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Throughout the last two decades roughly, palaeontologists studying the Late Cretaceous fauna of North America can see an incredible variety 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 a number of new genera of Hadrosaurs (duck-billed dinosaurs) have been described from western North America. Most palaeontologists have been focused on mapping the faunal distribution and studying the myriad of new plant-eating dinosaur species which have been found, but a number of scientists are now actually turning to the mystery of why so many various kinds of dinosaur evolved in this the main world over the last few million years of the Cretaceous.
Diversity Explanation Is based on 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, could 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 suggest that the rapid changing geology led to populations of animals being isolated which might 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 aware of the huge array of various kinds 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 have been only some 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 set out to examine the geological record of what was to end up being the continent of North America, concentrating on the United States and Canada. Through 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 is 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 as 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 is 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 drop in the number of 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 an amazing amount of geological activity in the western United States. Numerous processes involving subduction, the movement of ocean crust on to 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 formation of a huge mountain range that extended from Alberta (Canada) in a south-western direction to as far south as the southern United States. The region to the east with 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 left out in places as far apart as Alberta and Kansas have provided palaeontologists by having an amazing variety of marine reptile fossils to review – Dolichorhynchops, Elasmosaurs and huge Mosasaurs such as Tylosaurus.
The Ohio based research team have focused on the dinosaur fossils which have been 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 an amazing and diverse population of Ornithischian dinosaurs.
The Island of Laramidia
The absolute most western of the hawaiian islands, referred to as Laramidia contained land which was to create Alberta in the north with the American states of Dakota and Montana in the centre with the land which was to become Utah forming the southern the main island. Formations laid down in the north with this island, the famous Dinosaur Provincial Park for example, have provided palaeontologists with a massive array of horned and duck-billed, Ornithischian dinosaurs. Fossils within Utah, animals like the horned dinosaurs Kosmoceratops and Utahceratops from rocks of roughly the exact 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 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 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 a conclusion with the continued rise of the embryonic Rock Mountains which eventually forced the Western Interior Seaway to contract. This exposed 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 research team warn that their work on the major, herbivorous dinosaur faunas of North America can not be used as a template to explain the rise and then the decline in dinosaur diversity on a global scale. However, the rapidly changing geology caused by plate movements might 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 example, might have created a barrier that the dinosaurs could not cross. Only dinosaur species resident north with this barrier might have migrated into Asia and only those species residing in the southern part of Laramidia might have had a migration route open for them to South America.
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