Shifts in composition of northern Tethyan elasmobranch assemblages during the last millennia of the Cretaceous

Extensive bulk sampling of seven horizons of a continuous succession deposited in an outer neritic environment of the latest Maastrichtian yielded more than three thousand ichthyoliths, including 1347 elasmobranch teeth. The sampled succession represents a characteristic deep-water fauna dominated by small squaliform sharks with an increase of species richness towards the end of the Cretaceous. The multidisciplinary approach of precise sampling in combination with a well-founded biostratigraphic classification of seven assemblages provides rare and direct evidence of diversity fluctuations within the latest Maastrichtian, immediately before the bolide impact triggered the severe mass extinction event at the K/Pg boundary. Although squaliform sharks dominate the fauna, a conspicuous heterogeneity of species abundance between the assemblages is observed and a noteworthy correlation between squa-liform species richness and the abundance of Parasquatina zitteli (Orectolobiformes) might indicate clade competition for ecological niches. Among 15 elasmobranch species, this study describes one new genus (Fredipristis gen. nov.) and four new squaliform species (F. eximia gen. et sp. nov., Eoetmopterus davidi sp. nov., Proetmopterus lukasi sp. nov., and Cretascymnus beauryi sp. nov.), which highlights the importance and potential of bulk sampling for reconstructing elasmobranch diversity of deep-marine realms through time.(c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

Extensive bulk sampling of a continuous succession in an outer neritic environment of the latest Maastrichtian reveals a deep-water fauna dominated by small squaliform sharks. The sampling provides rare evidence of diversity fluctuations before the mass extinction event, and a correlation suggests clade competition for ecological niches. The study also introduces new genus and species of squaliform sharks, highlighting the importance of bulk sampling in reconstructing elasmobranch diversity.