On the Composition and Origin of the Genera Apscheronia and Parapscheronia (Bivalvia, Cardiidae, Lymnocardiinae): New Finds in the Taman Peninsula

Apscheronia and Parapscheronia are endemic brackish-water genera of the subfamily Lymnocardiinae from the Early Pleistocene Apsheronian Basin. Apscheronia includes three species, while Parapscheronia is represented by six species. Considering new finds of the species Apscheronia propinqua in the northern part of the Taman Peninsula, in the boundary deposits of the Gelasian and Calabrian, the question of the origin of these genera of bivalves, which are index fossils for the Early Pleistocene (Calabrian) of the Caspian region, has once again arisen. The article considers the systematic composition of the genera Apscheronia and Parapscheronia and hypotheses of their origin, in connection with the history of the Apsheronian Basin. For species of the genus Parapscheronia, the most plausible version, from our point of view, is their origin through neoteny, and for species of the genus Apscheronia, through gradual smoothing and subsequent loss of ribs.