Subclass of the class Mammalia, including those mammals that give birth to live young. This taxon includes all extant mammals except the egg laying Monotremata.
Therian mammals are divided into 2 extant infraclasses: Metatheria (the marsupials) with 4 orders, and Eutheria (the placentals) with 17 orders. They range through all faunal regions and all oceans.
(after DeBlase, 1982)