1. Hair or Fur: All mammals have hair or fur at some point in their lives, even if it's just a very thin coat. This serves for insulation, camouflage, and sensory purposes.
2. Give Birth to Live Young: Mammals are viviparous, meaning they give birth to live young, rather than laying eggs.
3. Mammary Glands: Mammals have mammary glands, which produce milk to nourish their offspring. This is a defining characteristic of the class Mammalia.
4. Warm-Blooded: Mammals are endothermic, meaning they can regulate their own body temperature internally. They are able to maintain a stable temperature regardless of the external environment.
5. Three Middle Ear Bones: Mammals have three middle ear bones (malleus, incus, and stapes) that are responsible for transmitting sound vibrations from the eardrum to the inner ear. This allows for more efficient hearing.