1. Mammary Glands: The most obvious feature! Mammals are named for their mammary glands, which produce milk to nourish their young.
2. Hair or Fur: All mammals have hair or fur at some point in their lives. This serves as insulation, camouflage, and sensory functions.
3. Three Middle Ear Bones: Mammals have three bones in their middle ear (malleus, incus, and stapes), which allow for a greater range of sound perception compared to other vertebrates.
4. Warm-bloodedness (Endothermy): Mammals regulate their own internal body temperature, maintaining a constant core temperature, which allows them to be active in a wider range of environments.
5. Give Birth to Live Young: Almost all mammals give birth to live young, with the exception of the monotremes (platypus and echidnas) which lay eggs.
6. Diaphragm: Mammals have a diaphragm, a muscle that separates the chest cavity from the abdominal cavity, which aids in breathing.
7. Four-chambered Heart: Mammals possess a four-chambered heart, allowing for more efficient oxygen transport throughout the body.
8. Specialized Teeth: Mammals have different types of teeth (incisors, canines, premolars, and molars) adapted for their specific diets.
9. Larger Brain Size: Compared to other vertebrates, mammals have a larger brain size relative to their body size, which allows for more complex behavior and intelligence.
10. Sweat Glands: Most mammals have sweat glands, which help in regulating body temperature.
These characteristics, shared by all mammals, including humans, prove our membership in this diverse and fascinating group.