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

Paleobiogeography

In southern North America, little changed in the transition from the

Judithian The Judithian was a North American faunal stage lasting from 83.5 to 70.6 million years ago. It overlaps with the Campanian global stage. Fauna Dinosaur faunas of the Judithian age may represent the peak of dinosaur evolution in North America. H ...

to the Edmontonian. However, the northern biome experienced a general trend in reduction of

centrosaurine Centrosaurinae (from the Greek, meaning "pointed lizards") is a subfamily of ceratopsid dinosaurs, a group of large quadrupedal ornithischians. Centrosaurine fossil remains are known primarily from the northern region of Laramidia (modern day ...

s, with leaving ''

Pachyrhinosaurus ''Pachyrhinosaurus'' (meaning in Greek "thick-nosed lizard", from ' (), thick; ' (), nose; and (), lizard) is an extinct genus of centrosaurine ceratopsid dinosaur from the Late Cretaceous period of North America. The first examples were disco ...

'' as one of the few surviving species. Likewise among

lambeosaur Lambeosaurinae is a group of crested hadrosaurid dinosaurs. Classification Lambeosaurines have been traditionally split into the tribes or clades Parasaurolophini (''Parasaurolophus'', ''Charonosaurus'', others (?).) and Lambeosaurini (''Cory ...

s, only the single genus ''

Hypacrosaurus ''Hypacrosaurus'' (meaning "near the highest lizard"

reek υπο-, ''hypo-'' = less + ακρος, ''akros'', high Reek may refer to: Places * Reek, Netherlands, a village in the Dutch province of North Brabant * Croagh Patrick, a mountain in the west of Ireland nicknamed "The Reek" People * Nikolai Reek (1890-1942), Estonian military commander * Salme Reek ( ...

because it was almost but not quite as large as ''Tyrannosaurus'') was a genus of hadrosaurid, duckbill dinosaur similar in app ...

'' remained. Inland faunas of the age are distinguished by a ''

Saurolophus ''Saurolophus'' (; meaning "lizard crest") is a genus of large hadrosaurid dinosaur from the Late Cretaceous period of Asia and North America, that lived in what is now the Horseshoe Canyon and Nemegt formations about 70 million to 68 millio ...

''-''

Anchiceratops ''Anchiceratops'' ( ) is an extinct genus of chasmosaurinae, chasmosaurine ceratopsid dinosaur that lived approximately 72 to 71 million years ago during the latter part of the Cretaceous Period (geology), Period in what is now Alberta, Canada. ' ...

'' association while more coastal areas were characterized by ''Pachyrhinosaurus'' and ''

Edmontosaurus ''Edmontosaurus'' ( ) (meaning "lizard from Edmonton") is a genus of hadrosaurid (duck-billed) dinosaur. It contains two known species: '' Edmontosaurus regalis'' and '' Edmontosaurus annectens''. Fossils of ''E. regalis'' have been found in ro ...

''. ''Pachyrhinosaurus'' occurred as far north as Alaska. "Archaic" elements such as

hypsilophodont Hypsilophodontidae (or Hypsilophodontia) is a traditionally used family of ornithopod dinosaurs, generally considered invalid today. It historically included many small bodied bipedal neornithischian taxa from around the world, and spanning from ...

s like ''

Parksosaurus ''Parksosaurus'' (meaning " William Parks's lizard") is a genus of neornithischian dinosaur from the early Maastrichtian-age Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada. It is based on most of a partially articulated skeleton ...

'' and the "(re)appearance" of basal neoceratopsians like ''

Montanoceratops ''Montanoceratops'' is an extinct genus of small ceratopsian dinosaur that lived approximately 70 million years ago during the latter part of the Cretaceous Period in what is now Montana and Alberta. ''Montanoceratops'' was a small sized, mode ...

'' begin characterizing inland faunas. Paleontologist Thomas M. Lehman described the Edmontonian ''

Arrhinoceratops ''Arrhinoceratops'' (meaning "no nose-horn face", derived from the Ancient Greek "a-/α-" "no", rhis/ῥίς "nose" "keras/κέρας" "horn", "-ops/ὤψ" "face") is a genus of herbivorous ceratopsian dinosaur. The name was coined as its origina ...

'' as a likely ancestor for the

Lancian The Lancian was a North American faunal stage of the Late Cretaceous. It was the final stage of the Cretaceous period in North America, lasting from approximately 70.6 to 66 million years ago. Geology Terrestrial sedimentary strata from the Judit ...

Triceratops ''Triceratops'' ( ; ) is a genus of herbivorous chasmosaurine ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous period, about 68 million years ago in what is now North America. It is ...

''. Ecological disturbance brought them to an end during the Edmontonian. Relative sea levels fell very rapidly due to the

Laramide orogeny The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the o ...

. 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

protoceratopsid Protoceratopsidae is a family of basal (primitive) ceratopsians from the Late Cretaceous period. Although ceratopsians have been found all over the world, protoceratopsids are only definitively known from Cretaceous strata in Asia, with most spec ...

s and

sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their ...

s began expanding into lower altitude areas as sea-levels fell.

Footnotes

References

* * *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. * Reprinted in {{cite book, last1=Halstead, first1=L.B., title=Dinosaur studies : commemorating the 150th anniversary of Richard Owen's Dinosauria., date=1991, publisher=Gordon and Breach, location=Philadelphia, isbn=9782881248337 Cretaceous geochronology Maastrichtian Stage of North America