Fontannesia is an ammonoid cephalopod genus with a small to medium size, evolute, discoidal shell that was extant during the Jurassic Period.

The sides are ribbed, the venter has a single median keel, and tubercles are lacking.

Fontannesia is included in the Sonniniidae (Hildoceratoidea) and has been found widespread in Europe, western Australia, Canada, and Argentina.

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