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A new species of the genus Belebey (Bolosauridae), Be. shumovi sp. nov., is described from the Upper Kazanian Substage (Guadalupian) of European Russia based on elements of the upper jaw, a maxilla and two premaxillae. This is the largest known bolosaurid, the skull length of which could be estimated to be around 160 mm. In addition to its overall size, Be. shumovi differs from other species of the genus in the shape of the maxilla, maxillary teeth, and their distribution along the tooth row. The holotype of Be. shumovi (maxilla) exhibits marginal dentition at the earliest stage of the tooth replacement process. Computed tomography (CT) scan data indicate the presence of almost completely formed replacement teeth along the entire tooth row, confirming the hypothesis of a single-wave cycle of tooth replacement in bolosaurids. Based on the material studied, the tertiary dentine formation was discovered for the first time among fossil reptiles. The tertiary dentine is one of the most evident adaptations of bolosaurids to high-fibre herbivory and demonstrates uniformity of the protection mechanism of the pulp in tetrapod history throughout most of the Phanerozoic. [ABSTRACT FROM AUTHOR]