Animals of cold areas possess thick coat of hair, scales, feathers and subcutaneous fat (Gloger's rule). Warm blooded animals (birds, mammals) of colder areas are of larger size as compared to those of warmer areas (Bergmann's rule). Extremities of mammals (ears, snout, tail, legs) of colder areas are shorter than those of warmer regions (Allen's rule). Birds have narrow wings in cold areas as compared to those of warmer regions (Rensch's rule). Fish of colder waters tend to have more vertebrae (Jordan's rule).