Mitta Vasily, Mironenko Aleksandr (2021) Middle Jurassic (Upper Bathonian and Lower Callovian) jaws of Kosmoceratid ammonites of Central Russia PalZ, 95, 61–69


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 diferent settings. Most likely all Kosmoceratidae had lower jaws of the Granulaptychus-type, apparently like the related subfamily Garantianinae (family Stephanoceratidae). For the frst time, upper jaws of cephalopods supposedly also belonging to the ammonites of genus Kepplerites are described from the Bathonian Stage.


Various types (or formal genera) of aptychi are characteristic of different ammonite lineages. However, aptychi are not known for all genera of ammonites and in some cases, although aptychi are known, attributing them to one or another formal genus is difficult due to incomplete preservation. In this article, we for the first time show that Lower Callovian Kosmoceratidae (subfamily Keppleritinae) have Granulaptychi, but not Praestriaptychi, as i was previously assumed. The problem is that small calcitic tubercles on the surface of aptychi, which are a distinctive feature of Granulaptychi, are usually very poorly preserved. We also described for the first time the upper jaws of Keppleretinae, which have a very unusual structure.


Ammonites, Cephalopod jaws, Aptychi, Granulaptychi, Kepplerites, Bathonian, Callovian, Central Russia