It is quite mind blowing that this is polyphyletic on mammals and birds, what can't parallel evolution achieve??
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Homeothermy refers to the ability of an organism to maintain a constant internal body temperature regardless of external environmental conditions. This thermoregulation is a characteristic of many mammals and birds, which are often referred to as "endotherms." Homeothermic organisms have sophisticated physiological mechanisms that allow them to generate and conserve heat, enabling them to remain active in a wider range of environmental temperatures.