Over the last 20 years approximately, palaeontologists studying the Late Cretaceous fauna of North America can see an amazing selection of Ornithischian dinosaurs in strata laid down between 80 million and 70 million years ago. A number of horned dinosaurs such as Vagaceratops, Utahceratops and Kosmoceratops in addition to numerous new genera of Hadrosaurs (duck-billed dinosaurs) have now been described from western North America. Most palaeontologists have now been dedicated to mapping the faunal distribution and studying the myriad of new plant-eating dinosaur species which were found, but numerous scientists are now actually looking at the mystery of why so many various kinds of dinosaur evolved in this area of the world during the last few million years of the Cretaceous.

Diversity Explanation Is based on the Geology

For starters team of researchers based at Ohio University, the explanation as to dinosaur diversity is based on 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, might have been the catalysts for an explosion in megafauna diversity. The research team from the University’s Heritage College of Osteopathic Medicine experienced their paper published in the online scientific journal PloS One (public library of science).  what dinosaur has 500 teeth They claim 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 composer 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 range of various kinds of plant-eating dinosaur that roamed the thing that 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 research team attempted to examine the geological record of the thing that was to end up being the continent of North America, focusing on the United States and Canada. Throughout the Campanian faunal stage of the Cretaceous, a time in the Earth’s history that roughly pertains to 83 million years back to 74 million years back there clearly 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 because 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 back up before the mass extinction event 65 million years back, there clearly was 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 living in North America towards ab muscles end of the Cretaceous – dinosaur genera became less diverse.

Mountain Building Isolating Populations

Geologists have calculated that during the Early Cretaceous there clearly was a substantial amount of geological activity in the western United States. A number of processes involving subduction, the movement of ocean crust into the Earth’s mantle occurred along the thing that was to end up being the western coast of North America. These immense geological forces caused the western area of the Americas to be lifted up and this led to the synthesis of a huge mountain range that extended from Alberta (Canada) in a south-western direction to as far south because 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 a series of large islands. This sea (Western Interior Seaway), teemed with life and the marine deposits put aside in places as far apart as Alberta and Kansas have provided palaeontologists with an amazing selection of marine reptile fossils to review – Dolichorhynchops, Elasmosaurs and huge Mosasaurs such as Tylosaurus.

The Ohio based research team have dedicated to the dinosaur fossils which were 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 substantial and diverse population of Ornithischian dinosaurs.

The Island of Laramidia

Probably the most western of the hawaiian islands, called Laramidia contains land which was to create Alberta in the north with the American states of Dakota and Montana in the middle with the land which was to become Utah forming the southern area of the island. Formations laid down in the north of this island, the famous Dinosaur Provincial Park for instance, have provided palaeontologists with a huge range of horned and duck-billed, Ornithischian dinosaurs. Fossils found in Utah, animals including the horned dinosaurs Kosmoceratops and Utahceratops from rocks of roughly exactly the same age, indicate that various kinds 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 the thing that was to end up being the North American Rockies.

New Species Every One Hundred Thousand Years

The team postulate a 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 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 brought to an end with the continued rise of the embryonic Rock Mountains which eventually forced the Western Interior Seaway to contract. This exposed 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 more than a million years to evolve.

A Barrier to Migration

The research team warn that their work with the major, herbivorous dinosaur faunas of North America can’t be used as a template to explain the rise and then a decline in dinosaur diversity on a worldwide 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 for instance, would have created a barrier that the dinosaurs couldn’t cross. Only dinosaur species resident north of this barrier could have migrated into Asia and only those species living in the southern section of Laramidia would have had a migration route open for them to South America.

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