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During the last twenty years or so, palaeontologists studying the Late Cretaceous fauna of North America have discovered a fantastic selection of Ornithischian dinosaurs in strata laid down between 80 million and 70 million years ago. Several horned dinosaurs such as for example Vagaceratops, Utahceratops and Kosmoceratops as well as numerous new genera of Hadrosaurs (duck-billed dinosaurs) have already been described from western North America. Most palaeontologists have already been centered on mapping the faunal distribution and studying the myriad of new plant-eating dinosaur species which have been found, but numerous scientists are now turning to the mystery of why so many several types of dinosaur evolved in this the main world during the last few million years of the Cretaceous.

Diversity Explanation Lies in the Geology

For starters team of researchers based at Ohio University, the explanation as to dinosaur diversity lies in the geology. The rise of the Rocky Mountain range and the appearance and then disappearance of a huge, inland seaway that split North America into a series of islands, may have been the catalysts for an explosion in megafauna diversity. The investigation team from the University’s Heritage College of Osteopathic Medicine have experienced their paper published in the online scientific journal PloS One (public library of science).  what dinosaur has 500 teeth They suggest that the rapid changing geology led to populations of animals being isolated which can explain the patterns of evolution, migration and rapid dinosaur diversification.

Terry Gates, the lead writer of the paper and a post-doctoral student at the University commented that within the last few decades palaeontologists are becoming increasingly alert to 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, ahead of 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 attempted to examine the geological record of what was to end up being the continent of North America, concentrating on the United States and Canada. During the Campanian faunal stage of the Cretaceous, a amount of time in the Earth’s history that roughly pertains to 83 million years back to 74 million years back there is extensive plate tectonic activity that led to mountain ranges being pushed up and the sinking of much of the continental landmass under an inland sea (known since the Western Interior Seaway). At its most extensive, this seaway covered much of North America from Canada to the Gulf of Mexico.

In the later Maastrichtian faunal stage, that lasted from 74 million years back up before mass extinction event 65 million years back, there is less extensive plate activity. This coincided with a decline in how many genera of dinosaur known from the fossil record. Palaeontologists have interpreted this as evidence as a fall in how many dinosaur species residing in North America towards the very end of the Cretaceous – dinosaur genera became less diverse.

Mountain Building Isolating Populations

Geologists have calculated that during the Early Cretaceous there is a considerable quantity of geological activity in the western United States. Several processes involving subduction, the movement of ocean crust down 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 the main Americas to be lifted up and this led to the forming of a huge mountain range that extended from Alberta (Canada) in a south-western direction to as far south since 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 much of the continent and splitting what land remained above sea level into a series of 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 review – Dolichorhynchops, Elasmosaurs and huge Mosasaurs such as for example Tylosaurus.

The Ohio based research team have centered on the dinosaur fossils which have been found in 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 considerable and diverse population of Ornithischian dinosaurs.

The Island of Laramidia

The absolute most western of the islands, known as Laramidia contained land that was to make 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 the main island. Formations laid down in the north of this island, the famous Dinosaur Provincial Park for instance, have provided palaeontologists with a huge array of horned and duck-billed, Ornithischian dinosaurs. Fossils found in Utah, animals such as the horned dinosaurs Kosmoceratops and Utahceratops from rocks of roughly the exact 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 the new species of large, Ornithischian dinosaur evolved every few hundred thousand years during the time 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 the exact 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 taken to an end with the continued rise of the embryonic Rock Mountains which eventually forced the Western Interior Seaway to contract. This opened up a big, 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 more than a million years to evolve.

A Barrier to Migration

The investigation team warn that their work on the major, herbivorous dinosaur faunas of North America cannot be used as a template to explain the rise and then the decline in dinosaur diversity on an international scale. However, the rapidly changing geology caused by plate movements could have had an influence over the migration of dinosaurs from the Americas into Asia and into South America. The rise of the Rocky Mountains for instance, could have created a barrier that the dinosaurs couldn’t cross. Only dinosaur species resident north of this barrier may have migrated into Asia and only those species residing in the southern section of Laramidia could have had a migration route open in their mind to South America.