A long-bodied centriscoid fish from the basal Eocene of Kabardino-Balkaria, northern Caucasus, Russia

The Paleocene-Eocene transition is of crucial interest for interpreting the Cenozoic evolutionary radiation of vertebrates. A substantial increase of the number of vertebrate families occurred between the Late Paleocene and Early Eocene, with the appearance of most of the representatives of extant lineages. Basal Eocene marine fish diversity is currently poorly known, exclusively restricted to two assemblages from Denmark and Turkmenistan, respectively. Exceptionally well-preserved articulated skeletal remains of fishes have recently been discovered from a basal Eocene sapropelitic layer exposed along the Kheu River in the Republic of Kabardino-Balkaria, northern Caucasus, Russia. Here, we report on gen. et sp. nov., a new peculiar syngnathoid fish from this new Ciscaucasian locality. The morphological structure of the single available specimen suggests that it is the first long-bodied member of the superfamily Centriscoidea, representing the sole member of the new family Gerpegezhidae, which forms a sister pair with the extant family Centriscidae.