Amphistium paradoxum (from Greek: ἀμφίamphi, 'on both sides', Greek: ιστίονistion 'sail', and Greek: παράδοξοςparadoxus '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.[2] In a typical modern flatfish, the head is asymmetric with both eyes on one side of the head. In Amphistium, the transition from the typical symmetric head of a vertebrate is incomplete, with one eye placed near the top of the head.[3]
Amphistium is among the many fossil fish species known from the Monte BolcaLagerstätteofYpresian 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.[4][5]
