I read something not too long ago that made sense to me. Mammals in extreme cold climates have evolved larger in weight in order to keep their core temperature warm in winter. For example, a moose in Alaska that is twice the weight of a Wyoming moose has less then twice the "surface area" of the smaller variety. Thicker, to insulate innards ( the longer legs probably came about from evolving in deep snow).
It seems to be consistent with: wolves, deer ( Alberta whitetail vs Texas), coyotes, rabbits ( snowshoe vs. cottontail ), and so on. Critters that nest-up in cold weather don't seem to change ( mice, squirrel, etc).
I'm not sure of the source where I read it, but I think it was one of the Wolfe Publishing's mags, "Rifle" or "Successful Hunter".
Thoughts?????
Mark