L.A. Nevesskaya’s research while affiliated with Russian Academy of Sciences and other places

The Handbook of Phanerozoic Bivalve Mollusks contains diagnoses of three superorders, 17 orders, 102 superfamilies, 273 families, and more than 1500 genera of bivalve mollusks known from the extratropical zone of Eurasia, and sometimes beyond this territory, when they are important for understanding the history of the development of the group. For almost all genera and subgenera, images are given - photographs or drawings of type species. The introductory part presents data on the anatomy and morphology of bivalves, their ontogenesis, shell formation and its microstructure. The ecology of the group, the composition of marine benthic communities, which included bivalves, are described. The main ethological-trophic groups are identified, their morphological characteristics are given, and the change in the taxonomic composition of individual groups during the Phanerozoic is traced. The main directions of changes in the shell morphology are traced. The principles of systematics and the system of this class are outlined. Based on these data, changes in the systematic composition and dynamics of the taxonomic diversity of bivalves were revealed during geological time.

Evolution of the bivalve and gastropod mollusks is considered under conditions of the biochore isolation, ecosystem impoverishment, and competition weakened in the Cenozoic marine half-closed and nearly closed brackish basins during the last 30 million years (Oligocene to Pliocene). In these environments, the mollusks have first undergone drastic impoverishment of the taxonomic composition at expense of stenobionts, followed by a rapid diversification of few survived eurybiotic taxa accompanied by formation of numerous endemic species, genera, and occasionally families. Diversification rates used to rise drastically with the stability disturbance in the benthic ecosystems. Evolutionary transformations of mollusks under such circumstances surpassed frequently ranges of the ecological space of the respective taxa in their original marine basins (extralimital specialization). The morphological changes resulted often display features of fetalization, that is, retarded development with final stages lost. Constraints of morphogenetic potentials may become apparent as morphological similarity (homeomorphism) of closely or, occasionally, distantly related groups under both similar and dissimilar environments. Homeomorphism often poses problems in classification of the affected taxa and sometimes makes necessary a compromise between the pure morphological and pure genealogical approaches.

The palaeogeographic evolution of the Paratethyan and Mediterranean realms are reconstructed with three maps ranging from the Late Miocene to the Middle–Late Pliocene. The maps are based on the facial analysis of selected deposits, clastic input, slope-slide process analyses as well as biogeographic data of the planktic, benthic and terrestrial biota. Characteristic fossil assemblages are used for palaeobathymetric and palaeohydrologic interpretations, restoration of palaeogeographic connections. The palaeogeographic reconstructions are palinspastically restored (after [Dercourt, J., Ricou, L.-E., Vrielynck, B. (Eds.), 1993. Atlas Tethys Palaeoenvironmental Maps. Gauthier-Villars, Paris, pp. 1–307, 14 maps; The Paleogeographic Atlas of Northern Eurasia, 1997. Inst. Tectonics Lithospheric Plates. Moscow. 26 maps], with modifications). Maps have been prepared for the terminal Tortonian/early Messinian–Late Pannonian/early Maeotian, Late Messinian–Pontian (salinity crisis time) and Piacenzian/Gelasian–Akchagilian. They illustrate the Neogene palaeogeographic evolution during and after the Attic orogenesis. Though the emerging mountain system of the Alpine foldbelt increasingly separated the Paratethys from the Mediterranean, Tethys–Paratethys connections remained extant and sufficiently effective for limited communication between both basins. They governed many features of the cyclic depositional history and biogeographic evolution of the Eastern Paratethys.

The Neogene stratigraphic scale comprising 12 regional stages of the Eastern Paratethys is discussed. The stratotype, its lithology, and characteristic micro- and macrofossils are given for every regional stage with indication of their stratigraphic position and probable correlation with regional stages of the Western Paratethys and with stages of the Mediterranean scale. Paleogeographic features of the Eastern Paratethys and its links with other basins are characterized for every stage of the Neogene history. A particular attention is paid to boundaries of series and subseries. The lower Neogene boundary is arbitrarily drawn in the lower part of the Caucasian regional stage, the lower-middle Miocene boundary is drawn within the Tarkhanian regional stage, and the middle-upper Miocene boundary is placed within the uppermost middle Sarmatian regional stage. The Miocene-Pliocene boundary coincides with the top of the Pontian regional stage whereas the Neogene-Quaternary boundary is placed slightly above the upper boundary of the Akchagylian regional stage.