Invertebrates, fishes, reptiles, and amphibians are generally ectotherms. In contrast, animals that derive most of their body heat from their own metabolism are called endotherms. Many lizards, which are ectotherms , have active body temperatures higher than those of mammals. Note again that the terms ectotherm and endotherm are not based on the animals' body temperature, but rather on the main source of body heat. Reptiles are generally ectotherms with relatively low metabolic rates that contribute little to the normal body temperature.
Reptiles warm themselves mainly by behavioural adaptation.
They seek warm places, orienting toward heat sources to increase heat uptake and expanding the body surface exposed to a heat source. For amphibians, the optimal temperature range varies substantially with species.