Fossil Mooneyes (Teleostei: Hiodontiformes, Hiodontidae) from the Eocene of western North America, with a reassessment of their taxonomy

The skeletal anatomy of fossil hiodontids from western North America is examined based on newly-prepared specimens, including several specimens that were prepared using the acid transfer method and some using the ‘lost fossil’ technique. This study resulted in many new interpretations and clarifications, such as the presence of a curved tubular nasal bone and a posterodorsal spine on the opercle of ‘† Eohiodon ’, as found in extant Hiodon . We also further describe the variation of the caudal skeleton that has been known in both fossil and extant Hiodon . For instance, the neural spine of preural one is most often fully developed (as it is in a minority of extant Hiodon specimens), although in some specimens it is rudimentary, as it is in most specimens of living taxa. We review the characters that have been used in recent analyses of relationships of osteoglossomorph fishes. After correcting the descriptions of the fossil taxa, we could find no valid synapomorphies to separate the genus † Eohiodon from the genus Hiodon . Therefore, we conclude that † Eohiodon should be regarded as a synonym of Hiodon .