What Triggered North American Dinosaur Diversity?
August 4, 2012

Rocky Mountains, Ancient Seaway May Have Spurred Dinosaur Diversity

redOrbit Staff & Wire Reports - Your Universe Online

The rise of the Rocky Mountains and the arrival of a seaway that divided North America into three distinct sections may have been the catalyst for the evolution of new species of dinosaurs, claims a new study published in Thursday's edition of the journal PLoS ONE.

The study, which was led by Ohio University (OU) postdoctoral researcher Terry Gates, could explain evolutionary and migratory patterns of North American duck-billed and horned dinosaurs in the days prior to their extinction some 65 million years ago.

"Over the past century, paleontologists have found a wide variety of dinosaurs in rocks dating to around 75 million years ago, but right before the asteroid hit at the end of the Cretaceous, there appeared to be fewer species in North America," Gibbs of the OU Heritage College of Osteopathic Medicine said. "The reason for this discrepancy in dinosaur diversity has never been adequately explained."

In an attempt to provide such an explanation, Gibbs and his colleagues analyzed geological records of the western part of the continent, paying special attention to trends in mountain and ocean formation from between 70 and 80 million years ago -- a time in which there is believed to have been an "explosion" in the number of dinosaur species, after which they became less diverse.

"During the early to middle Cretaceous, geological forces lifted the western United States, creating a huge mountain range (the Sevier Mountains) that extended in a line from the American southwest through Alberta, Canada," the university said in an August 2 statement. "The area just to the east of the new mountain range flexed downward, creating a shallow North American seaway (known as the Western Interior Seaway) that flooded the continent from the Canadian arctic to the Gulf of Mexico."

"This seaway cut the continent into three large islands to the north, east and west that were densely populated with dinosaurs. The dinosaurs of the west lived on an island known as Laramidia. Most fossil discoveries have been made in the area of the northern part of the island, in places such as Alberta, South Dakota and Montana, while dinosaurs have been found only recently in the former areas of southern Laramidia," they added.

These new discoveries illuminate how the gigantic creatures would have evolved on islands with changing geography. With the rising of the Sevier Mountains and the growth of the seaway, the dinosaur habitat on Laramidia would have become smaller. Later on, as tectonic plates shifted to give rise to what would become the Rocky Mountains, the barriers would have led to isolation of both the northern and southern populations of the crested duck-billed and horned plant-eating dinosaurs, the researchers said. That isolation could have led to increased diversity.

"The new species of duck-billed and horned dinosaurs were being born at an astounding rate of every few hundred thousand years during the brief time when the two mountain ranges and the seaway coexisted," Gates said. "Eventually, however, the continued rise of the Rocky Mountains would evict the seaway from the continent's interior. Gates and his colleagues argue that this second geological change opened up a wide territory for duck-billed and horned dinosaurs to roam, that, in turn, reduced how fast new species evolved in the region to every few million years."