1. Hair or Fur: Mammals are the only animals that possess hair or fur. This serves multiple functions, including insulation for warmth, protection from the elements, and sensory reception.
2. Mammary Glands: This defining feature gives mammals their name. Female mammals have mammary glands that produce milk to nourish their young. This provides essential nutrition and immunity for the offspring.
3. Three Middle Ear Bones: Mammals have three middle ear bones (malleus, incus, and stapes) that transmit sound vibrations to the inner ear. This allows for a wider range of hearing frequencies and better sound localization.
4. Endothermic Metabolism: Mammals are warm-blooded, meaning they can maintain a relatively constant body temperature regardless of external conditions. This is achieved through a higher metabolic rate and the ability to generate their own heat.
5. Diaphragm: Mammals have a muscular diaphragm that separates the chest cavity from the abdomen. This allows for more efficient breathing and helps control the flow of air into the lungs.
6. Four-Chambered Heart: Unlike most other vertebrates, mammals have a four-chambered heart, which ensures that oxygenated and deoxygenated blood are kept separate, leading to more efficient oxygen delivery to the body.
7. Live Birth: With few exceptions (monotremes), mammals give birth to live young rather than laying eggs. This allows for a longer period of parental care and protection for the offspring.
8. Complex Nervous System: Mammals have a highly developed brain and nervous system, which allows for advanced cognitive abilities, learning, and social behaviors.
9. Specialized Teeth: Mammals have specialized teeth adapted for different diets. This includes incisors for biting, canines for tearing, premolars and molars for grinding, and specialized teeth in certain species for specific functions like filtering food.
10. Sweat Glands: Most mammals have sweat glands that help regulate body temperature by releasing sweat, which evaporates and cools the skin.
It's important to note that there are always exceptions to these general characteristics. For example, some mammals like whales and dolphins have lost their hair, while others like platypuses and echidnas lay eggs instead of giving birth to live young. However, these features overall define the unique and diverse class of mammals.