Revealing elasmobranch diversity across the Cretaceous-Paleogene boundary in the Central Tethys (Byala, Bulgaria)

Résumé fourni par la source

Extensive bulk-sampling of the continuous K-Pg succession at Byala (Central Tethys) provides high-resolution insights into elasmobranch responses to the end-Cretaceous mass extinction of a deep-marine environmental setting. The studied section represents a rhythmic alternation of marls and marly limestones of the Byala Formation, which shows exceptionally well-preserved Milankovitch cyclicity in combination with a deepening-upward trend. The sampled interval comprises one horizon from the uppermost Maastrichtian (Zone CC26), the boundary clay, and five horizons from the lowermost Danian (Zone NP1), which combined yielded a total of 535 elasmobranch teeth. The Maastrichtian assemblage is moderately diverse but strongly dominated by squaliform sharks, including Centrophoridae, Somniosidae, and Etmopteridae. Although most teeth are poorly preserved, limiting accurate estimates of original diversity, several genera typical of deep-marine Maastrichtian environments (e.g., Deania , Centrodeania , Cretascymnus , Protoxynotus , Incognitorapax ) were recovered. The sampled Danian interval shows higher elasmobranch diversity compared to the undisturbed pre-extinction environment of the Maastrichtian and a pronounced faunal turnover is described, which is marked by the appearance of Hexanchiformes (Chlamydoselachidae, Hexanchidae), Lamniformes (Carchariidae, Mitsukurinidae), and Carcharhiniformes (Triakidae). The Danian assemblages include teeth of Squalidae ( Squalus ) and Dalatiidae ( Angoumeius ), with the latter extending its fossil record into the earliest Paleocene and now spanning from the Danian to the Middle Miocene. Notably, Cretascymnus is reported for the first time in the Danian, indicating that this genus survived the end-Cretaceous extinction event. Comparison with previously studied K-Pg successions from the Northern Tethyan and Boreal realms indicates that elasmobranch extinction intensity was moderate in deep-marine and high-latitude settings, while shallower environments experienced stronger ecological restructuring.

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