Here are some key characteristics of mammals:
* Warm-blooded: They maintain a constant internal body temperature.
* Hair or fur: This provides insulation and helps regulate body temperature.
* Give birth to live young: Most mammals are viviparous, meaning they give birth to live offspring.
* Nurse their young: They produce milk to nourish their young.
* Have a more complex brain than other vertebrates. This allows for advanced learning and behavior.
Mammals are a diverse group that includes everything from tiny shrews to massive whales.