* Mammary glands: This is the most distinctive feature of mammals. Mammary glands produce milk, which is essential for nourishing infant mammals.
* Hair: All mammals have hair, although it may be reduced or absent in some species. Hair helps to insulate mammals and regulate their body temperature.
* Teeth: Mammals have specialized teeth that are adapted for different functions, such as cutting, tearing, and grinding.
* Endothermy: Mammals are endothermic, which means that they can maintain a constant body temperature regardless of the external environment.
* Diaphragm: Mammals have a diaphragm, which is a sheet of muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm helps to move air in and out of the lungs.
* Four-chambered heart: Mammals have a four-chambered heart, which helps to separate oxygenated and deoxygenated blood.
* Neocortex: Mammals have a neocortex, which is a region of the brain that is responsible for higher-level functions such as cognition, language, and abstract thought.
* Live birth: Most mammals give birth to live young, although some species lay eggs.
Additional characteristics of mammals include:
* Vertebrates: Mammals are vertebrates, which means that they have a backbone.
* Bilateral symmetry: Mammals have bilateral symmetry, which means that their bodies can be divided into two mirror-image halves.
* Amniotic eggs: Mammals produce amniotic eggs, which contain a self-contained environment that supports the developing embryo.
* Four limbs: Most mammals have four limbs, although some species have only two limbs or no limbs at all.
* Excretion of urea: Mammals excrete urea, which is a waste product of protein metabolism.
Mammals are the most diverse class of vertebrates, with over 5,000 known species. They can be found in all habitats, from the arctic tundra to the tropical rainforest. Mammals play an important role in many ecosystems, and they provide a variety of benefits to humans, such as food, clothing, and transportation.