No, reptiles are not mammals. They are a separate category of animal altogether. Reptiles are characterized by their scaly skin, which is an adaptation to life on land that helps them regulate their body temperature and prevent water loss. Most reptiles lay eggs, although some give birth to live young. Additionally, reptiles typically have cold-blooded metabolisms, meaning that they cannot generate their own body heat and must rely on external sources of warmth to maintain their body temperature.