Species and Distribution
Edmontosaurus is currently regarded as having two valid species: type species E. regalis, and E. annectens. E. regalis is known only from the Horseshoe Canyon Formation of Alberta, dating from the late Campanian stage of the late Cretaceous period. At least a dozen individuals are known, including seven skulls with associated postcrania, and five to seven other skulls. The species formerly known as Thespesius edmontoni or Anatosaurus edmontoni represents immature individuals. Trachodon atavus and Agathaumas milo are potential synonyms.
E. annectens is known from the Frenchman Formation of Saskatchewan, the Hell Creek Formation of Montana, and the Lance Formation of South Dakota and Wyoming. It is limited to late Maastrichtian rocks, and is represented by at least twenty skulls, some with postcranial remains. One author, Kraig Derstler, has described E. annectens as "perhaps the most perfectly-known dinosaur to date ." Anatosaurus copei and E. saskatchewanensis are now thought to be growth stages of E. annectens: A. copei as adults, and E. saskatchewanensis as juveniles. Trachodon longiceps may be a synonym of E. annectens as well. Anatosaurus edmontoni has sometimes been assigned to E. annectens, but this does not appear to be the case.
E. annectens differed from E. regalis by having a longer, lower, less robust skull. Although Brett-Surman regarded E. regalis and E. annectens as potentially representing males and females of the same species, all E. regalis specimens come from older formations than E. annectens specimens.
Additionally, there are many Edmontosaurus fossils that have not been identified to species. Remains that have not been assigned to a particular species (identified as E. sp.) may extend the range of the genus as far as the Prince Creek Formation of Alaska and the Javelina Formation of Texas.
Read more about this topic: Edmontosaurus
Famous quotes containing the words species and, species and/or distribution:
“Prostitution is the most hideous of the afflictions produced by the unequal distribution of the world’s goods; this infamy stigmatizes the human species and bears witness against the social organization far more than does crime.”
—Flora Tristan (1803–1844)
“If we consider the superiority of the human species, the size of its brain, its powers of thinking, language and organization, we can say this: were there the slightest possibility that another rival or superior species might appear, on earth or elsewhere, man would use every means at his disposal to destroy it.”
—Jean Baudrillard (b. 1929)
“There is the illusion of time, which is very deep; who has disposed of it? Mor come to the conviction that what seems the succession of thought is only the distribution of wholes into causal series.”
—Ralph Waldo Emerson (1803–1882)