Why are Snow leopards and leopards different?

Leopards (Panthera pardus) were originally found from southeastern Russia, throughout eastern and southern Asia, the Middle East, North Africa, and throughout subsaharan Africa, in many different habitats, primarily savannahs and forests, but including taiga in parts of Russia and China. In these latter areas, winter temperatures can get down to -12o F (-25o C). Like lions and tigers, leopards can roar.

Snow leopards (Uncia uncia) have always been restricted to mountains in southern and central Asia, including the Altai, Tien Shan, Karakoram and Himalayan ranges among others. They are highly adapted for living in the cold, rocky, mountains, having very thick fur, small ears, short faces, and fur on the bottom of their feet (to act like snowshoes). They also have very long tails, which they use to help keep their balance while chasing prey over rocky, unstable slopes. Although closely related to tigers and leopards, snow leopards cannot roar, due to differences in the anatomy of the larynx (voice box).