Asilid (Robber Fly) with ant prey, HBL ≈18 mm. Wing length 10 mm.
I think these are all the same fly, but I've left it too long to remember clearly. Conioscinella I think.
Also seen on same old wallaby carcass as subsequent observation
Bone-skater fly Piophilidae on long-dead wallaby, The Steppes, Tasmania, March 2020