Also because of the higher metabolism to maintain a higher temperature an insulation is required to conserve the heat. Mammals generate the internal heat via metabolism. More insulation and a countercurrent heat-exchanger . For terrestrial vertebrates, it is more highly developed in mammals. It is used to detect enemies, find mates, mark territories, and find food.
Olfaction is used much in the sometimes highly social activities of mammals.
Mammals are the most intelligent also. Birds are best, especially the parrots and crow family. Mammals can hear well, because of the 3 middle ear bones mentioned above. Dogs have acute hearing. These species bounce a sound wave off an object.