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Geological Changes Spurred Dino Diversity

Paleogeographic maps of North America during the (A) late Campanian (~75 million years ago) and (B) late Maastrichtian (~65 million years ago). Maps courtesy of Ron Blakey, Colorado Plateau Geosystems.

New duck-billed and horned dinosaur species in western North America evolved at a blistering pace between 70 and 80 million years ago – blistering by evolutionary standards, of course, which means that new species appeared over spans of hundreds of thousands of years rather than millions of years.

Later this species growth appears to weaken, according to the fossil record, with new species evolving less frequently.

So what happened in the 15 million-year span to swing the evolutionary pendulum from lots of dinosaur species to fewer dinosaur species?

Important geological and ecological changes, including the rise of the Rocky Mountains and the emergence – and then disappearance – of an ocean, triggered the seismic evolutionary shifts, according to new NC State and Ohio University research.

In a new paper in the journal PLoS ONE, researchers Terry Gates, Lindsay Zanno and Albert Prieto-Márquez show that both the formation of two mountain ranges and of a major body of water carved up portions of western North America into islands. These profound geological changes, occurring between 80 and 70 million years ago, isolated dinosaurs.

“Isolating populations allows them to evolve new features more rapidly, especially when skull ornamentation such as head crests and horns play a role,” Gates said.

A few million years later, however, more geological changes occurred. The Rocky Mountains kept growing, which caused the island-forming ocean to dissipate. Able to more widely roam across North America, dinosaurs evolved new species more slowly.

Gates and his colleagues caution that this scientific sleuthing represents what they believe happened in western North America and does not necessarily apply to other dinosaurs in other parts of the world.

Gates is a research scientist at NC State who also holds a postdoctoral fellow appointment at Ohio University’s Heritage College of Osteopathic Medicine. Zanno is an assistant research faculty member at NC State and the director of the Paleontology and Geology Research Laboratory at the Nature Research Center of the North Carolina Museum of Natural Sciences. Prieto-Márquez is a Humboldt postdoctoral associate at the Bavarian State Collection for Paleontology and Geology in Munich, Germany.