1) Mammary glands: Female mammals possess mammary glands, which are specialized glands that produce milk to nourish their young. This unique characteristic enables mammals to provide a nutritious and easily digestible food source for their offspring.
2) Hair: Mammals are distinguished by the presence of hair or fur, which provides insulation and protection from the environment. The type, density, and colour of hair vary among different mammal species, contributing to their diverse appearances.
3) Three middle ear bones: Mammals have three small bones in their middle ear, known as the malleus, incus, and stapes, which enhance sound transmission and improve hearing sensitivity. This feature contributes to the advanced auditory capabilities of mammals.
4) Four-chambered heart: Mammals possess a unique circulatory system with a four-chambered heart. The separation of the heart into distinct chambers allows for efficient circulation and oxygenation of blood, enabling mammals to sustain higher metabolic rates and maintain a constant body temperature. These four features collectively define the class Mammalia and distinguish mammals from other animal groups.