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Mitta V.V. (2021) On the Zonal Index-Species of the Standard Scale of the Ryazanian Stage on the Russian Platform // Paleontological Journal. Vol. 55. No. 3. Pp. 277287.

The validity and index species of the standard ammonite-based zones (from bottom to top: Rjasanensis, Spasskensis, and Tzikwinianus zones) of the Ryazanian Stage in the type region are discussed. The species Surites spasskensis (Nikitin, 1888) and S. tzikwinianus (Bogoslowsky, 1896) are re-examined and re-described. It has been established that these two phylogenetically successive species characterize two adjacent intervals of the geological section. For the first time, photographs of holotypes (by monotypy) of these species and of the lectotype of Riasanites rjasanensis (Nikitin, 1888) are published.



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