500 Tögrög Diplocaulus

Diplocaulus was a boomerang-skulled amphibian that went extinct roughly 270 million years ago, long before the first dinosaur. Mongolia's numismatic program has leaned heavily into paleontological subjects since the early 2000s, partly because the Gobi Desert remains one of the most productive fossil sites on earth — though Diplocaulus itself is known primarily from Permian deposits in North America, not Central Asia.