Early Cretaceous Rhynchonellids of Dagestan: System, Morphology, Stratigraphic and Paleobiogeographic Significance

A comprehensive report on Early Cretaceous Dagestan rhynchonellids is provided for the first time. It includes the rhynchonellid system based on detail morphofunctional studies, recognition of the boundary in the evolutionary development of Late Mesozoic rhynchonelloids at the Barremian-Aptian boundary, analysis of changes in shell matter structure during successive time periods of the Early Cretaceous, elucidation of stratigraphic importance of species assemblages allocated stratigraphically by layers to six sections of the Lower Cretaceous deposits described by the author, and revelation of possibilities of using this group in paleobiogeographic reconstructions. The study describes 37 species, 7 genera, and 2 families; 16 species and 2 genera are new. This paper is useful for a wide range of paleontologists, experts on the Mesozoic fauna, biostratigraphers, and geologists dealing with Mesozoic deposits. The study provides 8 plates, 58 figures, 71 references. DOI: 10.1134/S0031030112110019