Throughout the last two decades roughly, palaeontologists studying the Late Cretaceous fauna of North America can see an incredible selection of Ornithischian dinosaurs in strata laid down between 80 million and 70 million years ago. Numerous horned dinosaurs such as Vagaceratops, Utahceratops and Kosmoceratops along with several new genera of Hadrosaurs (duck-billed dinosaurs) have been described from western North America. Most palaeontologists have been dedicated to mapping the faunal distribution and studying the myriad of new plant-eating dinosaur species which were found, but several scientists are actually embracing the mystery of why so many several types of dinosaur evolved in this part of the world during the last few million years of the Cretaceous.
Diversity Explanation Is based on the Geology
For one team of researchers based at Ohio University, the explanation concerning dinosaur diversity lies in the geology. The rise of the Rocky Mountain range and the looks and then disappearance of a huge, inland seaway that split North America into some islands, may have been the catalysts for an explosion in megafauna diversity. The investigation team from the University’s Heritage College of Osteopathic Medicine experienced their paper published in the on line scientific journal PloS One (public library of science). what dinosaur has 500 teeth They state that the rapid changing geology led to populations of animals being isolated that might explain the patterns of evolution, migration and rapid dinosaur diversification.
Terry Gates, the lead author of the paper and a post-doctoral student at the University commented that over the past few decades palaeontologists have grown to be increasingly aware of the huge array of several types of plant-eating dinosaur that roamed what was to end up being the United States and Canada. However, immediately, before the Cretaceous mass extinction, there were only a few dominant dinosaur species across the whole continent. This phenonmenon has yet to be fully explained.
Examining the Geological Record of North America
The investigation team attempt to examine the geological record of what was to end up being the continent of North America, concentrating on the United States and Canada. Throughout the Campanian faunal stage of the Cretaceous, a amount of time in the Earth’s history that roughly relates to 83 million years ago to 74 million years ago there was extensive plate tectonic activity that led to mountain ranges being pushed up and the sinking of a lot of the continental landmass under an inland sea (known whilst the Western Interior Seaway). At its most extensive, this seaway covered a lot of North America from Canada to the Gulf of Mexico.
In the later Maastrichtian faunal stage, that lasted from 74 million years ago up before mass extinction event 65 million years ago, there was less extensive plate activity. This coincided with a decline in the amount of genera of dinosaur known from the fossil record. Palaeontologists have interpreted this as evidence as a fall in the amount of dinosaur species living in North America towards ab muscles end of the Cretaceous – dinosaur genera became less diverse.
Mountain Building Isolating Populations
Geologists have calculated that throughout the Early Cretaceous there was a substantial level of geological activity in the western United States. Numerous processes involving subduction, the movement of ocean crust into the Earth’s mantle occurred along what was to end up being the western coast of North America. These immense geological forces caused the western part of the Americas to be lifted up and this led to the formation of a huge mountain range that extended from Alberta (Canada) in a south-western direction to as far south whilst the southern United States. The region to the east of this newly formed mountain range (the Sevier Mountains), flexed downwards and this coincided with a rise in global sea levels, flooding a lot of the continent and splitting what land remained above sea level into some large islands. This sea (Western Interior Seaway), teemed with life and the marine deposits left out in places as far apart as Alberta and Kansas have provided palaeontologists by having an amazing selection of marine reptile fossils to study – Dolichorhynchops, Elasmosaurs and huge Mosasaurs such as Tylosaurus.
The Ohio based research team have dedicated to the dinosaur fossils which were within association with the islands. At its most extensive, the Western Interior Seaway split the North American land mass into three large islands. These islands each had a substantial and diverse population of Ornithischian dinosaurs.
The Island of Laramidia
Probably the most western of the hawaiian islands, known as Laramidia contained land that was to form Alberta in the north with the American states of Dakota and Montana in the centre with the land that was to become Utah forming the southern part of the island. Formations laid down in the north of this island, the famous Dinosaur Provincial Park like, have provided palaeontologists with a huge array of horned and duck-billed, Ornithischian dinosaurs. Fossils within Utah, animals including the horned dinosaurs Kosmoceratops and Utahceratops from rocks of roughly exactly the same age, indicate that several types of plant-eating dinosaur evolved in the south. The Ohio University scientists have postulated that mountain building and the rising sea levels caused the available habitat for dinosaurs to shrink on Laramidia. Populations became isolated and this was further compounded by later plate tectonic movements that led to the nascent development of what was to end up being the North American Rockies.
New Species Every One Hundred Thousand Years
The team postulate that a new species of large, Ornithischian dinosaur evolved every few hundred thousand years in the period that the mountain ranges and the Western Interior Seaway isolated populations. These geological processes led to a rapid burst of dinosaur evolution in these cut-off populations, in exactly the same way that the isolated populations of animals in the Galapagos archipelago rapidly diversified into new species.
However, this extensive speciation of mega-herbivores was delivered to a conclusion with the continued rise of the embryonic Rock Mountains which eventually forced the Western Interior Seaway to contract. This opened up a sizable, open territory for the Ornithischian dinosaurs to exploit. This reduced the turnover in species with new species evolving at a much slower rate. New species taking higher than a million years to evolve.
A Barrier to Migration
The investigation team warn that their work with the major, herbivorous dinosaur faunas of North America cannot be used as a template to spell out the rise and then your decline in dinosaur diversity on a global scale. However, the rapidly changing geology due to plate movements would have had an influence on the migration of dinosaurs from the Americas into Asia and into South America. The rise of the Rocky Mountains like, would have created a barrier that the dinosaurs couldn’t cross. Only dinosaur species resident north of this barrier might have migrated into Asia and only those species living in the southern part of Laramidia would have had a migration route open for them to South America.