Presence of hair and mammary glands are a diagnostic feature of which class of kingdom Animalia?

The presence of hair and mammary glands is a defining characteristic of the class Mammalia within the kingdom Animalia. Mammals are the only group of animals that have evolved hair, which serves various functions including insulation, camouflage, and sensory perception. Additionally, mammary glands are unique to mammals, as they provide milk to nourish their young, which is a critical feature in the reproductive process and survival of offspring.

In contrast, the other classes listed do not exhibit these features. Reptilia includes animals such as snakes and lizards, which possess scales instead of hair and do not have mammary glands. Aves, or birds, have feathers, which serve a similar purpose to hair but are distinct in structure and function, and they also lack mammary glands. Amphibia refers to frogs and salamanders, which have moist skin for respiration and reproduction but do not have hair or mammary glands. Thus, the correct answer centers on the unique traits of Mammalia that distinguish it from the other animal classes mentioned.