Joculusium muizoni is a fossil species of dasyuromorph, an order of marsupials represented in the modernAustralian fauna by the quolls, Tasmanian devil and recently extinct thylacine. When discovered, the specimen exhibited the least derived characteristics of the known species of the order that was found in dasyurid and thylacinid families. The only specimen is a jaw bone of a carnivore that probably ate smaller vertebrate species or insects.