Ekaltadeta ima n. gen. and sp., from freshwater limestones of probable middle Miocene age in northwestern Queensland, is a primitive relative of the Pliocene and Pleistocene species of Propleopus. Three Pleistocene species of Propleopus are recognized: P. oscillans (De Vis, 1888); P. chillagoensis Archer, Bartholomai and Marshall, 1978; and P. wellingtonensis n. sp. Propleopus chillagoensis and P. wellingtonensis, although distinct, are close relatives. Aspects of M2 and probably I1 morphology (judging from the alveolus) indicate that E. ima and the species of Propleopus are monophyletic. The primitive arrangement of the cuspids on the trigonid of M2 and the morphology of the masseteric canal further suggest that the giant rat kangaroos of the genus Propleopus and Ekaltadeta are the plesiomorphic sister group of all other potoroids. Within the current framework of macropodoid systematics (Archer and Bartholomai, 1978; Flannery, 1982), this group requires recognition at the subfamily level. Accordingly, Propleopinae is proposed as a name for the group. It is suggested, on the basis of morphology and examination of wear striae of the premolars, that propleopines may have been omnivores and/or carnivores.