Endothermy As stated previously, mammals are endothermic, a crucial adaptation that has allowed them to be active at any time of the day or night and to colonize severe environments, from deserts to...

Endothermy As stated previously, mammals are endothermic, a crucial adaptation that has allowed them to be active at any time of the day or night and to colonize severe environments, from deserts to ice fi elds. Also, more effi cient blood circulation provided by the fourchambered heart (see chapter 50) and more effi cient respiration provided by the diaphragm (a special sheet of muscles below the rib cage that aids breathing; see chapter 49 ) make possible the higher metabolic rate on which endothermy depends.