At the heart of the high fitness of birds and mammals are changes in the structure of their bodies (complete separation of arterial and venous blood flow due to the presence of a four-chambered heart and the loss of one aortic arch; the development of feather or hair cover, which contributes to the preservation of heat, the development of the brain, which provides the possibility of perfect regulation of metabolism, circulation, etc.).
There are many smaller private devices that ensure the constancy of body temperature in homeothermic animals. For example, in pinnipeds and whales, a thick layer of fat in the subcutaneous tissue contributes to keeping warm.
In most birds, the body temperature is +41 – +43 ° С, and in mammals – +35 – +38 ° С.
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