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Edmontonian
The Edmontonian was a North American faunal stage occurring during the Late Cretaceous.
==Paleobiogeography==
In southern North America, little changed in the transition from the Judithian to the Edmontonian.〔 However, the northern biome experienced a general trend in reduction of centrosaurines, with only ''Pachyrhinosaurus'' surviving.〔 Likewise among lambeosaurs, only the single genus ''Hypacrosaurus'' remains.〔 Inland faunas of the age are distinguished by a ''Saurolophus''-''Anchiceratops'' association while more coastal areas were characterized by ''Pachyrhinosaurus'' and ''Edmontosaurus''.〔 ''Pachyrhinosaurus'' occurred as far north as Alaska.〔 "Archaic" elements such as hypsilophodonts like ''Parksosaurus'' and the "(re)appearance" of basal neoceratopsians like ''Montanoceratops'' begin characterizing inland faunas.〔 Paleontologist Thomas M. Lehman described the Edmontonian ''Arrhinoceratops'' as a likely ancestor for the Lancian ''Triceratops''.〔
Ecological disturbance brought them to an end during the Edmontonian.〔 Relative sea levels fell very rapidly due to the Laramide orogeny.〔 Opportunistic generalist herbivores filled the vacated niches that were once filled by a diverse number of specialist forms.〔 The newly formed ecosystems tended to be dominated by a single herbivorous species each.〔 The new dominant herbivores were usually less ornamented and probably represent "survivors from indigenous lineages" rather than immigrants from other areas.〔 Gradually however "relict" dinosaurs such as protoceratopsids and sauropods began expanding into lower altitude areas as sea-levels fell.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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