Reptiles are scaly animals that live in warm areas and eat plants or small animals. There are several types of reptiles including lizards, snakes, crocodilians, turtles, and tortoises. Reptiles are ectothermic, meaning they rely on external heat sources like sunlight to regulate their body temperature. While dinosaurs were the largest reptiles to ever live, modern reptiles have diversified to fill ecological niches through evolution from a common ancestor.