New Late Aptian Ammonites of the Northwestern Caucasus

The new representatives of extinct ammonite cephalopods described in the article ,although they belong to different systematic groups, also have common features: small size, rarity and a limited range of stratigraphic distribution - known in the Upper Aptian zone Acanthohoplites nolani (Pseudojauberticeras egoiani Scharik., Paradiadochoceras fragosum Sharik., P.finitimum Scharik., Hokodziceras druschitsi Scharik.). Based on morphogenetic studies, the main trends in their onto-phylogenetic development and systematic position were determined. Representatives of the genus Pseudojauberticeras Scharik. are characterized by a high degree of differentiation and symmetrical structure of the septal line, bifurcation of its main elements, the formation of a rather large, segmented internilateral lobe, the presence of broadly oval whorls with numerous thin ribs and constrictions, which generally allows us to attribute this genus to the family Gaudryceratidae Spath. Based on the morphogenetic characteristics of the main elements of the shell of Paradiadochoceras Scharik. assigned to the subfamily Diadochoceratinae Kvantaliani, family Acanthohoplitidae Stoyanow. However, if stratigraphic distribution and sculptural trends are taken into account, the genus Diadochoceras must be the ancestor of Paradiadochoceras. Accordingly, in this family we can assume the existence of the following highly specialized dead-end phylogenetic series: Colombiceras → Protacanthoplites → Diadochoceras → Paradiadochoceras. Systematic status of the monotypic genus Hokodziceras Scharik. unclear If we take into account the presence of weakly involute whorls and, accordingly, a wide umbilicus, a low degree of differentiation of the septal line, tripartite lateral and underdeveloped internilateral lobes, then this genus at the modern level of study can be conditionally attributed to the family Ancyloceratidae Meek. The stratigraphic and paleontological significance of the described organisms is determined by their role in establishing the relative age of rocks, in the reconstruction of physical and geographical conditions, in determining the paths of evolution and systematics of ammonoids.