Decapod crustacean from the Qom Formation (Lower Miocene) of the Isfahan area, Central Iran

The discovery of a new specimen of Portunus withersi (Glaessner 1933) from the Lower Miocene Qom Formation in the Vartun section, north of Isfahan (Central Iran), contributes to our knowledge of this portunid species, to which most fossil portunids found in the Miocene of Iran have been attributed. New images of the holotype are also presented herein. The Miocene decapod fauna of Iran, exhibiting a clear Indo-Pacific affinity, reflects an emerging loss of faunal homogeneity between the decapod communities on either side of the Tethys Realm. This differentiation is related to the progressive closure of the Tethys Seaway, which interrupted the connection between the proto-Mediterranean and Paratethys seas and the Indian Ocean. This stands in contrast to the relative faunal homogeneity observed during the Paleogene, as evidenced by the presence—on both sides of the Tethys Realm—of genera such as Zanthopsis M’Coy 1849, Palaeocarpilius A. Milne-Edwards 1862, or Lophoranina Fabiani 1910, among others, and even species such as Retrocypoda almelai Vía Boada 1959.