Neogene Deep-sea Smelts (Argentiniformes: Microstomatidae) from the Far East Russia

Abstract

Deep-sea smelts (Argentiniformes: Microstomatidae, Bathylaginae) from the Miocene of Far East Russia (Sakhalin and Urup islands) are described. The specimens described belong to four taxa, one of which is assigned to a new species of the genus Leuroglossus. Like Recent smoothtongues, the new species has thickened medial rays in the caudal fin. The small number of abdominal vertebrae makes the new species similar to the extant southern smoothtongue L. stilbius, which occurs along the eastern coasts of the Pacific Ocean. The new species differs from extant smoothtongues in the short snout, which is not longer than the orbit. Phylogenetic analysis of morphological features of the new species, using a matrix of characters of living deepsea smelts, shows that it occupies a basal position in the genus Leuroglossus. Three other extinct taxa cannot be reliably classified below the level of the subfamily Bathylaginae or tribe Bathylagini because of insufficient preservation of available specimens. The new records of deep-sea smelts in Far East Russia show that this fish subfamily was widespread and highly morphologically differentiated in the Neogene.