These are Willison-type couplings. Because of the jaw geometry and locking tab, these are less likely to have spontaneous uncoupling events than a traditional knuckle coupler. The traditional knuckle coupler is banned underground in Australia after breakaways on underground grades and Willisons are currently the only permitted coupling for underground use.
They are also widely used in the sugar cane industry in Queensland.
and a second photo showing the under-slung cut lever
Unanderra in oz