Not only boring issues: bioerosion on bones from the Upper Cretaceous of the Haţeg Basin (Romania) and the implications for carcass decomposition on Haţeg Island

Bioerosion of fossil bones provides insights into trophic relationships as well as carcass decomposition processes in past ecosystems. Despite this potential, however, exhaustive documentation of traces of bioerosion for specific deep-time vertebrate assemblages is rarely done. Such occurrences are present in the uppermost Cretaceous continental deposits from Haţeg Basin, famous for their rich, island-dwelling vertebrate faunas, that previously yielded several examples of bioerosion on bones although only few instances have been described in detail and those are largely limited to a single lithostratigraphic unit. For this study, an extensive survey of these vertebrate assemblages was conducted, yielding several new examples from three further lithostratigraphic units. The newly identified traces occur on turtle and dinosaur remains, and include six morphotypes attributable to termites, dermestid beetles, and multituberculate mammals. These results demonstrate that bioerosional traces are more widely distributed in the uppermost Cretaceous of Haţeg Basin, both spatially and temporally, than previously recognized and occur on bones from various paleoenvironmental settings. Notably, all traces indicate a prolonged exposure before final burial, which appears to have been a consistent feature of the sampled paleoenvironments. Nonetheless, regional differences are evident, and bioerosional traces are less common in poorly drained paleoenvironments than in better-drained ones. Finally, the mode of carcass decomposition appears to have been similar across all sampled localities, irrespective of geological age or depositional environment, and involved a consistent set of saprophagous animals, suggesting a stable composition of the saprophagous communities, aligning well with the presumed faunal stability of Haţeg Island.