Based on the study of a representative collection of Cylindroteuthididae rostra from the Ryazanian–lower Hauterivian deposits of the Anabar region (Nordvik Peninsula, Anabar River, eastern shore of the Gulf of Anabar), the ideas about the taxonomic composition and stratigraphic distribution of belemnites in the Lower Cretaceous of northern East Siberia have been significantly refined. Analysis of taxonomic and paleoecological rearrangements with an assessment of the impact of environmental factors has shown a noticeable influence of changes in the depth of the paleobasin, both on the dynamics of the taxonomic diversity of belemnites and on the ecological structure of their communities. The influence of the climatic factor in the study of biodiversity curves constructed for separate sections is not obvious for all time intervals. At the end of the Berriasian–beginning of the Valanginian, intensive migrations-influences of nektobenthic forms of belemnites of low-boreal European origin are recorded, which leads to a significant change in the taxonomic and ecological structure of the Anabar belemnic communities. In this regard, the Berriasian and Valanginian stages of their development are clearly distinguished, but at the same time, a transitional stage is recognized, which falls on the second half of the late Berriasian.
V.D. Efremenko (Wed,) studied this question.