The karyotype of the Amu Darya sturgeon, Pseudoscaphirhynchus kaufmanni (Actinopterygii: Acipenseriformes: Acipenseridae)

Abstract

The order Acipenseriformes is an ancient group of vertebrate animals represented by two fossil families: Peipiaosteidae, extending back to the Upper Jurassic, and Chondrosteidae, dating from the Lower Jurassic, and extant representatives in two families: Acipenseridae and Polyodontidae (see Findeis 1997, Nelson 2006). Both extant families have fossil records with Mesozoic dating. Most primitive and the oldest paddlefishes (Polyodontidae) are known from the Lower Cretaceous of China (Protopsephurus) and North America (Paleopsephurus) (Grande and Bemis 1991); the only two living freshwater species represent two distinct phylogenetic lineages and genera (Hilton 2004): Polyodon spathula (Walbaum, 1792) in United States and Psephurus gladius (Martens, 1862) in China. Both the oldest sturgeon (Acipenseridae) species dated back to the Late Cretaceous in Montana are treated as taxa with an uncertain position, namely plesion Protoscaphirhynchus Wilimovsky, 1956, insertae sedis, and plesion Priscosturion Grande et Hilton, 2009, sedis mutabilis (see Hilton et al. 2011). The phylogenetic relations and taxonomic states of recent 25 sturgeon species also are the subject of a long-term discussion. Usually, living Acipenserid fish are subdivided into two subfamilies. Some authors (Findeis 1997, Nelson 2006) ACTA ICHTHYOLOGICA ET PISCATORIA (2014) 44 (2): 111–116 DOI: 10.3750/AIP2014.44.2.04