Climate change led to waves of mammal evolution 65m yrs ago in North America

Washington, Dec 27 (ANI): A novel study has identified six distinct, consecutive waves of mammal species diversity, or "evolutionary faunas" in the last 65 million years of natural history in North America.

And researchers suggest that climate change might have led to these changes.

"Although we've always known in a general way that mammals respond to climatic change over time, there has been controversy as to whether this can be demonstrated in a quantitative fashion," said Brown University evolutionary biology Professor Christine Janis.

"We show that the rise and fall of these faunas is indeed correlated with climatic change - the rise or fall of global paleotemperatures - and also influenced by other more local perturbations such as immigration events," he stated.

Specifically, of the six waves of species diversity that Janis and her Spanish collaborators describe, four show statistically significant correlations with major changes in temperature.

The two transitions that show a weaker but still apparent correlation with the pattern correspond to periods when mammals from other continents happened to invade in large numbers, said Janis, who is the study's senior and second author.

What the authors found is six distinct and consecutive groupings of mammal species that shared a common rise, peak and decline in their numbers.

For example, the "Paleocene fauna" had largely given way to the "early-middle Eocene fauna" by about 50 million years ago. Moreover, the authors found that these transfers of dominance correlated with temperature shifts, as reflected in data on past levels of atmospheric oxygen (determined from the isotopes in the fossilized remains of deep sea microorganisms).

By the numbers, the research showed correlations between species diversity and temperature change, but qualitatively, it also provided a narrative of how the traits of typical species within each wave made sense given the changes in vegetation that followed changes in climate.

The finding appeared online this week in the Proceedings of the National Academy of Sciences. (ANI)