My reference: "A Field Guide to the Mammals of Australia" by Peter Menkhorst and Frank Knight.
Rattus lutreolus - Diurnal, vegetarian (eats mostly stems of grass and sedges), forms runways through dense vegetation and extensive shallow burrow systems.
Tail is relatively short - clearly less than the body length. It is naked and uniformly dark grey or blackish, with obvious scale rings - A bush rat (Rattus fuscipes) has a longer pinkish tail:
Small, dark grey, rounded ears:
Fur of upper parts is long and dense. Colour varies from reddish brown through chocolate to blackish:
