How the Rockies prepared mammals for the cold

Chuck Bednar for redOrbit.com – @BednarChuck

Nearly 34 million years ago, European mammals were wiped out en masse due to plummeting temperatures during an event known as the Grande Coupure, yet at this same time, their North American counterparts were largely unfazed. Why?

A team of researchers from the Senckenberg Research Institutes in Germany, the University of Helsinki in Finland and Brown University in Rhode Island found the reason for this phenomenon – the rise of the Rocky Mountains across western North America during this transitional period that took place between the Eocene and Oligocene periods.

As they reported in a study published Wednesday in the Proceedings of the Royal Society B, the authors analyzed the fossil record of both continents, as well as previous oxygen isotope data that had revealed precipitation patterns and tectonic models of the Rockies’ growth. They discovered that North American mammals survived due to adaptive change, driven by the mountains.

European mammals had no chance to get acclimated

The authors explained that the Rockies spread southward in three phases, originating in Canada more than 50 million years ago, then through Idaho and finally into Nevada 23 million years ago. The fossil data, meanwhile, showed a decrease in precipitation in the interior regions, as well as significant shifts in mammal populations, including an almost total loss of primates.

Since these shifts occurred over the span of tens of millions of years, North American mammals had already adapted by time the Grand Coupure happened 34 million years ago. Conversely, in Europe, tectonic developments had little impact on the climate, so mammals there experienced a sudden change in weather. They were not prepared and their chances to survive had been greatly diminished, so they were ultimately overrun by well-adapted Asian mammals.

Inside the research with authors Jussi Eronen and Christine Janis

Jussi Eronen of Senckenberg Institutes, one of the featured authors of the study, told redOrbit that there had been some confusion stemming from previous research regarding when the Rockies originally uplifted. Studies from the 1980s and 90s claimed that it had only taken place over the past 20 million years, and was not seen as a viable reason for this phenomenon until the 2000s, when geologists first indicated that the uplift was older than previously believed.

Eronen noted that he and fellow author Christine Janis of Brown University first started working together “to bring in the North American and Eurasian mammal record” a few years ago. He had just started working with Andreas Mulch at Senckenberg BiK-F during a Humboldt fellowship in 2012 when he was “introduced to this new reading of the tectonic record of North America.”

It wasn’t long until he and Janis were able to connect the dots, he added.

“Previously,” Janis told redOrbit, “some people had used the relative lack of response in the North American mammals at the Eocene-Oligocene boundary as evidence that climatic change had little effect on mammals. This paper shows that you have to look at the whole picture.”

“Regional topographic changes might also have a profound effect,” she added. “[The research] shows how mammals can be excellent indicators of past climatic conditions, and how sensitive they are to climatic change, which has implications for the future world.”

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Source: http://www.redorbit.com/news/science/1113403729/how-the-rockies-prepped-mammals-for-the-cold-060415/