Throughout the last two decades or so, palaeontologists studying the Late Cretaceous fauna of North America have found a fantastic selection of Ornithischian dinosaurs in strata laid down between 80 million and 70 million years ago. A number of horned dinosaurs such as for example 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 focused on mapping the faunal distribution and studying the myriad of new plant-eating dinosaur species that have been found, but several scientists are now actually turning to the mystery of why so many several types of dinosaur evolved in this the main 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, could have been the catalysts for an explosion in megafauna diversity. The study 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 declare 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 in the last few decades palaeontologists are becoming increasingly alert to the huge range of several types of plant-eating dinosaur that roamed that which was to end up being the United States and Canada. However, immediately, prior to the Cretaceous mass extinction, there were just 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 study team set out to examine the geological record of that which 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 time in the Earth’s history that roughly relates to 83 million years ago to 74 million years ago there clearly was 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 while 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 before mass extinction event 65 million years ago, 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 drop 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 through the Early Cretaceous there clearly was a substantial number of geological activity in the western United States. A number of processes involving subduction, the movement of ocean crust down into the Earth’s mantle occurred along that which 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 synthesis of an enormous mountain range that extended from Alberta (Canada) in a south-western direction to as far south while 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 put aside in places as far apart as Alberta and Kansas have provided palaeontologists having an amazing selection of marine reptile fossils to examine – Dolichorhynchops, Elasmosaurs and huge Mosasaurs such as for example Tylosaurus.
The Ohio based research team have focused on the dinosaur fossils that have been present 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 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 the main island. Formations laid down in the north of the island, the famous Dinosaur Provincial Park for example, have provided palaeontologists with a massive range of horned and duck-billed, Ornithischian dinosaurs. Fossils present in Utah, animals like 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 that which 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 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 finish with the continued rise of the embryonic Rock Mountains which eventually forced the Western Interior Seaway to contract. This opened up 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 more than a million years to evolve.
A Barrier to Migration
The study team warn that their work with the major, herbivorous dinosaur faunas of North America can not 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 brought on by plate movements could have had an influence within the migration of dinosaurs from the Americas into Asia and into South America. The rise of the Rocky Mountains for example, could have created a barrier that the dinosaurs could not cross. Only dinosaur species resident north of the barrier would have migrated into Asia and only those species residing in the southern part of Laramidia could have had a migration route open in their mind to South America.