250 Francs CFA Mosasaurus

Senegal issues coinage through the Banque Centrale des États de l'Afrique de l'Ouest under the West African CFA franc system, meaning this piece bears Senegalese attribution while monetary policy answers to a regional authority headquartered in Dakar. The CFA franc's fixed peg to the euro — inherited from its earlier peg to the French franc — makes these collector issues a stable-denomination curiosity: the face value is notional, the gold content is the point.

The mosasaurus itself went extinct roughly 66 million years ago at the K-Pg boundary. At 0.5 g of .9999 fine gold, the metal value dwarfs the 250 franc face by a factor of several hundred.