The effect of the Tethyan seaway closure on the Oligo-Miocene marine benthic diversity and distribution around Eurasia

The Cenozoic evolution of the Tethyan seaway significantly shaped marine and terrestrial biota around Eurasia. The Tethys connected the Atlantic and the Pacific during the early Cenozoic, allowing marine faunal exchange. However, during the Early Miocene, the “ Gomphotherium Landbridge” developed, restricting the marine connection between the proto-Mediterranean in the west and the provinces in the eastern Tethys. In contrast to the well-documented phenomena of terrestrial mammalian exchange through the land connection brought by the closure, little is known about its impact on marine fauna. To assess the overall effect of this separation on the distribution and diversity of marine organisms, we studied the Oligo-Miocene fossil record of marine benthos including Cnidaria, Echinodermata, Foraminifera, and Mollusca. We compiled 15894 reported occurrences from the Early Oligocene to Late Miocene comprising 1477genera, 404 families, and 85 orders from four faunal provinces and evaluated their paleobiogeographic patterns. Our study demonstrates that the proportion of genera shared between the eastern and western provinces decreased after the Early Miocene. The majority of the non-shared family developed during or after the Early Miocene. A high faunal diversity during the Early Miocene and increasing endemicity among the eastern province are consistent with the development of a shallow seaway that supported speciation and reduced biotic exchange. The considerable variation in the magnitude and timing of the response across taxonomic groups reflect the combined effects of preservation bias, and the differential response of fauna. Our study supports an Early Miocene initiation of the Tethyan seaway closure, followed by intermittent connectivity before the complete closure that shaped the overall diversity and distribution of the Eurasian marine benthos. Supplementary material at https://doi.org/10.6084/m9.figshare.c.7266388