Money from the sea
The Art Institute of Chicago describes cowrie shells as a currency in Africa, and as shells that were also linked with the spirit world. Imports of cowries rose sharply in the late 15th century. Our files do not say when cowries were first used as money, or where these shells were gathered.
To verify: The Art Institute of Chicago’s own wording on the rise in imports in the late 15th century; Where the shells came from, and when cowries were first used as money in West Africa