Nursing Entrance Exam Practice Test 2025 – Complete Prep Resource

Mammary glands are a distinctive feature that separates mammals from reptiles. These glands produce milk to nourish young mammals, a characteristic vital for the development of offspring during the early stages of their lives. This nurturing aspect is essential for mammalian reproduction, ensuring that young receive the necessary nutrients and antibodies to promote health and growth.

In contrast, while reptiles also have adaptations for reproduction, such as amniotic eggs, they do not possess mammary glands. The other options, such as a four-chambered heart and amniotic eggs, can also be found in various forms in other animal groups, including birds. Feathers for flying is specific to birds and does not apply to mammals. Thus, mammary glands are the definitive characteristic that uniquely identifies mammals within the animal kingdom.