A the allometric coefficient a (mlO2/h) in different groups, is formulated by recalculating the equations and transforming with a common average b = 0.7248, depending on the geological time of divergence of the clades B BMR ratio in the six principal groups of endothermic animals are expressed in relation to BMR of Passeriformes (a non-dimensional coefficient of the intercept), dependent on the time of appearance in evolution.