1. Mammary glands: This is the defining feature of mammals. Female mammals produce milk to nourish their young.
2. Hair or fur: All mammals have some form of hair or fur, even if it is very sparse. It provides insulation, protection, and can be used for sensory purposes.
3. Three middle ear bones: Mammals have three tiny bones in their middle ear: the malleus, incus, and stapes. This unique structure allows for more sensitive hearing.
4. Warm-blooded: Mammals are endothermic, meaning they regulate their own body temperature internally. This allows them to be active in a wide range of environments.
5. Four-chambered heart: The heart of a mammal has four chambers, which allows for efficient oxygen delivery to the body.
6. Diaphragm: Mammals have a diaphragm, a muscular sheet that separates the chest cavity from the abdominal cavity. This allows for efficient breathing.
7. Live birth: Most mammals give birth to live young, although a few, like the platypus and echidnas, lay eggs.
8. Specialized teeth: Most mammals have specialized teeth for different functions, such as cutting, tearing, and grinding food.
9. Large brain size: Mammals have larger brains relative to body size compared to other vertebrates. This allows for complex behaviors and learning abilities.
10. Nerve endings in skin: Mammals have highly sensitive nerve endings in their skin, allowing them to feel touch, pressure, and temperature.
These shared characteristics reflect the evolutionary history of mammals and demonstrate the success of this diverse group of animals.