When Wild animals are commonly divided into groups with similar characteristics. the two categories used for mammals are what?

Mammals are commonly divided into two main categories: monotremes and therian mammals. Monotremes are egg-laying mammals, such as the platypus and echidna, while therian mammals give birth to live young and are further divided into marsupials (like kangaroos) and eutherians (placental mammals). This classification is based on reproductive strategies and developmental processes.