During the last two decades or so, palaeontologists studying the Late Cretaceous fauna of North America have found an amazing variety 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 along with a number of new genera of Hadrosaurs (duck-billed dinosaurs) have now been described from western North America. Most palaeontologists have now been centered on mapping the faunal distribution and studying the myriad of new plant-eating dinosaur species which were found, but a number of scientists are now actually turning to the mystery of why so many various kinds of dinosaur evolved in this area of the world over the last few million years of the Cretaceous.

Diversity Explanation Lies in the Geology

For just one team of researchers based at Ohio University, the explanation regarding dinosaur diversity lies in the geology. The rise of the Rocky Mountain range and the look and then disappearance of a massive, inland seaway that split North America into a series of islands, may have been the catalysts for an explosion in megafauna diversity. The research team from the University’s Heritage College of Osteopathic Medicine have had their paper published in the online scientific journal PloS One (public library of science).  what dinosaur has 500 teeth They state that the rapid changing geology resulted in populations of animals being isolated which can 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 in the last few decades palaeontologists have become increasingly conscious of the huge selection of various kinds of plant-eating dinosaur that roamed what was to become the United States and Canada. However, immediately, prior to the Cretaceous mass extinction, there have been only a few dominant dinosaur species across the entire 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 what was to become the continent of North America, concentrating 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 ago to 74 million years ago there was extensive plate tectonic activity that resulted in mountain ranges being pushed up and the sinking of much of the continental landmass under an inland sea (known whilst 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 ago up until the mass extinction event 65 million years ago, there was less extensive plate activity. This coincided with a decline in the number of genera of dinosaur known from the fossil record. Palaeontologists have interpreted this as evidence as a fall in the number of dinosaur species residing 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 considerable number of geological activity in the western United States. Several processes involving subduction, the movement of ocean crust on to the Earth’s mantle occurred along what was to become the western coast of North America. These immense geological forces caused the western area of the Americas to be lifted up and this resulted in the forming of an enormous 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 the 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 behind in places as far apart as Alberta and Kansas have provided palaeontologists having an amazing variety of marine reptile fossils to examine – Dolichorhynchops, Elasmosaurs and huge Mosasaurs such as for example Tylosaurus.

The Ohio based research team have centered on 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 considerable and diverse population of Ornithischian dinosaurs.

The Island of Laramidia

Probably the most western of the islands, referred to as Laramidia consisted of land that has been to make Alberta in the north with the American states of Dakota and Montana in the middle with the land that has been to become Utah forming the southern area of the island. Formations laid down in the north of the island, the famous Dinosaur Provincial Park as an example, have provided palaeontologists with a massive selection of horned and duck-billed, Ornithischian dinosaurs. Fossils found in Utah, animals such as 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 is further compounded by later plate tectonic movements that resulted in the nascent development of what was to become 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 resulted in 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 an end with the continued rise of the embryonic Rock Mountains which eventually forced the Western Interior Seaway to contract. This exposed a large, 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 greater than a million years to evolve.

A Barrier to Migration

The research team warn that their work on the major, herbivorous dinosaur faunas of North America can not be used as a template to describe the rise and then the decline in dinosaur diversity on a global scale. However, the rapidly changing geology caused by plate movements could have had an influence on the migration of dinosaurs from the Americas into Asia and into South America. The rise of the Rocky Mountains as an example, could have created a barrier that the dinosaurs could not cross. Only dinosaur species resident north of the barrier could have migrated into Asia and only those species residing in the southern part of Laramidia could have had a migration route open for them to South America.

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