Petre?ti-Arini - an important but ephemeral Late Cretaceous continental vertebrate site in the southwestern Transylvanian Basin, Romania

Vremir, Mátyás, Bălc, Ramona, Csiki-Sava, Zoltan, Brusatte, Stephen, Dyke, Gareth, Naish, Darren and Norell, Mark (2014) Petre?ti-Arini - an important but ephemeral Late Cretaceous continental vertebrate site in the southwestern Transylvanian Basin, Romania. Cretaceous Research, 49, 13-38. (doi:10.1016/j.cretres.2014.02.002).

Abstract

The Transylvanian region of Romania preserves some of the most unusual and iconic dinosaurs in the global fossil record, including dwarfed herbivores and aberrant carnivores that lived during the very latest Cretaceous (Maastrichtian) in an ancient island ecosystem (the Ha?eg Island). A series of artificial outcrops recently exposed during a hydroelectric project, the Petre?ti-Arini section near Sebe? in the Transylvanian Basin, records a 400+ meter sequence documenting the transition from fully marine to terrestrial environments during the Campanian–Maastrichtian. Calcareous nannofossil biostratigraphy indicates that the lower marine beds in this section, part of the uppermost Boze? Formation, can be assigned to the CC22 biozone, corresponding to the lower–mid upper Campanian. These beds smoothly transition, via a brackish-water unit, into the fully continental Maastrichtian Sebe? Formation. Dinosaur and pterosaur fossils from the uppermost Boze? Formation can be assigned a late Campanian age making them the oldest well-dated terrestrial fossils from the Ha?eg Island, and indicating that the classic Ha?eg dinosaur fauna was becoming established by this time, coincident with the first emergence of widespread land areas. Vertebrate fossils occur throughout the overlying Sebe? Formation at the site and are dominated by the small-bodied herbivorous dinosaur Zalmoxes. The dominance of Zalmoxes, and the absence of many taxa commonly seen elsewhere in Maastrichtian sites in Romania, suggests the possibility that either the Petre?ti-Arini section preserves a somewhat unusual near-shore environment, or the earliest Ha?eg Island dinosaur communities were structured differently from the more diverse communities later in the Maastrichtian. Alternatively, due to the limited sample size available from the studied succession, it is also conceivable that sampling biases give an incomplete portrayal of the Petre?ti-Arini local fauna. Support for any one of these alternative hypotheses requires further data from Petre?ti-Arini as well as from the larger Transylvania area.

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