Final answer:
The characteristic that distinguishes amphibians from all living reptiles is that they lay anamniotic eggs.
Step-by-step explanation:
The characteristic of amphibians that distinguishes them from all living reptiles is that they lay anamniotic eggs. Unlike reptiles, birds, and mammals, amphibians do not produce amniotic eggs, which means they must lay their eggs in water to prevent them from drying out. Their eggs are usually covered in a jelly-like substance that helps keep them moist and offers some protection from predators.