Answer
Current evidence suggests that endothermy evolved twice among animals. The first time occurred in the lineage of reptiles and dinosaurs that eventually led to the birds. The second time is in the lineage that led to the mammals.
Work Step by Step
Current evidence suggests that endothermy evolved twice among animals. The first time occurred in the lineage of reptiles and dinosaurs that eventually led to the birds. The second time is in the lineage that led to the mammals. Therefore, both birds and mammals are endothermic, but the lineages are only distantly related to one another.
