A number of localities in Transylvania (Romania) have yielded vertebrate microfossil remains. Two localities have been stratigraphically and biochronologically dated to the late Eocene: i.e., Treznea and Bociu. The remaining three localities are dated to the early Oligocene: Mera, Cetățuie, and Suceag. The study of cricetid rodents corroborates the presence of this family in Eastern Europe during the late Eocene, as evidenced by the species Witenia sp., Bustrania cf. B. dissimile , and Eocricetodon cf. Eo. meridionalis. The cricetids identified in the sites of the early Oligocene age show a complete turnover and a notable increase in species richness following the Eocene/Oligocene boundary, with: Eucricetodon aff. Eu. huerzeleri, Tenuicricetodon arcemis gen. et sp. nov., Pseudocricetodon cf. Ps. montalbanensis, Paracricetodon cf. Pa. walgeri, Paracricetodon kavakderensis, Paracricetodon aff. Pa. stojonovici, and Paracricetodon wentgesi. In the context of the wider biogeographic history of Europe, these new discoveries indicate that Cricetidae arrived in Europe during at least two successive migrations from Asia in the late Eocene and earliest Oligocene. These migrations may have occurred via two different migration pathways through the north and south of Europe. In a second phase, Cricetidae arriving by the northern passway spread throughout Europe, whereas Cricetidae that arrived by the southern passway remained restricted to the central and southeastern Europe. The observations made on the Cricetidae allow for the proposal of a new, more general, scenario for the Eocene–Oligocene transition on a European scale, which is more complex than the “Grande Coupure” sensu stricto as initially proposed by Stehlin in 1909.
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Acting as a buffer between the Danube and the Black Sea, the Danube Delta plays an important role in regulating the hydro-biochemical flows of this land-sea continuum. Despite its importance, very few studies have focused on the impact of the Danube Delta on the different fluxes between the Danube and the Black Sea. One of the first step to characterize this land-sea continuum is to describe the bathymetry of the Delta. However, there is no complete, easily accessible bathymetric data on all three branches of the Delta to support hydrodynamic, biogeochemical or ecological studies. In this study, we aim to fill this gap by combining 4 different datasets, three in the river and one for the riverbanks, each varying in density and spatial distribution, to create a high-resolution bathymetry dataset. The bathymetric data was interpolated on a hybrid curvilinear-unstructured mesh with an anisotropic Inverse Distance Weighting (IDW) interpolation method. The resulting product offers resolutions ranging from 2 m in a connection zone to 100 m in one of the straight unidirectional channel. Cross validation of the dataset underlined the importance of the data source spatial pattern, with average Root Mean Square Error (RRMSE) of 0.55 %, 6.3 % and 27.6%, for river segments covered by the densest to the coarsest dataset. These error rates are comparable to those observed in bathymetry interpolation in rivers with similar source datasets. The bathymetry presented in this study is the first unique, high-resolution, comprehensive and easily accessible bathymetric model covering all three branches of the Danube Delta. The dataset is available at https://doi.org/10.5281/zenodo.14055741.
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