Ammonites and infrazonal subdivision of the Dorsoplanites panderi zone (Volgian Stage, Upper Jurassic) of the European part of Russia

Eight biohorizons, four of which were previously distinguished in Central Poland and four new (contradictionis, pommerania, kuteki, and pilicensis), were identified in the Dorsoplanites panderi zone of the Upper Jurassic Middle Volgian Substage of the European part of Russia on the basis of the succession of ammonites of the Zaraiskites genus. The peculiarities of variations of the ammonite complexes in space and time testify to the stepwise warming during the Panderi Chron and the occurrence of the significant latitudinal temperature gradient in the Middle Russian Sea. New species Zaraiskites kuteki is described.