MIDDLE AND LATE CALLOVIAN APTYCHI (AMMONOIDEA) OF THE RUSSIAN PLATE

Abstract

All known records of Middle and Late Callovian aptychi from the Russian Plate are revised. Aptychi first figured in the 19th century by S.N. Nikitin and I.I. Lahusen are refigured and described. The re-exam- ination of the holotype Praestriaptychus kostromensis Trauth, 1930, originally identified as "Aptychus des Cos- moceras galilaei Nikitin," showed that it is an imprint of a bivalve shell (Astartidae). Aptychi figured by Lahusen (1883) and specimens from my collection are assigned to the genera Praestriaptychus and Kos- mogranulaptychus gen. nov. Relationships between the so-called smooth aptychi of the Middle Jurassic and ammonite taxa are discussed. A phylogenetic scheme for the genera Praestriaptychus, Laevaptychus, Kos- mogranulaptychus, and Granulaptychus, based on the associated occurrences of aptychi and ammonites, in the context of ammonite phylogeny is proposed. A new genus, Kosmogranulaptychus (with the type species K. call- oviensis (Trauth)), and two new species, Praestriaptychus ryasanensis and Kosmogranulaptychus lahuseni, are described.