The Discovery of Diadectomorph Tetrapods in the Lower Permian of Eastern Europe

Abstract

The systematic position of the bolosaurid Stephanospondylus (Bolosaurus) traati (Tatarinov, 1974) is reassigned to the family Diadectidae (Diadectomorpha). This taxon is the first diadectomorph described from the Eastern Europe. Simple shape of the cheek teeth, as well as the pattern of the tooth differentiation along the maxilla indicate the basal position of S. traati within Diadectomorpha and its primitiveness in comparison with the type species to the genus Stephanospondylus, S. pugnax. The genus Ambedus Kissel et Reisz, 2004 is excluded from the order Diadectomorpha basing on the discrepancy of its marginal dentition to that of the other species of the group. The similarity of the dental system of Ambedus and diadectids is regarded as convergent rather than being due to its phylogenetic position, thus, the systematic position of this genus remains uncertain. The early stages of specialization of the dental system in the evolution of the family Diadectidae are discussed.