Revision of the American otolith-based fish species described by Koken in 1888

Nineteen of the 23 species described by Koken (1888) from the U.S. Gulf Coast Paleogene are considered to be valid. The four remaining ones proved to be based on eroded or juvenile otoliths lacking diagnostic features to define a species. Two of them, however, are identifiable at generic level and represent Recent genera (Centroberyx and Pterothrissus) that do not occur in the present-day American seas. The two others, Otolithus (Sparidarum) insuetus and Otolithus (Sciaenidarum) similes are based on badly preserved non-diagnostic otoliths. Some of Kokens series of syntypes proved to be mixtures containing additional species: the syntypes of Paraconger sector also include specimens of Ariosoma nonsector Nolf & Stringer, 2003; those of Aplodinotus gemma include "genus Sciaenidarum" radians Koken, 1888 and Sciama pseudoradians (Dante & Frizzell, 1965). A new species, Apiodinotus distortus, is described because it occurs together with the former three sciaenid species in the same sample of the Byram Marl. By evaluating the generic affinities of the sciaenid species described by Koken (and of other Paleogene sciaenids), it was discovered that many of them have their closest relationships to present-day sciaenids with a freshwater habitat. They are considered to be descendants of marine ancestors that survive today in freshwater. These successful Paleogene marine sciaenid taxa (Apiodinotus, Pachyurinae) were probably replaced in the marine environment by successful modern groups (Cynoscioninae, Micropogoninae, and Lariminae) that have no Paleogene fossil record but are known since the Miocene