Diprotodon
Diprotodon was the largest marsupial that ever lived, or at any rate, the heaviest. Its family, the Diprotodontidae, existed from at least 1.6 million years ago until extinction some 40,000 years ago. So it lived through most of the Pleistocene epoch. Its forebears lived in the  late Oligocene to early Miocene roughly 23 million years ago.