1. Hair or Fur: This is arguably the most defining feature of mammals. They are the only animals that possess hair or fur, which serves various functions like insulation, camouflage, and sensory perception.
2. Mammary Glands: Mammals are named after their mammary glands, which produce milk to nourish their offspring. This is a key characteristic that sets them apart from other animal groups.
3. Endothermy: Mammals are warm-blooded, meaning they can regulate their own body temperature internally. This allows them to thrive in a wider range of environments compared to cold-blooded animals.
4. Three Middle Ear Bones: Mammals have three tiny bones in their middle ear (malleus, incus, and stapes) that transmit sound vibrations from the eardrum to the inner ear. This highly developed auditory system contributes to their excellent hearing ability.
5. Four-Chambered Heart: All mammals have a four-chambered heart that efficiently separates oxygenated and deoxygenated blood, allowing for a high metabolic rate and sustained activity.
6. Diaphragm: This muscular sheet separates the chest cavity from the abdomen and plays a crucial role in breathing.
7. Specialized Teeth: Mammals typically have heterodont dentition, meaning they possess different types of teeth (incisors, canines, premolars, molars) adapted for specific functions like biting, tearing, and grinding.
8. Neocortex: The mammalian brain possesses a highly developed neocortex, responsible for complex functions like learning, memory, and higher cognitive abilities.
9. Live Birth: While a few exceptions exist like the platypus and echidnas, most mammals give birth to live young rather than laying eggs.
10. Parental Care: Mammals typically exhibit a high level of parental care, nurturing and protecting their offspring until they are relatively independent.
It's important to note that while these characteristics are generally true for mammals, there can be exceptions within the diverse range of species. For instance, some aquatic mammals like whales and dolphins have lost their hair, and some primitive mammals like echidnas lay eggs.