Beetle identification - Kakadu NP, NT, Australia
After a hint from @fileunderwater I also think now that it is much more likely that this beetle belongs to the family of the Scarabaeidae which contains some 30.000 species worldwide. Scarabaeidae and Trogidae (what I thought was right before) are part of the same superfamily, the Scarabaeoidea.

The way the antennas are shaped as well as the body shape and the way the legs are ordered looks pretty much like this, even better than for the Trogidae. Have a look at this poster which shows a lot of different varieties (from here):



Some more information and real images can be found here and here.