A mammal is defined by several key characteristics including the presence of milk-producing mammary glands for feeding their young, having hair or fur, being warm-blooded (endothermic), possessing a unique jaw structure with a single pair of bones, and having three middle ear bones. Mammals are vertebrates, meaning they have a backbone, and typically give birth to live young, though some like monotremes (platypus and echidnas) lay eggs. They also have a more complex brain compared to other animals and use a muscular diaphragm to aid in breathing.
Key Mammalian Traits
- Mammary glands that produce milk for offspring
- Hair or fur on their bodies
- Warm-blooded metabolism, maintaining a steady body temperature
- Three bones in the middle ear aiding in hearing
- Unique lower jaw structure articulated with the skull
- Most give live birth, but some lay eggs (monotremes)
- Larger and more complex brains than other vertebrates
These characteristics distinguish mammals from other vertebrate classes such as reptiles, birds, amphibians, and fish.
Exceptions and Evolution
- Monotremes (platypus, echidnas) lay eggs but still nurse their young with milk.
- Mammals evolved from reptile-like ancestors and now form a distinct class in the animal kingdom called Mammalia, with about 6,640 species described.
In summary, what makes a mammal is a combination of traits focused on milk production, hair, warm-bloodedness, ear bone structure, and their evolutionary lineage.
