Maastrichtian dinosaur eggshells from Transylvanian and Hateg sedimentary basins (Romania) unveil the northernmost occurrence of fusioolithidae

Resumen

The presence of isolated Maastrichtian eggshells at the Oarda de Jos and Nălaț-Vad sites, in thesedimentary basins of Transylania and Hațeg, is here reported. In both basins, the sedimentaryinfill sequences refer to fluvial environments, with volcanic inputs. These rocks are famous due totheir vertebrate fossils: fish, amphibians, lacertilians, dinosaurs, pterosaurs, birds, and mammals.Eggshells from both localities have dinosaur-spherulitic basic type, tubospherulitic morphotypewith partially fused spheroliths, tubocanaliculate pore system and compactituberculatedornamentation with some nodes connected by ridges. This trait combination is compatible withthe widespread oospecies Fusioolithus baghensis, and thus these Romanian specimens representthe northernmost known occurrence of Fusioolithidae. Though differences in histostructuralfeatures between the specimens from those sites, particularly related to eggshell thickness andnode shape, have been observed, all of them more closely resemble other European specimensrather than those from Gondwana. Eggshells from Nălaț-Vad are slightly thicker than the typicalFusioolithus baghensis eggshells, being similar to those from Coll de Nargó and Orcau-1 sites(Lleida, Spain) but with predominantly dome- or wave-shaped nodes. The Oarda de Jos specimensare more akin to the Fusioolithus baghensis specimens from Poyos fossil site (Guadalajara,Spain), being remarkably thin with bell- or wave-shaped nodes. Interestingly, eggshells from bothRomanian sites have spheroliths with a higher height/width ratio than most worldwide sites, beingonly comparable to those from Poyos. Fusioolithus baghensis eggs with in ovo titanosauriansauropod embryos have been reported from Gondwana. The titanosaur diversity in the Europeanrecord is still poorly understood, but they were subject to vicariant processes between islandsand insularity at the end of the Cretaceous. The unclear phylogenetic connections betweentitanosaurs in Romania and Spain underscore the significance of these findings in shedding lighton the evolutionary history and distribution patterns of these dinosaurs during the European UpperCretaceous