''Amphistium paradoxum'' (from el, ἀμφί , 'on both sides', el, ιστίον 'sail', and el, παράδοξος 'extraordinary'), the only species classified under the genus ''Amphistium'', is a fossil fish which has been identified as a Paleogene relative of the flatfish, and as a

transitional fossil A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross a ...

. 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. ''Amphistium'' is among the many fossil fish species known from the Monte Bolca ''

Lagerstätte A Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These f ...

'' of

Lutetian The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the ...

Italy. ''

Heteronectes ''Heteronectes chaneti'' is a fossil fish which has been identified as a primitive flatfish, dating to the early Eocene (Lutetian stage) of France. ''Heteronectes'' is reported to be a transitional fossil. In a typical modern flatfish, the head ...

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

References

Transitional fossils Pleuronectiformes Monotypic ray-finned fish genera Prehistoric ray-finned fish genera Eocene fish Fossils of Italy Fossil taxa described in 1835 Taxa named by Louis Agassiz {{Pleuronectiformes-stub