Final answer:
Endothermy is a beneficial adaptation that gives mammals an edge over reptiles.
Step-by-step explanation:
One beneficial adaptation that gives mammals an edge over reptiles is endothermy, or the ability to regulate body temperature from the inside. This allows mammals to maintain a relatively constant body temperature, which gives them an advantage in diverse environments. Unlike reptiles, which rely on external sources of heat to regulate their body temperature, mammals can adapt to different climates and habitats more effectively.