The primary characteristic of reptiles is their scaly skin, which is adapted to prevent water loss in terrestrial environments. Reptiles, including snakes, lizards, turtles, and crocodiles, possess skin covered in scales made of keratin, a tough protein. This adaptation allows them to thrive in various habitats by conserving moisture and providing protection against environmental elements and predators. Additionally, reptiles are ectothermic, meaning they rely on external sources to regulate their body temperature. Other features include laying eggs with protective shells or giving live birth, and their lungs enable them to respire effectively.