Endotherm

Examples include special-function muscular exertion such as shivering, and uncoupled oxidative metabolism, such as within brown adipose tissue.

However, Argentine black and white tegu, leatherback sea turtles, lamnid sharks, tuna and billfishes, cicadas, and winter moths are mesothermic.

One recent study claimed the origin of endothermy within Synapsida (the mammalian lineage) was among Mammaliamorpha, a node calibrated during the Late Triassic period, about 233 million years ago.

In many endothermic animals, a controlled temporary state of hypothermia conserves energy by permitting the body temperature to drop nearly to ambient levels.

The body temperatures of many small birds (e.g. hummingbirds) and small mammals (e.g. tenrecs) fall dramatically during daily inactivity, such as nightly in diurnal animals or during the day in nocturnal animals, thus reducing the energy cost of maintaining body temperature.

There may be other variations in temperature, usually smaller, either endogenous or in response to external circumstances or vigorous exertion, and either an increase or a drop.

[7] The resting human body generates about two-thirds of its heat through metabolism in internal organs in the thorax and abdomen, as well as in the brain.

[8] Heat loss is a major threat to smaller creatures, as they have a larger ratio of surface area to volume.

Aquatic warm-blooded animals, such as seals, generally have deep layers of blubber under the skin and any pelage (fur) that they might have; both contribute to their insulation.

Birds, especially waders, often have very well-developed heat exchange mechanisms in their legs—those in the legs of emperor penguins are part of the adaptations that enable them to spend months on Antarctic winter ice.

While tens of thousands of fungal species infect insects, only a few hundred target mammals, and often only those with a compromised immune system.

Because ectotherms depend on environmental conditions for body temperature regulation, they typically are more sluggish at night and in the morning when they emerge from their shelters to heat up in the first sunlight.

[15] It is thought that the evolution of endothermia was crucial in the development of eutherian mammalian species diversity in the Mesozoic period.

Endothermia gave the early mammals the capacity to be active during nighttime while maintaining small body sizes.

[17] The honey bee, for example, does so by contracting antagonistic flight muscles without moving its wings (see insect thermoregulation).