Subclass Metatheria is a group of mammals commonly referred to as marsupials, which includes animals such as kangaroos, koalas, and opossums. These creatures are characterized by their distinctive reproductive physiology, which involves partial development of offspring outside the body of the mother. The term Metatheria serves as a scientific classification for these animals, but there are many synonyms used interchangeably, including marsupialia, Theria, and mammalians. These synonyms refer to the same group of animals and are often used to describe unique physical and behavioral characteristics, including pouches for carrying young and specialized teeth for feeding exclusively on plants or insects.