There are three major groups of mammals, categorized on the basis of their see concept 34.6 ( page 739)

There are three major groups of mammals, categorized on the basis of their method of reproduction. Monotremes lay eggs to have children instead of having the mother bear them. The second type of mammal is the marsupial, which are non-placental animals who carry their young in their pouches. Eutherians are the third group who are placental mammals.

C14 dating since carbon is present in both living and no living objects .