* They give birth to live young. Koalas don't lay eggs like reptiles or birds.
* They nurse their young with milk. Koalas have mammary glands and produce milk to nourish their offspring.
* They have fur. Koalas are covered in a thick coat of fur for insulation.
* They are warm-blooded. Koalas maintain a constant internal body temperature, unlike reptiles which are cold-blooded.
* They breathe air with lungs. Like all mammals, koalas use lungs to obtain oxygen.
While koalas may seem different from other mammals at times (they are often mistaken for bears!), they belong firmly in the mammal category due to these fundamental characteristics.