1. Mammary glands: All mammals have mammary glands that produce milk to nourish their young.
2. Hair: Mammals are characterized by the presence of hair or fur, which helps regulate body temperature and provides insulation.
3. Endothermy (warm-bloodedness): Mammals are endothermic, meaning they can generate their own body heat to maintain a relatively constant body temperature, regardless of the external environment.
4. Four-chambered heart: Mammals possess a four-chambered heart with two atria and two ventricles, allowing for efficient separation and circulation of oxygenated and deoxygenated blood.
5. Diaphragm: Mammals have a muscular diaphragm separating the thoracic cavity from the abdominal cavity, which aids in breathing and ventilation.
6. Specialized teeth: Mammals have specialized teeth adapted for various functions, such as incisors for cutting, canines for tearing, and molars for grinding.
7. Three middle ear bones: Mammals have three small bones (malleus, incus, and stapes) in the middle ear, enhancing hearing sensitivity.
8. Neocortex: The mammalian brain has a well-developed neocortex, which is associated with higher cognitive functions, including language, reasoning, and abstract thinking.
9. Parental care: Mammals generally display parental care, providing nourishment, protection, and nurturing to their offspring until they reach independence.
10. Sweat glands: Most mammals have sweat glands that aid in thermoregulation by releasing sweat, which cools the body through evaporation.
11. Red blood cells: Mammalian red blood cells lack nuclei, allowing for more efficient oxygen transport.
12. Sebaceous glands: Mammals have sebaceous glands that secrete oils to keep the skin and fur moisturized.
13. External ears: Mammals typically have external ear structures called pinnae or auricles, which help collect and direct sound waves.
14. Viviparity: The majority of mammals are viviparous, giving birth to live young rather than laying eggs.
15. Social behavior: Many mammals exhibit social behavior, forming groups or societies with complex interactions and communication systems.