Vol 53, No 6 (2019)

The Vendian–Cambrian transitional strata of the Igarka Uplift (northwestern Siberian Platform), originally erected as the Sukharikha Formation, are one of the key objects revealing evolution of marine ecosystems in the late Vendian. Herein we describe dwelling burrows Skolithos and Arenicolites from dolostones in the middle Sukharikha Formation (Nemakit-Daldynian Regional Stage). High density and local distribution of these burrows in the Sukharikha Formation demonstrate that the terminal Vendian shallow-marine sediments became occupied by vertical-burrowing benthic organisms, mirrored in the geological record as an archetypical Phanerozoic ichnoassemblage (Skolithos ichnofacies).

The morphology and shell microstructure of smooth exogyrid oysters from the Upper Maastrichtian of the Mountainous Crimea (SW Russia) are studied. Their shell microstructure consists of a simple regularly foliated, irregular crossed foliated, and transitional irregular simple prismatic/irregular complex crossed foliated structures. The latter has been only identified in oysters of the genus Rhynchostreon Bayle. Along with specific shell morphology, it allows to attribute the studied oysters to the species Rhynchostreon aralensis (Arkhangelsky, 1912). The occurrence of the genus Rhynchostreon in the Upper Maastrichtian of the Mountainous Crimea allows to clarify its stratigraphic distribution.

The short geochronological span and wide geographic distribution of the genus Hectoroceras in the Boreal Paleogeographic Superrealm make it exceptionally important for correlation of the Volgian–Ryazanian boundary beds. The Ogarkovo Section on the Unzha River (Kostroma Region), which is essential for this correlation, is described. The revised genus Hectoroceras includes the type species H. kochi Spath, H. larwoodi Casey, H. tolijense (Nikitin), and its microconch H. pseudokochi (Mesezhnikov), the latter two previously assigned to the genus Shulginites Casey, 1973 which is here considered as a junior subjective synonym of Hectoroceras. The FAD of Hectoroceras kochi is an interregional marker for Panboreal correlation, and the coincidence of this event with the invasion of ammonites of Tethyan origin into the Central Russian ecotone improves the prospects for a Boreal – Tethyan correlation of the Jurassic–Cretaceous boundary interval.

Smooth ostracods have a limited set of diagnostic features due to the lack of sculpture on the surface of the shell. The main species characteristics include the shell outline on the lateral and dorsal sides. The lack of a unified terminology has led to uninformative descriptions of Permian and Triassic smooth ostracods. The article presents a new method for measuring the parameters characterizing the ostracod shell shape. Based on these parameters and their ratios, terms are introduced to describe the species. The new method, in conjunction with statistical analysis, will help solve biological, environmental and biostratigraphic issues.

A new dipnoan genus and species Anchidipterus dariae Krupina, gen. et sp. nov. (Dipteridae) is described based on a lower jaw specimen from the Famennian (Upper Devonian) of the Bilovo locality (Russia, Tver oblast, Toropets district). This taxon is characterized by the short and broad mandibular symphysis, the rostrolateral orientation of the mesial ridge of the prearticular tooth plates and the significant divergence angle of their ridges. The platysymphyseal construction of the lower jaw in Anchidipterus in combination with relatively small and widely spaced tooth plates suggest that this fish fed on poorly armored or soft-bodied, inactive invertebrates and occupied the niche of an unspecialized omnivore in the trophic structure of the community.

New finds of fossil remains of ruminants of genera Euprox Stehlin, 1928 (Dicrocerini, Muntiacinae, Cervidae) and Protragocerus Depéret, 1887 (Boselaphini, Bovinae, Bovidae) and the faunal analysis clarify the age of the terrestrial fauna from the Fortep’yanka River composite section. We show that the fauna corresponds to the early Vallesian, mammal zone MN 9 of Europe and belongs to the first half of the Tortonian, upper Sarmatian (Khersonian regional stage) of the Eastern Paratethys.