Over the last twenty years approximately, palaeontologists studying the Late Cretaceous fauna of North America have discovered a fantastic variety of Ornithischian dinosaurs in strata laid down between 80 million and 70 million years ago. Several horned dinosaurs such as Vagaceratops, Utahceratops and Kosmoceratops as well as a number of new genera of Hadrosaurs (duck-billed dinosaurs) have been described from western North America. Most palaeontologists have been dedicated to 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 looking at the mystery of why so many various kinds of dinosaur evolved in this part of the world over the last few million years of the Cretaceous.
Diversity Explanation Lies in the Geology
For one team of researchers based at Ohio University, the explanation concerning dinosaur diversity lies in the geology. The rise of the Rocky Mountain range and the looks and then disappearance of a massive, inland seaway that split North America into some islands, may have been the catalysts for an explosion in megafauna diversity. The study team from the University’s Heritage College of Osteopathic Medicine have experienced their paper published in the on line scientific journal PloS One (public library of science). what dinosaur has 500 teeth They suggest 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 writer of the paper and a post-doctoral student at the University commented that over the past few decades palaeontologists have become increasingly alert to the huge selection of various kinds of plant-eating dinosaur that roamed that which was to become the United States and Canada. However, immediately, prior to the Cretaceous mass extinction, there have been only some dominant dinosaur species across the whole continent. This phenonmenon has yet to be fully explained.
Examining the Geological Record of North America
The study team attempted to examine the geological record of that which was to become the continent of North America, emphasizing 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 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 ago up before mass extinction event 65 million years ago, there was less extensive plate activity. This coincided with a decline in the amount of genera of dinosaur known from the fossil record. Palaeontologists have interpreted this as evidence as a drop in the amount of dinosaur species surviving 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 was a considerable level of geological activity in the western United States. Several processes involving subduction, the movement of ocean crust into the Earth’s mantle occurred along that which was to become the western coast of North America. These immense geological forces caused the western part of the Americas to be lifted up and this resulted in the formation of a massive 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 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 some 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 by having an amazing variety of marine reptile fossils to study – Dolichorhynchops, Elasmosaurs and huge Mosasaurs such as Tylosaurus.
The Ohio based research team have dedicated to 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
Probably the most western of the hawaiian islands, called Laramidia contains land that was to form Alberta in the north with the American states of Dakota and Montana in the middle with the land that was to become Utah forming the southern part 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 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 was further compounded by later plate tectonic movements that resulted in the nascent development of that which was to become 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 at that 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 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 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 higher than a million years to evolve.
A Barrier to Migration
The study team warn that their focus 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 an international scale. However, the rapidly changing geology caused by plate movements might have had an influence within the migration of dinosaurs from the Americas into Asia and into South America. The rise of the Rocky Mountains as an example, might have created a barrier that the dinosaurs couldn’t cross. Only dinosaur species resident north of the barrier may have migrated into Asia and only those species surviving in the southern element of Laramidia might have had a migration route open in their mind to South America.