Trituberculata

The Trituberculata is an extinct group of mammals in the fossil record from about 215–85 illion years ago (mya). The discoveries were isolated teeth, so not much else can be said about the animals. They were small insectivores, and probably nocturnal. The group contains the ancestors of Placentalia and Marsupialia; all modern mammals except Monotremes are descended from trituberculates.
The name comes from the three tubercles (cusps) of the molar teeth (not to be confused with Triconodonta). The clade Trituberculata is not always regarded as valid. They probably do not form a monophyletic group. Instead, some may be "true" basal mammals (though not always closest related to each other). Others (such as the symmetrodonts) may fall just outside the therian crown group.