Miminipossum notioplanetes represents a new Early/Middle Miocene family (Miminipossumidae) of phalangeridan possums recovered from the Two Trees Local Fauna from the Riversleigh World Heritage area in northwestern Queensland and the Kutjamarpu Local Fauna of the Tirari Desert in northern South Australia. Because of widespread convergence in key features of P3 and M1 among phalangeridan families, the interfamilial relationships of Miminipossumidae are uncertain. The age of the Kutjamarpu Local Fauna has been in doubt with estimates ranging from Late Oligocene to Middle Miocene. The new taxon raises to 15 the number of taxa in the Kutjamarpu Local Fauna that are shared with both Riversleigh’s Faunal Zone B (Early Miocene) and Riversleigh’s Faunal Zone C (Middle Miocene) assemblages. Although there is relatively little biocorrelative support for the estimate of a Late Oligocene age, doubt remains about whether the age is more likely to be Early or Middle Miocene. In terms of palaeoenvironmental implications, because both Riversleigh’s Early and Middle Miocene assemblages have been concluded to have accumulated in temperate, wet, species- rich lowland forests, the same or similar Early/Middle Miocene palaeoenvironments may well have extended into central Australia at the time when the Kutjamarpu assemblage was accumulating.