If you want to be able to withstand the cold it is good to be big. (With heat it is the other way around.)
We all know intuitively that makes sense – but it is in fact down to one of the weirdest mathematical characteristics of objects: when you are small, you have more surface to mass, when you are larger, compared to your mass, you relatively have less surface. It has to do with the difference between stretching two and stretching three dimensions.
You’ll probably get it – and we’re in no need to dig any deeper.
[Although – as we write so much about climate science, we do hope – if you haven’t before – you now suddenly realise why aerosols can actually float in the air – and pebbles cannot.]
Anyway, the empirical evidence says it all: polar bears are the biggest of bears, tundra wolves and Eurasian wolves the largest subspecies of gray wolves – and all gray wolves are larger than southern wolf species.
[And let’s recall these gigantic Dutchmen share some ancestry with Scandinavians, and if perhaps not Arctic, there too you are pretty far up north - the realm of ancient winters.]
The best evidence however comes from the ice age megafauna. Not just mammoths, mastodons and whooly rhinos roamed the frozen plains of North America and Eurasia – also other plus-sized herbivores, like the giant deer (or ‘Irish elk’) and musk oxen.
For each of these species the benefit of having large bodies outweighed to associated extra caloric requirements. It is easier to eat a lot when your mouth and stomach are bigger too.
But what if you were a carnivore in the ice age?
Well, two American evolutionary biologists will agree with your easy answer. They have studied fossil coyote bones and found out just 10,000 years ago [let’s call that the real end of the last ice age] American coyotes [a canine species that uniquely evolved in North America – gray wolf subspecies are actually of Eurasian origin] ‘overlapped in size’ with modern-day wolves*, as the researchers write in their special publication in PNAS.
[*) We don’t quite conclude the same from the weight estimates. Ice age coyotes according to the study weighed 15-25 kilograms – modern coyotes weigh 10-18 kilograms – and Northern Rocky Mountain wolves (a gray wolf subspecies) weighs 32-61 kilograms – yes, indeed, those are the beautiful Yellowstone wolves we reported on earlier.]
Anyway, ice age coyotes were bigger and that keeps our perspective on ice age megafauna simple.
One remarkable thing though to end this story with: the researchers also found that coyote populations were down to their current size of smaller individuals within one thousand years after the megafauna extinctions. That move made them fill a gap in the food chain that proved very lucrative* wherever we humans chased away and hunted down the larger wolf species.
[*) Modern coyotes walk freely through all US states except Hawaii - wolves are confined mostly to Canadian border states (although in the US there is a comeback going on, just like in Europe).]
© Rolf Schuttenhelm | www.bitsofscience.org