A new Miocene smelt fish, Spirinchus izumoensis sp. nov. (Osmeriformes, Osmeridae) from Hiebara in Izumo, Shimane, Japan

Abstract

A new smelt fish, Spirinchus izumoensis sp. nov., is described from the Lower to Middle Miocene Kawai Formation in Shimane, southwestern Japan. The new species differs from its congeners in possessing the unique combination of the following characteristics: enlarged and thickened anal fin rays and enlarged anterior proximal pterygiophores; non-parallel anterior half proximal pterygiophores and parallel posterior proximal pterygiophores of the anal fin; short proximal pterygiophores at the middle part of the anal fin, almost as short as or shorter than their associated haemal spines; and total of 48 vertebrae. The new species was found along bedding planes with well-developed lamination, suggesting that it was deposited under low-oxygen bottom-water conditions. It is inferred that a brackish estuarine environment influenced by both freshwater and marine conditions prevailed during the deposition of mudstone in the Kawai Formation.

ZooBank registration: urn:lsid:zoobank.org:act:CA1A427E-7EFE-438B-B1F9-D5E68F479395