Why do animals of southern latitudes and tropics, as a rule, have more protruding body parts than animals

Why do animals of southern latitudes and tropics, as a rule, have more protruding body parts than animals of northern latitudes and polar regions?

For example, elephants and desert foxes have enhanced heat transfer through their ears.
Alain’s rule is an ecological-morphological law discovered and substantiated by Joel Asaf Alain in 1877. According to this rule, in warm-blooded animals the protruding parts of the body in cold climates will be shorter than in related species in warm regions. Due to this, animals living in cold natural conditions acquire a smaller body surface and, as a result, lose less heat. An example of the action of the Alena rule is representatives of the Canine family from different regions of the world. Thus, the smallest (relative to body length) ears and nose in this family are observed in the blue fox inhabiting the Arctic, and the largest in the fennec fox inhabiting the deserts of North Africa (mainly in the Sahara).