Dinosaur paleobiogeography
"[1] Provincialism was even present during the turbulent faunal turnover of the Maastrichtian stage, when the Laramide Orogeny triggered "the most dramatic event that affected Late Cretaceous dinosaur communities in North America prior to their extinction.
"[1] This turnover event saw specialized and highly ornamented centrosaurines and lambeosaurines be replaced by more primitive upland dinosaurs in the south while northern biomes became dominated by Triceratops with a greatly reduced hadrosaur community.
[2] Many dinosaur species in North America during the Late Cretaceous had "remarkably small geographic ranges" despite their large body size and high mobility.
"[3] He notes that Corythosaurus and Centrosaurus haven't been discovered outside of southern Alberta even though they are the most abundant Judithian dinosaurs in the region.
[4] Only the rarer species among modern mammal communities would be able to distinguish different latitudinal zones, and some of these taxa are likely too rare to fossilize.
[4] Restrictions in herbivorous dinosaur distribution may be due to foliage preferences, narrow tolerance for variation in climate or other environmental factors.
[7] There may be parallels to this phenomenon in Cretaceous ecosystems, for instance, Pachyrhinosaurus is found in both Alaska and upland environments in southern Alberta.
[8] Earlier research had found that lambeosaurines are less common in contemporary Montanan strata and with different centrosaurs as Monoclonius taking the place of Centrosaurus.
[8] Farther south was characterized by lower taxonomic diversity in communities where lambeosaurines were less common and centrosaurs were completely lacking.
[11] "Archaic" elements such as hypilophodonts like Parksosaurus and the "(re)appearance" of basal neoceratopsians like Montanoceratops begin characterizing inland faunas.
The rock types within the formations are primarily coal beds, but also include sandstone, siltstone, mudstone, and shale.
The Bisti Bed of the Hunter Wash Member is made up completely of sandstone, which marks the border between the Kirtland and Fruitland formations.
It was first named by Robert M. Sullivan and Spencer G. Lucas in 2003 and found by their original study to date from 74.9 to 72 million years ago.
The species include the dinosaurians Pentaceratops sternbergii, Parasaurolophus cyrtocristatus, and Kritosaurus navajovius,[12] with the only non-dinosaurian being Melvius chauliodous, a fish taxon.
In 1975, Russell identified five Late Cretaceous land-vertebrate ages, the Paluxian, Aquilan, Judithian, Edmontonian, and Lancian, based on mammal assemblages.
[17] In the south the transition to the Lancian is even more dramatic, which Lehman describes as "the abrupt reemergence of a fauna with a superficially "Jurassic" aspect.
"[19] The rapid expansion of land and drying of inland climate accompanying a drop in sea level could explain some of the environmental changes occurring Late Cretaceous western North America.
[21] If the geographic range of some dinosaur species were truly as limited as the fossil record suggests, then a rapid rise and in sea level could cause intense pressure even the event was local.
[21] Inhabitants of upland environment are more likely to be endemic than coastal species, and tend to have less of an ability to cross bodies of water.
[21] Quetzalcoatlus also had precursors in North America and its apparent rise to widespreadness may represent the expansion of its preferred habitat rather than an immigration event.
[21] Early Cretaceous deposits in North America reveal that basal neoceratopsian were already present on the continent before their apparent reemergence in the Lancian, so an immigration event from Asia is unnecessary to explain their appearance.
[22] Lehman described the evidence for immigration as a driving force in Lancian dinosaur faunal turnovers as "not particularly compelling.
"[21] The faunal turnover may be explained by the descent of more primitive forms existing in upland refugia characterized by conifer-dominated flora into areas that were formerly coastal lowlands as the seas retreated and conditions became more arid.
[23] The decline of mammal diversity in Western North America from the Miocene to present primarily effected large herbivores and occurred over roughly the same length of time as the Late Cretaceous changes, and so may be parallel.
[25] A dispersal event near the Cenomanian preceded the development of endemic northern and southern biomes in Western North America during the Late Cretaceous.
[2] Environments with highly favorable conditions led to diverse ecosystems populated by ornate herbivores with complex social interactions.
[2] Gradually however "relict" dinosaurs such as protoceratopsids and sauropods began expanding into lower altitude areas as sea-levels fell.
[2] At the very least, Lehman argues, the altitudinal life zones would shift, and a change in the distribution of vegetation utilized by herbivorous dinosaurs would have probably resulted.
