Answer: Naked Mole-Rat

The terms “warm blooded” and “cold blooded” are a bit of a misnomer given that many creatures in both categories can have body temperatures in the same range. But nearly every mammal species on earth engages in some sort of thermoregulatory process to control their body temperature independent of their environment—unlike their distant reptilian relatives. Humans beings, for example, can maintain a stable core body temperature even if their environment is uncomfortably cold, whereas lizards can not. With that in mind, it’s more accurate to refer to “warm blooded” animals as “thermoregulators” and “cold blooded” animals as “thermoconformers”, based on how their body or environment plays a role in their core temperature.

The best known exception to the rule of mammals-as-thermoregulators in the animal kingdom is the naked mole-rat. It is known to be thermoconforming and like “cold blooded” animals, its body temperature is governed not by metabolic processes, but by the temperature of its environment. Instead of altering themselves to change their temperature, naked mole-rats instead engage in the same kind of behaviors you see in other thermoconforming animals: they move to warmer or cooler parts of their burrows and they huddle with or avoid other mole-rats all in a bid to adjust their body temperature.