In mammals, a monophyletic group, there were a number of different lines living at the same time through the Upper Triassic to the Upper Cretaceous. Each of these lines had a mixture of basal and derived features until, at last, the placental mammals developed the whole suite of derived characters. This gave them a great advantage over the other groups wherever open competition occurred. However, because of their long seclusion in southern continents, some of the monotremes and marsupials have survived.