Throughout the last 20 years roughly, palaeontologists studying the Late Cretaceous fauna of North America have discovered an incredible number 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 numerous 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 numerous scientists are actually embracing the mystery of why so many different types of dinosaur evolved in this the main world during 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 huge, inland seaway that split North America into some islands, could 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 online scientific journal PloS One (public library of science). what dinosaur has 500 teeth They declare that the rapid changing geology resulted in populations of animals being isolated which 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 have grown to be increasingly conscious of the huge array of different types of plant-eating dinosaur that roamed that which was to become 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 study team attempt 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 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 until 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 residing in North America towards the 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 number 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 the main 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 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 having an amazing number 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 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 a considerable and diverse population of Ornithischian dinosaurs.
The Island of Laramidia
The most western of the islands, referred to as Laramidia contains land that has been to make Alberta in the north with the American states of Dakota and Montana at the center with the land that has been to become Utah forming the southern the main island. Formations laid down in the north of the island, the famous Dinosaur Provincial Park like, have provided palaeontologists with a huge array of horned and duck-billed, Ornithischian dinosaurs. Fossils within Utah, animals such as the horned dinosaurs Kosmoceratops and Utahceratops from rocks of roughly 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 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 in the period 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 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 finish with the continued rise of the embryonic Rock Mountains which eventually forced the Western Interior Seaway to contract. This opened up 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 higher than a million years to evolve.
A Barrier to Migration
The study team warn that their work on the major, herbivorous dinosaur faunas of North America can’t be used as a template to explain the rise and then your decline in dinosaur diversity on a worldwide scale. However, the rapidly changing geology brought on by 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 couldn’t cross. Only dinosaur species resident north of the barrier may have migrated into Asia and only those species residing in the southern part of Laramidia would have had a migration route open in their mind to South America.