New perspective on the origin of endothermy

A new hypothesis for the origin of endothermy in birds is discussed. I suggest extensive parental care provided the initial impetus for the evolution of endothermy. Among extant animals one of the most important functions of an endothermic metabolism is the incubation of embryos. Furthermore, I propose that extensive parental care is a key innovation that greatly influenced much of the homoplasy observed in extant birds and mammals, including their extraordinary ability to sustain vigorous exercise and their parasagittal postures.