1. Hair or Fur: This is the most obvious defining characteristic. Hair provides insulation, helps with camouflage, and aids in sensory perception.
2. Mammary Glands: Mammals are named for these glands, which produce milk to nourish their young. This allows for a prolonged period of parental care and development.
3. Endothermy: Mammals are warm-blooded, meaning they can regulate their own body temperature internally. This allows them to be active in a wider range of environments.
4. Three Middle Ear Bones: Mammals have three tiny bones (malleus, incus, and stapes) in their middle ear that amplify sound. This allows for a greater range of hearing compared to other vertebrates.
5. Diaphragm: Mammals have a muscular diaphragm that helps with breathing. It separates the chest cavity from the abdominal cavity and aids in efficient oxygen intake.
6. Specialized Teeth: Mammals typically have specialized teeth (incisors, canines, premolars, and molars) adapted for different diets. This is a reflection of the diverse range of feeding habits seen in mammals.
7. Four-chambered Heart: Mammals have a fully developed four-chambered heart that separates oxygenated and deoxygenated blood. This allows for efficient delivery of oxygen to the body.
8. Larger Brain Size: Compared to other vertebrates, mammals have a relatively larger brain size. This is associated with complex behaviors, intelligence, and learning abilities.
9. Live Birth: Most mammals give birth to live young, though some lay eggs (monotremes). This allows for greater parental care and protection during development.
10. Highly Developed Nervous System: Mammals have a sophisticated nervous system, leading to complex communication, social interactions, and advanced cognitive abilities.
These characteristics, taken together, define mammals as a distinct and successful group of vertebrates.