Fennek, polar bear
Vulpes zerda (Zimmermann, 1780), Ursus maritimus Phipps, 1774
Behind a little showcase there is a small fox with huge auricles. From our point of view it is hard to see. So here it is.
What big ears it has, even bigger than those of the polar bear!
How are this auricles useful for survival?
This fox lives in a hot desert. What is one of the biggest threats it encounters? It is: overheating. It has to get rid of excess heat. The big auricles in combination with a small body [make the surface/volume ratio big and therefore] enhance the loss of heat. The polar bear, on the other hand, is at risk to be hypothermic. It has to retain its heat. It has a big body combined with little auricles. This [makes the surface/volume ratio small and therefore] diminishes the loss of heat.
(The heat production is proportional to the body volume; the heat loss is proportional to the body surface)