Annotation of the results obtained in 2023
During the 2023 reporting period, historical literature on the Paleogene of the Volga Region from scientific libraries and geological collections was collected, digitized and analysed. Material on chondrichthyan fishes was studied using light microscopes, and using electron microscope and computer X-ray tomography. Field work was carried out in the Volga River Right Bank, Volga-Don interfluve and Don River Right Bank within the Saratov, Volgograd Regions and southern part of the Penza Region. We studied 99 geological points, including 28 previously known sections with chondrichthyan remains and 71 new geological points, and found 14 new chondrichthyan localities. Bulk sampling was carried out at 24 localities (including 17 previously known localities being sampled in a second time). In total we got 38 bulk samples with a more than 4 cubic meters of primary processed sediments being collected and secondarily processed in part. Chondrichthyan fish remains (sharks, rays and chimaeroids) have been collected from the following formations of the Volga River region: Berezovaya strata, "Dobrinka", Baltay, Petrovsk, Tsimlya, Balyklei, Solonskaya, Mechetka, Tsaritsin, Proleyka, and Kamyshin Formations, in the sandy Syzran-Saratov strata, in the sandy-siltstone strata of the Vershaut Mamber of the Baltay Formation, as well as from the Buzinovka Formation on the Don River Right Bank. A nomenclatural revision of elasmobranch taxa (three species and one subspecies) previously described from the Palaeogene of the region (L.S. Glikman, V.I. Zhelezko) was carried out: two species were recognized as valid, one species and one subspecies were reduced to synonymy with other species described earlier. The total diversity of chondrichthyan fishes from the Paleogene of the Volga River Basin was clarified, and includes 11 orders, 33 families, 80 genera (61 genera of sharks, 12 of rays and 7 of chimaeroids) and more than 130 species. The diversity of lamniform sharks was clarified, which includes 22 genera and 45 species; this order is the most biostratigraphically important. The dynamics of elasmobranch diversity in the late Maastrichtian and in Danian was analysed using layer-by-layer samples from the Danian Berezovaya Strata. A decrease in taxonomic diversity at the Cretaceous-Paleogene boundary, poor complexes of the lowest part of the Berezovaya Strata (0.3 m) with abundance of reworked Cretaceous forms, a rapid increase in diversity at 2 m above the Cretaceous-Paleogene boundary and its growth to a maximum at 3-5 m above this boundary, then another decline. These dynamics probably reflect the first (Danian) regional sedimentary cycle, with increases in diversity being correlated with transgressive conditions and decreases with regressive conditions. These trends are also noted in the ratio of two orders - the Squaliformes/Lamniformes quantitative ratio is increasing in the middle part of the Berezovaya Strata, while it is decreasing in the upper part. The decrease in the number of sharks of the Synechodontiformes and Rajiform rays in the Berezovaya time probably reflects the changes in the structure of the complexes in the end of the Cretaceous and in the early Palaeocene. A new chondrichthyan assemblage from the basal deposits of the Baltai Formation (Khvatovka Subformation) was established in the Eocene deposits of the Saratov part of the Volga River Right Bank. This assemblage is characterized by the dominance of angel sharks (Squatina) and numerous eagle rays (Myliobatis) and is a shallow-water analogue of the E7 level complexes, thus showing a pronounced facies differentiation of the same-age elasmobranch complexes. Based on the collected data we analysed the dynamics of the regional diversity of elasmobranch and chimaeroid fish complexes, palaeobiogeographical relationships within the Northern hemisphere by ages and epochs, biostratigraphic analyses of the complexes, and proposed changes and additions to the regional and local stratigraphic schemes of Paleogene deporits. A new genus and species of kitefin sharks from the Danian of the Lower Volga region were described. Three oral talks at two All-Russian scientific Meetings and one oral talk at a Youth scientific Meeting were presented. Two papers were published (WoS/Scopus, Q1) and two papers were submitted for publication (WoS/Scopus). Operational information on the project events was published on the website of the Elasmodus Research Group: http://www.elasmodus.com/ru/novosti

 

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Annotation of the results obtained in 2022
During the project, fieldworks were carried out in the Saratov-Volgograd part of the Volga Right-bank region: about 150 field sites were visited and studied, including 15 previously known localities with chondrichthyan fish remains, and 27 new localities were found. Twenty-two localities were sampled and 38 bulk samples were collected, which are mostly already processed. Chondrichthyan fish remains (sharks, rays, chimaeroids) were found in deposits of the Berezovaya strata, Saratov, Kamyshin, Proleika, Tsaritsin, Meketka, Kalinino, Solon (Kuma), "Dobrinka", Baltai, Petrov, Balykleika, Tsimlya formations, and also from Paleocene "sandy strata" on the Don slope of the Volgo-Don interfluves. For the first time, material on elasmobranchs from Upper Eocene-Oligocene carbonate complexes (Balykleika and Tsimlya formations) was collected. On the basis of the material obtained, 15 levels (time slices) with chondrichthyan fishes were identified in the Paleogene of the Volga region: 5 in the Paleocene (E1-E5), 5 in the Lower Eocene (E6-E10), 3 in the Middle Eocene (E11-E13), one in the Upper Eocene (E14), one in the Oligocene (E15), plus two additional levels (E12b in the Lutetian, E13b in the Bartonian) in the adjacent region (north-east of Rostov Region). The total diversity of Paleogene chondrichthyan fishes from the Volga Region was calculated as 11 orders and 73 genera (58 genera of sharks, 8 genera of rays and 7 genera of chimaeroid fishes). The diversity of lamniform sharks includes 21 genera and 35 species, this order is the most biostratigraphically important. New data will allow to propose 8-9 additional biostratigraphic subdivisions in Paleogene scheme of the region in the rank of "beds with fauna". Analysis of chondrichthyan fish complexes from the Danian Berezovaya strata (Danian complex E1 and Maastrichtian complex E0 from the basal horizon of the strata) shows no pronounced effect of mass extinction on the Boreal cartilaginous fish complex: the extinction of 5 genera of elasmobranchs was compensated by the appearance of 8 new genera, chimaeras had a renewed species composition; the Danian chondrichthyan complex is more diverse (E1 - 33 genera, E0 - 19 genera) but includes 30% of southern (Tethys) taxa, apparently reflecting the influence of southern water masses and/or general warming in the early Danian age. The small sand shark species Carcharias gracilis dominates both complexes and successfully crosses the K/T boundary. Analysis of the 4 Early Eocene complexes (E7, E8, E10 and E11) from the Kalinino, Baltai and Petrov formations of the Saratov part of the Volga Right-Bank region showed changes in diversity (maximum in E7: 21 shark species, 2 batoid species and 1 chimaeroid species), successive change of dominants (Sylvestrilamia - Xiphodolamia - Striatolamia) and general change in complexes as a reflection of paleobasin (depth increase) changes. For the remaining formations the material is in processing. One poster was presented at the All-Russian scientific meeting and two oral presentations were made at the youth scientific meeting. One paper was published (RSCI) and two manuscripts were submitted for publication (WoS/Scopus). Operational information on the project events was published on the website of the 'Elasmodus' research group: http://www.elasmodus.com/ru/novosti

 

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