Taphonomical and palaeoecological investigation of the Late Cretaceous (Maastrichtian) Tuştea vertebrate assemblage (Romania; Haţeg Basin) - insights into a unique dinosaur nesting locality

Abstract

The Tuştea vertebrate locality, at Oltoane Hill (northwestern part of the Hațeg Basin, Romania), has provided a rich and diverse assemblage of Late Cretaceous (Maastrichtian) continental vertebrates. More than 800 vertebrate fossils were recovered from this locality; the isolated and associated remains represent 21 different taxa including amphibians, turtles, lizards, snakes, crocodyliforms, pterosaurs, dinosaurs and mammals. The local assemblage is overwhelmingly dominated by dinosaurs, with the rhabdodontid Zalmoxes as the most abundant taxon. The bonebeds that yielded this fossil material occur in a stacked series of mudstone/calcrete units belonging to the middle member of the Densuş-Ciula Formation. The taphonomical investigations suggest that the Tuştea assemblage is made up of attritionally accumulated politaxic remains and that it is a parautochthonous assemblage with no evidence for significant bone transport or reworking.According to the synthesis of all available field data two outstanding fossiliferous levels can be identified within the Tuştea locality, where Megaloolithus eggs and hadrosauroid hatchling material are preserved together, recognized here as two superposed nesting grounds. Such co-occurrence was considered controversial, since there is a long-standing and quasi-general consensus that eggs of the Megaloolithus oogenus were laid by titanosaurian sauropods. We present several alternative scenarios to account for the co-occurrence of Telmatosaurus hatchling remains and megaloolithid eggs in the nesting horizons and explore these alternative hypotheses by weighing the arguments supporting or contradicting them. The burden of evidence derived from our sedimentological, taphonomical and palaeoecological investigations at Tuştea is still in favour of the autochthony of the hatchlings, preserved within their own nesting grounds, whereas there is no such support for a titanosaurian origin of the Tuștea megaloolithid eggs.