1. They give birth to live young: Blue whales are viviparous, meaning they give birth to live offspring that develop inside the mother's body. This is a defining characteristic of mammals.
2. They nurse their young with milk: Blue whales, like all mammals, produce milk to feed their calves. This milk provides essential nutrients and antibodies for the young whale's growth and development.
3. They have hair (although it may be reduced): While blue whales have very little hair, they do possess hair follicles, a characteristic of mammals.
4. They are warm-blooded: Blue whales, unlike reptiles or fish, maintain a stable internal body temperature regardless of the external environment. This is crucial for their survival in various climates.
5. They breathe air: Blue whales, like all mammals, have lungs and must breathe air at the surface. This distinguishes them from fish, which breathe through gills.
6. They possess a four-chambered heart: Mammalian hearts are more efficient than the two- or three-chambered hearts found in other vertebrates. This allows for a more efficient delivery of oxygen to the body.
7. They have a diaphragm: The diaphragm is a muscular structure that plays a crucial role in breathing. This is a defining characteristic of mammals.
8. They possess a complex nervous system: Mammals have a highly developed brain and nervous system that enables them to learn, communicate, and navigate their environment effectively.
These characteristics clearly demonstrate that blue whales share the fundamental traits that classify animals as mammals. Their adaptation to an aquatic environment doesn't negate their fundamental mammalian nature.