Edmontonian
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The Edmontonian was a North American faunal epoch occurring during the Late Cretaceous, lasting from approximately 70 to 68 million years ago.
Paleobiogeography
[edit | edit source]In southern North America, little changed in the transition from the Judithian to the Edmontonian.[1] However, the northern biome experienced a general trend in reduction of centrosaurines, with leaving Pachyrhinosaurus as one of the few surviving species.[2] Likewise among lambeosaurs, only the single genus Hypacrosaurus remained.[3] Inland faunas of the age are distinguished by a Saurolophus-Anchiceratops association while more coastal areas were characterized by Pachyrhinosaurus and Edmontosaurus.[3] Pachyrhinosaurus occurred as far north as Alaska.[3] "Archaic" elements such as hypsilophodonts like Parksosaurus and the "(re)appearance" of basal neoceratopsians like Montanoceratops begin characterizing inland faunas.[3] Paleontologist Thomas M. Lehman described the Edmontonian Arrhinoceratops as a likely ancestor for the Lancian Triceratops.[3]
Ecological disturbance brought them to an end during the Edmontonian.[4] Relative sea levels fell very rapidly due to the Laramide orogeny.[4] Opportunistic generalist herbivores filled the vacated niches that were once filled by a diverse number of specialist forms.[4] The newly formed ecosystems tended to be dominated by a single herbivorous species each.[4] The new dominant herbivores were usually less ornamented and probably represent "survivors from indigenous lineages" rather than immigrants from other areas.[4] Gradually however "relict" dinosaurs such as protoceratopsids and sauropods began expanding into lower altitude areas as sea-levels fell.[4]
Footnotes
[edit | edit source]References
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- Lehman, T. M., 2001, Late Cretaceous dinosaur provinciality: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, pp. 310–328.
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