Middle Jurassic (Upper Bathonian and Lower Callovian) jaws of Kosmoceratid ammonites of Central Russia

Elements of the jaw apparatuses of the ammonite genus Kepplerites (Ammonoidea: Stephanoceratoidea, Kosmoceratidae, Keppleritinae) are described from two Upper Bathonian and one Lower Callovian localities of the Russian Platform. The lower jaws (aptychi), based on their size and shape can be assigned to two groups and certainly belonged to the co-occurring macroconchs K. (Kepplerites) and theirs microconchs K. (Toricellites). It is established that the presence or absence of tuberculate ornamentation on the surface calcite layer in the studied kosmoceratid aptychi (and accordingly the assignment of the aptychi of kosmoceratids to Granulaptychus-type or Praestriaptychus-type) is a result of burial and fossilization in different settings. Most likely all Kosmoceratidae had lower jaws of the Granulaptychus-type, apparently like the related subfamily Garantianinae (family Stephanoceratidae). For the first time, upper jaws of cephalopods supposedly also belonging to the ammonites of genus Kepplerites are described from the Bathonian Stage.