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.[1] However, the northern biome experienced a general trend in reduction of centrosaurines, with only Pachyrhinosaurus surviving.[2] Likewise among lambeosaurs, only the single genus Hypacrosaurus remains.[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

  1. ↑ "Edmontonian Transition," Lehman (2001); page 315.
  2. ↑ "Edmontonian Transition," Lehman (2001); pages 315-317.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 "Edmontonian Transition," Lehman (2001); page 317.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 "Conclusions," Lehman (2001); page 324.

References