This set is a PNC version of the four-coin "privy mark" set featuring Australian dinosaurs. The PNC has four themed postage stamps also featuring the dinosaurs.
The Mint says about the set:
"Beautifully designed and privy marked, this four-coin collection encapsulates a slice of Australia’s dinosaur history dating back to the Cretaceous Period - an epic 145 million to 66 million years ago! While the dinosaurs’ names are quite a mouthful, you’re bound to recognise Australia’s best-known sauropod, Diamantinasaurus matildae, which was a whopping 16 to 20 metres long, or maybe the Kunbarrasaurus ieversi, which was covered in bony armour. Skeletons of both these species have been found in Queensland, along with the carnivorous and frightening-looking Australovenator wintonensis. Completing the collection is the elaphrosaurine theropod, which was discovered in Victoria and thought to enjoy a plant-based diet. Each coin gives a nod to the creatures that inhabited Australia long before we did and will no doubt be a catalyst for much discussion as collectors discover more about these magnificent animals."
The four dinosaur coins in the set have different privy marks, one letter each, which spell DINO when placed next to each other.