Paleobiogeography

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

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...

 to the Edmontonian. However, the northern biome experienced a general trend in reduction of centrosaurines, with only Pachyrhinosaurus

Pachyrhinosaurus

Pachyrhinosaurus is a genus of ceratopsid dinosaurs from the Late Cretaceous period of North America. The first examples were discovered by Charles M. Sternberg in Alberta, Canada, in 1946, and named in 1950. Over a dozen partial skulls and a large assortment of other fossils from various species...

surviving. Likewise among lambeosaurs, only the single genus Hypacrosaurus

Hypacrosaurus

Hypacrosaurus was a genus of duckbill dinosaur similar in appearance to Corythosaurus. Like Corythosaurus, it had a tall, hollow rounded crest, although not as large and straight...

remains. Inland faunas of the age are distinguished by a Saurolophus

Saurolophus

Saurolophus is a genus of large hadrosaurine duckbill that lived about 69.5-68.5 million years ago, in the Late Cretaceous of North America and Asia; it is one of the few genera of dinosaurs known from multiple continents. It is distinguished by a spike-like crest which projects up and back...

-Anchiceratops

Anchiceratops

Anchiceratops is a genus of chasmosaurine ceratopsid dinosaur from the Late Cretaceous Period of western North America. Like other ceratopsids, it was a quadrupedal herbivore with three horns on its face, a parrot-like beak, and a long frill extending from the back of its head. The two horns above...

association while more coastal areas were characterized by Pachyrhinosaurus and Edmontosaurus

Edmontosaurus

Edmontosaurus is a genus of crestless hadrosaurid dinosaur. It contains two species: Edmontosaurus regalis and Edmontosaurus annectens. Fossils of E. regalis have been found in rocks of western North America that date from the late Campanian stage of the Cretaceous Period 73 million years ago,...

. Pachyrhinosaurus occurred as far north as Alaska. "Archaic" elements such as hypilophodonts like Parksosaurus

Parksosaurus

Parksosaurus was a genus of hypsilophodont ornithopod 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 partial skull, showing it to have been a small, bipedal, herbivorous dinosaur...

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

Montanoceratops

Montanoceratops was a genus of small ceratopsian dinosaur. It lived during the early Maastrichtian of the late Cretaceous Period...

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

Arrhinoceratops

Arrhinoceratops is a genus of ceratopsian dinosaur. The name was coined as its original describer concluded it had no nose-horn, however further analysis revealed this not to be the case...

as a likely ancestor for the Lancian

Lancian

-Geology:Terrestrial sedimentary strata from the Judithian to the Lancian are generally regressive through-out the entire sequence, so the preserved changes in fossil communities represent not only phylogenetic changes but ecological zones from the submontane habitats to near-sea level coastal...

 Triceratops

Triceratops

Triceratops is a genus of herbivorous ceratopsid dinosaur which lived during the late Maastrichtian stage of the Late Cretaceous Period, around 68 to 65 million years ago in what is now North America. It was one of the last dinosaur genera to appear before the great Cretaceous–Paleogene...

.

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.