Throughout the last 20 years 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 for example Vagaceratops, Utahceratops and Kosmoceratops in addition to several new genera of Hadrosaurs (duck-billed dinosaurs) have already been described from western North America. Most palaeontologists have already been focused on mapping the faunal distribution and studying the myriad of new plant-eating dinosaur species which were found, but several scientists are now actually looking at the mystery of why so many various kinds of dinosaur evolved in this the main world over the past few million years of the Cretaceous.
Diversity Explanation Is based on the Geology
For 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 a huge, inland seaway that split North America into some islands, may have been the catalysts for an explosion in megafauna diversity. The investigation 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 claim 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 author of the paper and a post-doctoral student at the University commented that over the past few decades palaeontologists have become increasingly conscious of the huge range of various kinds of plant-eating dinosaur that roamed the thing that was to end up being the United States and Canada. However, immediately, ahead of the Cretaceous mass extinction, there have been just a few dominant dinosaur species across the complete continent. This phenonmenon has yet to be fully explained.
Examining the Geological Record of North America
The investigation team set out to examine the geological record of the thing that was to end up being the continent of North America, focusing on the United States and Canada. Throughout the Campanian faunal stage of the Cretaceous, a amount of time in the Earth’s history that roughly pertains 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 a lot of the continental landmass under an inland sea (known while 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 the mass extinction event 65 million years ago, there clearly 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 fall in the amount of 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 through the Early Cretaceous there clearly was a substantial quantity 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 the thing that 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 forming of a massive 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 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 some 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 by having an amazing variety of marine reptile fossils to review – Dolichorhynchops, Elasmosaurs and huge Mosasaurs such as for example Tylosaurus.
The Ohio based research team have focused on the dinosaur fossils which were 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 substantial and diverse population of Ornithischian dinosaurs.
The Island of Laramidia
The most western of the islands, called Laramidia contains land that has been to form 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 with this island, the famous Dinosaur Provincial Park for example, have provided palaeontologists with a huge range of horned and duck-billed, Ornithischian dinosaurs. Fossils within Utah, animals including 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 the thing that 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 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 finish 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 more than a million years to evolve.
A Barrier to Migration
The investigation team warn that their work with the major, herbivorous dinosaur faunas of North America cannot be used as a template to describe the rise and then the decline in dinosaur diversity on a global scale. However, the rapidly changing geology caused by plate movements could 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, could 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 element of Laramidia could have had a migration route open to them to South America.
