What really makes an animal warm-blooded?

It’s mainly due to brown adipose tissue, whose primary purpose is thermoregulation. What distinguishes this type of fat is the greater amount of mitochondria that dissipate heat per cell, compared to white fat used as reserve.

Although this is the main cause, homeothermia is nevertheless a complex phenomenon that is part of a web of numerous other factors.

There have even been mammals that have lost this characteristic, such as the Balearic cave goat, which lived in the Balearic Islands until its extinction due to man, around 5000 years ago.

The goat, in order to survive the lack of food due to frequent droughts, developed a slow metabolism like that of an ectotherm. This has been deduced from the lamellar structure of its bones, more similar to that of a crocodile than a goat, which reveals a slow and unsteady growth of the organism, like today’s reptiles.