The Early Pleistocene freshwater mollusks of the Denizli Basin (Turkey): a new long-lived lake fauna at the crossroads of Pontocaspian and Aegean-Anatolian realms

We describe here a newly discovered, diverse fossil fauna of freshwater gastropods and bivalves from the Denizli Basin in SW Turkey. The material was collected from the Kolankaya Formation, for which latest chronostratigraphic and magnetostratigraphic data indicate an Early Pleistocene age, which is much younger than previously assumed for the fossil-bearing strata of the Denizli Basin. The fauna consists of at least 27 species (25 gastropods, 2 bivalves) and includes a new genus, Harzhauseriagen. nov., and 6 new species within the Hydrobiidae: Falsipyrgula ? coronatasp. nov., Graecoanatolica ? alcicekorumsp. nov., Harzhauseria schizopleuragen. et sp. nov., Iraklimelania minutissimasp. nov., Iraklimelania submediocarinatasp. nov., and Xestopyrguloides ? sagittasp. nov. Additionally, we define lectotypes for Staja orientalis (Bukowski, 1896) and Valvata orientalis Fischer, 1866, as well as a neotype for Theodoxus percarinatus (Oppenheim, 1919). Nine of the recovered species (33.3%) are only known from the Denizli Basin. Almost half of the fauna (44.7%) is endemic to the Aegean–Anatolian region, with biogeographical affinities to the Pliocene–Early Pleistocene faunas of Rhodes, Kos, and mainland Greece, as well as the Çameli and Eşen Basin in Turkey. On the genus level, the fauna also contains several typical Pontocaspian elements. The composition points toward a typical long-lived lake environment with oligohaline conditions.