What it is
Diprotodon optatum was the largest known marsupial, a bulky browser about the size of a rhinoceros. It is extinct. Trackways and bones are common in some Australian Pleistocene deposits.
Range
Much of Pleistocene Australia, in woodland, grassland, and around waterholes.
What happened
Diprotodon is one of the genera that vanish in the ~50,000-40,000-year window after human arrival in Australia. It did not survive to the Last Glacial Maximum. Hunting, fire, and climate are all argued. As with other Sahul megafauna, the honest summary is coincidence with first people plus a climate that was already variable: not a cartoon of total faunal wipeout.
When / status
Extinct about 46,000-40,000 years ago.
Human role
Central in the timing; climate is a discussed co-cause. Neither is a sole proven verdict for every site.
Sources
Roberts et al. 2001; later Diprotodon and Australian megafauna chronologies.