Mammals are distinguished from other animal classes by several key characteristics, including the presence of mammary glands, which allow females to nurse their young. Mammals also have hair or fur covering their bodies, which aids in insulation and temperature regulation. Additionally, mammals possess three middle ear bones that assist in hearing and a unique type of jaw structure. They are warm-blooded, meaning they can maintain a constant body temperature. Most mammals give live birth, and they have complex brains relative to body size, contributing to their advanced behaviors and social structures.