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/or distribution:
“Can it then be doubted, but that God, who is infinitely fine Spirit, and withal intelligent, can make and change all species and kind of body as he pleaseth? But I dare not say, that this is the way by which God Almighty worketh, because it is past my apprehension: yet it serves very well to demonstrate, that the omnipotence of God implieth no contradiction.”
—Thomas Hobbes (1579–1688)
“In this distribution of functions, the scholar is the delegated intellect. In the right state, he is, Man Thinking. In the degenerate state, when the victim of society, he tends to become a mere thinker, or, still worse, the parrot of other men’s thinking.”
—Ralph Waldo Emerson (1803–1882)