Over 65 million years North American mammal evolution has tracked with climate change

Dec 26, 2011
This painting by artist Carl Buell depcits a scene from the late Eocene of North America. The rhino‑like animals in the background are brontotheres. The pony‑sized Hyracodon, a closer relative of living rhinos, in the foreground. Credit: Courtesy of Carl Buell

Climate changes profoundly influenced the rise and fall of six distinct, successive waves of mammal species diversity in North America over the last 65 million years, shows a novel statistical analysis led by Brown University evolutionary biologists. Warming and cooling periods, in two cases confounded by species migrations, marked the transition from one dominant grouping to the next.

History often seems to happen in waves – fashion and musical tastes turn over every decade and empires give way to new ones over centuries. A similar pattern characterizes the last of natural history in , where a novel quantitative analysis has identified six distinct, consecutive waves of mammal species diversity, or "evolutionary faunas." What force of history determined the destiny of these groupings? The numbers say it was typically .

"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."

Specifically, of the six waves of species diversity that Janis and her Spanish collaborators describe online this week in the Proceedings of the National Academy of Sciences, 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 paper's senior and second author.

Previous studies of the potential connection between climate change and mammal species evolution have counted total species diversity in the fossil record over similar time periods. But in this analysis, led by postdoctoral scholar Borja Figueirido, the scientists asked whether there were any patterns within the species diversity that might be significant. They were guided by a similar methodology pioneered in a study of "evolutionary faunas" in marine invertebrates by Janis' late husband Jack Sepkoski, who was a paleontologist at the University of Chicago.

What the authors found is six distinct and consecutive groupings of 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 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. For example, after a warming episode about 20 million years in the early Miocene epoch, the dominant vegetation transitioned from woodland to a savannah-like grassland. It is no surprise, therefore, that many of the herbivores that comprised the accompanying "Miocene fauna" had high-crowned teeth that allowed them to eat the foods from those savannah sources.

To the extent that the study helps clarify scientists' understanding of evolution amid climate changes, it does not do so to the extent that they can make specific predictions about the future, Janis said. But it seems all the clearer that climate change has repeatedly had meaningful effect over millions of years.

"Such perturbations, related to anthropogenic climatic change, are currently challenging the fauna of the world today, emphasizing the importance of the fossil record for our understanding of how past events affected the history of faunal diversification and extinction, and hence how future climactic changes may continue to influence life on earth," the authors wrote in the paper.

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Hayduke2000
1.2 / 5 (21) Dec 26, 2011
There is a jarring jump between the description of ancient evolutionary patterns and anthropogenic climate change.

The temperature changes of the Miocene are not quantified, therefore, there is no way to compare them with observed changes in global average surface temperatures observed today. Different is not the same. That was then, this is now.

There is no justification for using Miocene evoutionary patterns to prop up modern theories of climate variation.
Nanobanano
1.9 / 5 (15) Dec 26, 2011
There is no justification for using Miocene evoutionary patterns to prop up modern theories of climate variation.


Anything before modern instruments was invented is at best circumstancial or anecdotal.

Obviously some fossils would require common sense relationships to temperature and climate, but without actual instrumentation, who really "knows" what conditions an extinct animal was capable of surviving?

Polar bears survive in the arctic where it's -40C, while black bears survive in Louisiana, where it rarely gets below 0C. Most animals can migrate pretty well, unless there's something completely impassible in the way: a canyon, river, ocean, or mountain range...

A continent would allegedly move about 800 miles in 50m years, which is about 11 degrees on the globe. This would likely make a bigger difference in climate over 50m years than would global atmospheric variation (excluding mega-disasters).
Guy_Underbridge
4.2 / 5 (11) Dec 26, 2011
There is a jarring jump between the description of ancient evolutionary patterns and anthropogenic climate change.
Maybe I misread the article, but I never saw AWG mentioned.
MR166
3.1 / 5 (17) Dec 26, 2011
They are making a preemptive strike here just in case some "uninformed" person jumps to the conclusion that the earth might have been warmer in the past or suffered from some sort of cyclical non man made climate changes. Lets face it, 1000s of scientists, all depending on government grants, could not be biased.
GeoGeo
4.8 / 5 (17) Dec 26, 2011
The temperature changes of the Miocene are not quantified, therefore, there is no way to compare them with observed changes in global average surface temperatures observed today. Different is not the same. That was then, this is now.


How horribly incorrect your statement is. I would suggest taking a few classes so as to educate yourself and reading numerous papers. There are plenty of methods that correlate quite well with each other so as to record paleotemperatures accurately and quantitatively (ie. Delta 13C, Delta 18O, Stomatal density, and the list goes on).

The PETM (PaleoceneEocene Thermal Maximum) is just one of many important events to study so that we can better understand the effects that climate change may have today, anthropogenic or not. If you can see how climates were effected in the past by said factors, we can make justified and well founded predictions about what factors play important roles today and how they may or may not effect us.
Parsec
5 / 5 (11) Dec 26, 2011
There is a jarring jump between the description of ancient evolutionary patterns and anthropogenic climate change.

The temperature changes of the Miocene are not quantified, therefore, there is no way to compare them with observed changes in global average surface temperatures observed today. Different is not the same. That was then, this is now.

There is no justification for using Miocene evoutionary patterns to prop up modern theories of climate variation.

I disagree completely. These results do not prop up anything, except provide a serious warning of consequences.

The estimated climate changes and the amounts that temperature changed in the last 65 million years is well documented. They are not part of this study.
jsn3604
1.6 / 5 (12) Dec 26, 2011
"Climate change" must be the "WD-40" of the scientific community.
Parsec
5 / 5 (10) Dec 26, 2011
There are many different ways that temperature can be calculated over paleo-historical times. Most are completely independent, yet they agree. You can argue about one method or another, but several lining up is pretty firm stuff.

You have to make pretty sophisticated arguments to discredit one method or another, or to argue that one or more are not independent of the others.

But just basing an argument on not knowing or understanding what they are is just plain ignorant. Educate yourself - then explain your objections.
GuruShabu
1 / 5 (13) Dec 26, 2011
OMG! I thought climate change had begun with our industrial age!
Mostly after Al Gore movie!
Burnerjack
3.4 / 5 (7) Dec 26, 2011
How did the subject of Earth's temperature fluctuations go from science to religion?
tadchem
2.3 / 5 (8) Dec 27, 2011
"Climate change" must be the "WD-40" of the scientific community.

It certainly lubricates the grant machines well.
Worldnick
not rated yet Dec 28, 2011
Isn't all of this obvious? Climate changes spurs evolution. I thought that was part of the explanation of how evolution works. Being able to survive more successfully in your environment leads to more offspring etc.. How is this news? And further more what's with all these argumentative comments? This whole thing seems like an article and comment section ripped out of the 1800s. Weird.
deepsand
3.5 / 5 (13) Dec 28, 2011
Climate changes spurs evolution


Not quite; genetic mutation drives evolution. Environmental changes select against certain mutations.
deepsand
3 / 5 (10) Dec 28, 2011
Thank you, camshaft, for your top rating of my post.

BTW, why have YOUR POSTS ALL BEEN DELETED? :lol:
p1ll
1 / 5 (5) Dec 30, 2011
I see climate change on the same level as dark matter. Neat theory, but we have yet to grasp how it works and all the factors at play.

If I am not mistaken, there are various supercomputers around the world running climate simulations. Can any of these models accurately predict anything? And they are all running different alghorithms, correct?

Good science easily stands up to challenges, but AGW is not good science. Where are the hurricanes? Where are the "super storms"?

Has there been research to determine wether earth would be better warmer than cold? I'm pretty sure colder Earth and people really start dying
deepsand
3.5 / 5 (11) Dec 30, 2011
If I am not mistaken, there are various supercomputers around the world running climate simulations. Can any of these models accurately predict anything? And they are all running different alghorithms, correct?

The presence or absence of accurately predictive simulations is irrelevant to the underlying Laws of Nature, which, with respect to Radiative Forcing, are long and well understood.