Amphistium paradoxum (from Greek: ἀμφί amphi, 'on both sides', Greek: ιστίον istion 'sail', and Greek: παράδοξος paradoxus 'extraordinary'),[1] the only species classified under the genus Amphistium and the family Amphistiidae, is a fossil fish which has been identified as a Paleogene relative of the flatfish, and as a transitional fossil.

[3] Amphistium is among the many fossil fish species known from the Monte Bolca Lagerstätte of Ypresian Italy.

Heteronectes is a related, and very similar fossil from a slightly earlier strata of France.

Heteronectes is sometimes also placed in the family Amphistiidae, though other studies find it to be more basal than any other flatfish taxon.

This article about a prehistoric ray-finned fish is a stub.