Mammals are the largest class in the animal world. Mammals are of different types and can be distinguished up into marine mammals, smaller mammals and larger mammals. Mammals belong to the class mammalia.
Since mammals are of different types they are classified into three subclass based on their reproduction. They are Eutheria, Metatheria and Prototheria.
Mammals that give birth to their young ones directly belong to the subclass Eutheria. The young ones form as an embryo in the mother stomach and grow there for a certain period of time. This subclass consists of 19 orders. Best example and well known of this class are humans, dogs and cats.
Mammals that belong to this subclass also give birth to their young ones but the young ones are born immature. So they jump into their mother pouch and stay their till they are mature. Metatheria subclass contains seven orders with 250 species. Marsupials and kangaroo are the best example for this subclass.
Prototheria consists of egg laying animals and are also known as monotremes. This subclass consists of six species all in one order.
Although mammals are classified in to class, subclass, and order the scientist have classified on the general basis. This general classification makes it easy to learn about the mammals class and their distinguished features.