Otolith morphometry of Ambassidae (Teleostei: Perciformes) reveals species diversity and faunal exchange in the late Burdigalian of the North Alpine Foreland Basin and the Central Paratethys

Fossil otoliths are a well-established tool for resolving species-level diversity in teleost fishes. However, species identification of fossil otoliths commonly relies on qualitative characters, which can introduce uncertainty regarding true species diversity, particularly when reconstructing ancient connectivity between geographically separated basins. Here we address this issue using otoliths of Ambassidae (Teleostei, Perciformes) from upper Burdigalian (Lower Miocene) brackish deposits of the North Alpine Foreland Basin (51 otoliths) and the Central Paratethys (Western Carpathian Foredeep, 8 otoliths), allowing the integration of quantitatively supported species-level diversity data with reconstructions of Early Miocene palaeoenvironmental conditions, palaeobiogeography and palaeoclimate. Based on a new quantitative approach encompassing 12 otolith variables and univariate and multivariate statistical analyses, we identify three ambassid species, including Parambassis? pipperrae n. sp. Their co-occurrence indicates ecologically structured assemblages, suggesting warm, shallow, euryhaline environments during the late Burdigalian. One species, †Dapalis formosus, is shared between the North Alpine Foreland Basin and the Western Carpathian Foredeep, providing evidence for faunal exchange between these regions. We hypothesize that monsoon-like climatic conditions associated with intensified precipitation, as suggested by previous studies, promoted episodic storm and flooding events that temporarily created dispersal pathways for euryhaline fishes, despite of the presence of topographic barriers such as the Amstetten Swell and the Landshut-Neuöttingen High. Overall, our results demonstrate that quantitative otolith morphometry significantly improves fossil ambassid taxonomy and provides a robust framework for reconstructing Early Miocene euryhaline palaeoenvironments and faunal connectivity.