During the last twenty years or so, palaeontologists studying the Late Cretaceous fauna of North America have found a fantastic number of Ornithischian dinosaurs in strata laid down between 80 million and 70 million years ago. Numerous horned dinosaurs such as Vagaceratops, Utahceratops and Kosmoceratops as well as several 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 that have been found, but several scientists are now embracing the mystery of why so many different types of dinosaur evolved in this part of the world during 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 is based on the geology. The rise of the Rocky Mountain range and the appearance and then disappearance of an enormous, inland seaway that split North America into a series of 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 had 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 resulted in populations of animals being isolated that might 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 within the last few decades palaeontologists are becoming increasingly aware of the huge selection of different types 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 were just 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 study team attempted to examine the geological record of what was to end up being the continent of North America, emphasizing the United States and Canada. Throughout the Campanian faunal stage of the Cretaceous, a amount of time in the Earth’s history that roughly relates to 83 million years back to 74 million years back there is 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 back up before the mass extinction event 65 million years back, there is 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 living 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 is a considerable amount of geological activity in the western United States. Numerous processes involving subduction, the movement of ocean crust down into 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 part of the Americas to be lifted up and this resulted in the forming of a huge 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 with this 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 with an amazing number 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 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 considerable and diverse population of Ornithischian dinosaurs.
The Island of Laramidia
Probably the most western of the hawaiian islands, referred to as Laramidia consisted of 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 part of the island. Formations laid down in the north with this island, the famous Dinosaur Provincial Park like, have provided palaeontologists with an enormous selection of horned and duck-billed, Ornithischian dinosaurs. Fossils present in Utah, animals including the horned dinosaurs Kosmoceratops and Utahceratops from rocks of roughly exactly the same age, indicate that different 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 is further compounded by later plate tectonic movements that resulted in 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 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 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 a conclusion 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 greater 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’t 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 due to plate movements would have had an influence over the migration of dinosaurs from the Americas into Asia and into South America. The rise of the Rocky Mountains like, would have created a barrier that the dinosaurs could not cross. Only dinosaur species resident north with this barrier could have migrated into Asia and only those species living in the southern part of Laramidia would have had a migration route open to them to South America.