The size and shape of an animal has an impact on how it loses energy. The more surface area it has, compared to its mass, the easier it loses heat. Elephants have a large mass and comparatively little surface area, because they are well rounded. Large ears are used for cooling.
On the other hand, giraffes have a large surface area compared to their mass.
These concepts are explained in human terms at this link. Put simply, if you are well rounded you will stay warmer than if you are thin and spindly.