Edmontonian

For the demonym of people from Edmonton, see List of people from Edmonton.

The Edmontonian was a North American faunal epoch occurring during the Late Cretaceous, lasting from approximately 70 to 68 million years ago.

Paleobiogeography

Main article: Dinosaur paleobiogeography

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]