Mammals are a diverse group of animals that share several distinguishing characteristics, which separate them from other animal groups. These characteristics include:

1. Hair or Fur:
Mammals are the only group of animals that have hair or fur covering their bodies at some point in their life. Hair provides insulation, protection, and sensory functions. This unique feature helps mammals regulate their body temperature and adapt to various environments.

2. Mammary Glands:
Mammals possess specialized glands called mammary glands, which produce milk to nourish their young. The ability to nurse offspring with milk is a defining characteristic of mammals and allows for the development of a strong parent-offspring bond.

3. Endothermy:
Mammals are endothermic, meaning they can generate and maintain their own body heat. This ability allows mammals to survive in a wide range of habitats and climates. Endothermy is especially advantageous for mammals that live in colder environments, as it enables them to maintain a constant internal body temperature.

4. Four-Chambered Heart:
Mammals have a four-chambered heart, which allows for efficient circulation of oxygenated and deoxygenated blood. This adaptation ensures that oxygen-rich blood is delivered to the tissues and organs, supporting their metabolic needs.

5. Diaphragm:
Mammals possess a muscular structure called the diaphragm, which aids in respiration. The diaphragm helps to expand and contract the lungs, facilitating the intake of oxygen and the expulsion of carbon dioxide.

6. Specialized Teeth:
Mammals have a diverse range of teeth adapted to their specific dietary needs. These teeth include incisors, canines, premolars, and molars. Different mammalian species have varying tooth structures, allowing them to eat a variety of foods such as meat, plants, or a combination of both.

7. Well-Developed Brain:
Mammals have a highly developed brain compared to other animal groups. This complex organ enables mammals to exhibit a wide range of behaviors, adapt to their environment, and learn from experiences.

8. Viviparity:
Most mammals give birth to live young, a reproductive strategy known as viviparity. This allows for parental care and protection of offspring, increasing their chances of survival.

In conclusion, mammals possess a unique set of characteristics including hair or fur, mammary glands, endothermy, a four-chambered heart, a diaphragm, specialized teeth, a well-developed brain, and viviparity. These traits distinguish them from other animal groups and have contributed to their remarkable diversity and success in various ecosystems.