* Mammary glands: All mammals have mammary glands, which produce milk to nourish their young.
* Hair: Most mammals have hair or fur, which helps to insulate them and keep them warm.
* Three middle ear bones: Mammals have three bones in their middle ear (the malleus, incus, and stapes), which help to amplify sound waves.
* A four-chambered heart: Mammals have a four-chambered heart with two atria (upper chambers) and two ventricles (lower chambers). This allows for more efficient circulation of blood.
* Warm-bloodedness: Mammals are warm-blooded (endothermic), meaning that they can maintain a constant body temperature regardless of the external environment.
* Parental care: Most mammals provide some form of parental care for their young, including feeding, protecting, and teaching them how to survive.
Additional Characteristics
In addition to these key characteristics, mammals also have a number of other features that distinguish them from other animals. These include:
* A complex brain: Mammals have a highly developed brain, which allows for a wide range of cognitive abilities, including learning, memory, and problem-solving.
* A diaphragm: Mammals have a diaphragm, a sheet of muscle that separates the thoracic cavity from the abdominal cavity. This muscle helps mammals breathe by contracting and relaxing, drawing air in and out of the lungs.
* Teeth: Most mammals have teeth, which they use for a variety of purposes, including eating, defense, and grooming.
* Opposable thumbs: Many mammals have opposable thumbs, which allow them to grip objects and perform a wide variety of tasks.
Mammals are a diverse group of animals, with over 5,000 known species. They can be found in a wide variety of habitats, from the tropics to the poles, and from the sea to the mountains. Mammals play an important role in many ecosystems, and they have a special relationship with humans, who are also mammals.