http://www.dictionary.com/search?q=marsupial
Sticking to the Mammal in context, I think “marsupial” is not well defined here, and I was looking for a better source, but thought it would be more fun to ask you people.
If you consider the definitions for “monotreme”, you get an idea of the baby in it’s smallest form, and of how it is made. The same thing goes for “placental”. But not “marsupial”. Anyone here even care? I hope so.