol and later sold it to Brown, who excavated it for the American Museum of Natural History in 1906. This specimen had a nearly complete vertebral column, permitting the restoration of Cope's specimen. In 1908, these two specimens were mounted side by side in the American Museum of Natural History under the name Trachodon mirabilis. Cope's specimen is positioned on all fours with its head down, as if feeding, because it has the better skull, while Brown's specimen, with a less perfect skull, is posed bipedally with the head less accessible. Henry Fairfield Osborn described the tableau as representing the two animals feeding alongside a marsh, the standing individual having been startled by the approach of a Tyrannosaurus. Impressions of appropriate plant remains and shells based on associated fossils were included on the base of the group, including ginkgo leaves, Sequoia cones, and horsetail rushes.
Marsh's ''Claosaurus annectens''
The species now known as Edmontosaurus annectens was named in 1892 as Claosaurus annectens by Othniel Charles Marsh. This species is based on USNM 2414, a partial skull-roof and skeleton, with a second skull and skeleton, YPM 2182, being designated as the paratype. Both were collected in 1891 by John Bell Hatcher, from the late Maastrichtian-age Upper Cretaceous Lance Formation of Niobrara County, Wyoming. This species has some historical footnotes attached, as it is among the first dinosaurs to receive a skeletal restoration, and is the first hadrosaurid so restored. YPM 2182 and UNSM 2414 are, respectively, the first and second essentially complete mounted dinosaur skeletons in the United States. YPM 2182 was put on display in 1901, and USNM 2414 was put on display in 1904.In the first decade of the twentieth century, two additional important specimens of C. annectens were recovered. The first, the "Trachodon mummy," AMNH 5060, was discovered in 1908 by Charles Hazelius Sternberg and his sons in the Lance Formation rocks near Lusk, Wyoming. Sternberg was working for the British Museum of Natural History, but Henry Fairfield Osborn of the American Museum of Natural History was able to purchase the specimen for $2,000. The Sternbergs recovered a second similar specimen from the same area in 1910. It was not as well-preserved, but also found with skin impressions. They sold this specimen, SM 4036, to the Senckenberg Museum in Germany.
Canadian discoveries
Edmontosaurus itself was coined in 1917 by Lawrence Lambe for two partial skeletons found in the Horseshoe Canyon Formation, along the Red Deer River of southern Alberta. The Horseshoe Canyon Formation is older than the rocks in which Claosaurus annectens was found. Lambe found that his new dinosaur compared best to Cope's Diclonius mirabilis.In 1926, Charles Mortram Sternberg named Thespesius saskatchewanensis for NMC 8509, a skull and partial skeleton from the Wood Mountain plateau of southern Saskatchewan. He had collected this specimen in 1921 from rocks that were assigned to the Lance Formation, now the Frenchman Formation. NMC 8509 included an almost complete skull, numerous vertebrae, partial shoulder and hip girdles, and partial back legs, representing the first substantial dinosaur specimen recovered from Saskatchewan. Sternberg opted to assign it to Thespesius because that was the only hadrosaurid genus known from the Lance Formation at the time. At the time, T. saskatchewanensis was unusual because of its small size, estimated at in length.