Decapod Crustacea of the Central Paratethyan Ottnangian Stage (middle Burdigalian): implications for systematics and biogeography.

Decapod crustaceans from the Ottnangian (middle Burdigalian, Lower Miocene) of the Western and Central Paratethys remain poorly known. In this study, we review and re-describe mud shrimps (Jaxea kuemeli), ghost shrimps (Gourretia sp., Calliax michelottii) and brachyuran crabs of the families Leucosiidae, Polybiidae and Portunidae. A dorsal carapace of the genus Calliax is reported for the first time in the fossil record. Re-examination of the type material of Randallia strouhali (Leucosiidae) and Geryon ottnangensis (Geryonidae) resulted in a transfer of these species into Palaeomyra (Leucosiidae) and Liocarcinus (Polybiidae), respectively. Achelous vindobonensis, originally described as a chela of a portunid crab, probably belongs to a member of Polybiidae and is provisionally treated as Liocarcinus sp. Only two species, J. kuemeli and C. michelottii, are also known from the Karpatian, the succeeding Paratethyan stage. In most cases, the decapod assemblages of the Ottnangian consist of rather shallow-water taxa whereas the assemblages of the Karpatian consist of deep-water taxa from the middle and outer shelf. The Central Paratethyan assemblages show similarities in genus composition to the Proto-Mediterranean and recent Indo-Pacific regions. Gourretia sp. represents the earliest occurrence of the respective genus in the fossil record. The Oligocene-Early Miocene appearance of Palaeomyra and Liocarcinus in the circum-Mediterranean implies that sources of present-day diversity hotspots in the Indo-Pacific trace to the Western Tethys (as for other decapod genera), although coeval decapod assemblages in the Indo-Pacific remain poorly known.