Order that includes the earliest of all mammals, living from the late Triassic until the early Cretaceous and distributed over the northern continents. Typically the molar teeth each had a row of three sharp conical cusps, the teeth of the upper and lower jaws forming a shearing device. Premolars and molars were differentiated, probably with some replacement, and probably the young were fed on milk secreted by the mothers. Triconodonta may have been homoiotherms and nocturnal, and possibly they were arboreal. They are believed to have been true carnivores rather than insectivores. Triconodon, one of the larger forms, from the Upper Jurassic, was the size of a modern cat. The order is believed to have evolved from therapsids independently of the main line of mammalian evolution and to have left no descendants.