Classification
Domain: Eukaryotes
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Subclass: Prototheria (monotremes: egg-laying mammals)
Subclass: Theria (live-bearing)
    Infraclass: Metatheria (marupials: mammals with a pouch. They are born with little development) 
                     Eutheria (placentals: females have a placenta to nourish their young)