Trituberculata

Trituberculata is an extinct group of animals existing in the fossil record from about 215 – 85 MYA. It contains the ancestors of Placentalia and Marsupialia; all modern mammals except Monotremata are descended from trituberculates. It is named for the three tubercles of the molar teeth. The clade Trituberculata is not always regarded as a valid one, and it likely does not form a monophyletic group. Instead, some of them may be "true" basal mammals, while others may fall just outside the therian crown group.