Why is a echidna classified as a mammal?

An echidna is classified as a mammal because it possesses key characteristics typical of mammals, such as warm-bloodedness, fur or hair, and the ability to produce milk to nourish its young. Additionally, echidnas belong to a unique group of mammals called monotremes, which lay eggs instead of giving birth to live young, but they still share fundamental mammalian traits. Their anatomical features and reproductive methods distinctly place them within the mammalian class.