Amniotes are characterized by which of the following features?

Amniotes are primarily characterized by the presence of an amniotic egg, which is a significant evolutionary adaptation that allows these organisms to reproduce in terrestrial environments. The amniotic egg contains specialized membranes, including the amniotic sac, which provides a protective environment for the developing embryo, allowing it to thrive outside of an aquatic habitat. This adaptation reduces reliance on water bodies for reproduction and development and enables a more efficient use of terrestrial resources.

The amniotic egg is crucial for the survival of the embryo in various environmental conditions, preventing desiccation and allowing for gas exchange, while also providing nourishment through the yolk. This characteristic is a defining feature of amniotes, classifying them into major groups like reptiles, birds, and mammals.