Monday, December 20, 2010

What's an "Ice Age Mammal?"

Nice story on musk oxen by Natalie Angier in the NYTimes (  She's an excellent and entertaining nature/science writer (check out her book, "The Canon," some time), and she does a great job of describing these shaggy brown beasts as icons of the Arctic and as resilient holdovers from the last ice age.

But that's not what stuck in my mind after I finished reading "Musk Oxen Live to Tell a Survivor's Tale." 

When she described musk oxen as "holdovers from the Pleistocene," as has been so often said of them before, my admittedly strange paleo-nerd imagination did an unexpected double take.  First came the intended imagery of ice sheets, mammoths, and wooly rhinos.  But then the other Arctic animals mentioned in the piece - the polar bears, caribou, and such - entered the picture as well and triggered a question that I've never heard asked before. 

Why do we think of hairy Arctic musk oxen as survivors of the Pleistocene epoch, and of mammoths and wooly rhinos as "ice age mammals," when virtually ALL of the mammal species alive today also lived through the last ice age and are therefore also survivors of the Pleistocene? 

Polar bears, caribou, and real oxen (aurochs, anyway) were here on Earth along with musk oxen during the peak of the last ice age 20,000 years ago, and so were tropical African elephants and rhinos.  So were armadillos, and beavers, and whales, and squirrels, and manatees. So were people, for that matter.  Technically speaking, we too are "ice age mammals" and resilient survivors of the Pleistocene.  In fact, most of the 200,000-odd year history of anatomically modern Homo sapiens took place during that geological epoch,  mainly during times when mile-thick slabs of ice smothered Canada. 

I suppose some of the confusion arises from how our imaginations tend to envision the distant past.  When we think "ice age" we immediately think of ice sheets, but they only covered the higher latitudes and altitudes during the repeated continental glaciations of the last 2-3 million years.  The tropics were still tropical, if a bit cooler and generally less rainy than they are now, and few animals went extinct as a result of climatic changes during the last glaciation.  There were plenty of ice-free, even toasty places to live in back then, as there are today.

We also focus on mammoths and wooly rhinos and such because they're cool, and because they're not with us any more.  But that's because our spear-toting ancestors killed them, not primarily because of climate change.  Yes, some scientists do think otherwise, but they're in the minority among their peers, and their arguments just don't stand up well against the overwhelming evidence for a non-climatic cause.  To put it simply and, to me at least, decisively; if climate change killed off so many of the big mammals at the end of the last ice age, then why didn't it do so when the previous dozens of ice ages ended? 

Anyhow, this mini-epiphany was a nice little thrill for me.  I like it when something makes me snap out of a mistaken or clouded point of view, leaving me wondering why I didn't notice this or that amazing thing before. 

Hey, everybody - I'm an ice age mammal!  A hold-over from the Pleistocene (as many of my students would likely attest). 

And if you can read this... so are you.     :)

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