The evolution of nasal turbinates and mammalian endothermy

Complex nasal turbinal bones are associated with reduction of respiratory water loss in desert mammals and have previously been described as an adaptation to xeric conditions. However, complex turbinates are found in virtually all mammals. Experimental data presented here indicate that turbinates also substantially reduce respiratory water loss in five species of small mammals from relatively mesic environments. The data support the conclusion that turbinates did not evolve primarily as an adaptation to particular environmental conditions, but in relation to high ventilation rates, typical of all mammals. Complex turbinates appear to be an ancient attribute of mammals and may have originated among the therapsid ancestors of mammals, in relation to elevated ventilation rates and the evolution of endothermy.