Palaeopathologies in Upper Jurassic turtle shells – their origin and significance for the evolution of biotic interactions

The study of bioerosion traces on the carapaces of Upper Jurassic turtles from Krzyżanowice, located in the northeastern margin of the Holy Cross Mountains in Poland, sheds light on the complex biotic interactions and palaeoecological dynamics of Mesozoic ecosystems. The research focuses on enigmatic pathologies observed on the turtle shells, combining histological, morphological, and palaeoenvironmental analyses to explore their origins and significance. Evidence of bone remodelling within the pathologies strongly supports their formation during the life of the turtles, suggesting interactions such as parasitism, symbiosis, and failed predation attempts. The variability in pathologies morphology—ranging from shallow, smooth-bottomed depressions to deep, irregular cavities—points to a diversity of bioeroders, including echinoids, microbial colonizers, and scavenging invertebrates. While remodelling suggests live damage in many cases, post-mortem bioerosion may have also contributed to the traces, particularly in low-energy, shallow marine environments. The findings highlight turtles as ecological hubs, playing vital roles as both substrates and participants in complex biotic interactions. Over geological time, a shift from symbiotic and parasitic traces to predation-related marks reflects changing ecological pressures and predator specialization. This study underscores the importance of turtles as indicators of palaeoenvironmental conditions and as resilient components of their ecosystems, capable of surviving repeated interactions with other organisms. By integrating modern analogs and fossil evidence, this research provides new perspectives on the evolutionary and ecological significance of bioerosion in the fossil record.