Fossil Turtle Shells Reveal 46-Million-Year-Old Marine Interactions

Researchers have uncovered detailed evidence of complex biological interactions in ancient marine ecosystems by analyzing the shells of two sea turtle fossils from the middle Eocene of Belgium. The study, published in the Fossil Record, focuses on bioerosional marks preserved on the carapaces of Eochelone brabantica and Puppigerus camperi, offering a rare glimpse into the physical stressors and ecological relationships that existed approximately 46 to 48 million years ago. By combining macroscopic examination with advanced imaging techniques, scientists were able to distinguish between damage inflicted while the animals were alive and alterations that occurred after death, providing a clearer understanding of how these prehistoric reptiles interacted with their environment and other organisms.

The specimens examined in this study are housed at the Royal Belgian Institute of Natural Sciences in Brussels and originate from the Lutetian stage of the middle Eocene. The first individual is the holotype of Eochelone brabantica, discovered in Saint-Remy-Geest in the Walloon Brabant region, while the second is a carapace of Puppigerus camperi found in Zaventem in the Flemish Brabant Province. Both fossils were recovered from the Brussels Sand Formation, a marine stratigraphic unit that has been correlated with the calcareous nannofossil NP14 biozone. This geological context places the animals in a littoral environment, where they would have been exposed to a variety of predators, parasites, and physical hazards typical of shallow marine habitats.

The analysis of the Eochelone brabantica shell revealed multiple erosive anomalies on its costal plates, two of which showed clear signs of bone remodelling. This remodelling is a critical indicator that the turtle was alive when the damage occurred, as the body’s healing response creates new bone tissue around the injury. The most prominent mark, located on the left first costal plate, is an amorphous penetrative lesion measuring approximately 4.5 centimeters in length and 2.5 centimeters in width. It features smooth margins and an asymmetric ridge-shaped bone growth on the inner surface, suggesting a significant healing process. Another distinct mark on the left second costal plate is a circular hole about 1.7 centimeters in diameter, which penetrates through the external cortex and into the cancellous bone, accompanied by a polished osseous growth on the inner side.

To further characterize these anomalies, researchers utilized computerized axial tomography (CT) scanning to generate cross-sectional images of the shell plates. The CT scans revealed the internal morphology of the lesions, showing hyperdense bone regions indicative of newly formed tissue during the healing process. In the case of the circular erosion, the images displayed a subcircular shape with a relatively flattened base. The variations in bone density observed in the scans suggest different stages of healing, with some areas showing more advanced restoration of physical and mechanical properties. This detailed imaging allowed the researchers to confirm that the bone growth was a biological response to the injury rather than a post-mortem alteration.

Based on the size, morphology, and distribution of the marks, the study attributes the erosions on the Eochelone brabantica shell to the activity of epibiotic organisms, specifically barnacles. Barnacles are known to attach to the shells of marine turtles, and their anchoring structures can penetrate the bone, causing lesions that range from shallow pits to deep holes. The smooth internal surfaces and well-defined but irregular margins of the fossil marks are consistent with the damage caused by barnacle attachment. The presence of both small pits and deep perforations suggests that the turtle hosted barnacles at various stages of development, with the larger lesions likely resulting from mature organisms that had sufficient time to grow and cause significant stress to the host.

The second specimen, Puppigerus camperi, exhibits a different set of shell alterations, including a healed fracture and abnormal erosion in the posterior region of the carapace. The healed fracture extends from the left ninth peripheral plate toward the center of the shell, resulting in the partial loss of several plates. The smooth and irregular contour of the fracture indicates that the turtle survived the initial trauma and underwent a healing process. The study suggests that this injury was likely caused by some form of physical trauma, such as a collision or a predator attack, although the absence of specific tooth marks or mechanical deformations makes it difficult to pinpoint the exact cause. The fact that the fracture did not involve the spinal column suggests that the injury was not immediately fatal, allowing the turtle to continue its life and heal the damage.

In addition to the healed fracture, the Puppigerus camperi carapace displays several superficial marks, including pits and linear grooves scattered across the surface. These marks do not penetrate the external cortical bone layer and are therefore not associated with bone remodelling, making it difficult to determine whether they were inflicted during the turtle’s lifetime or after death. The pits, measuring approximately 0.2 centimeters in diameter, are consistent with the activity of small invasive barnacles or post-mortem invertebrate activity. The linear grooves, which are about 2.5 centimeters long and 0.5 centimeters wide, have a U-shaped profile and smooth contours, characteristics often associated with organic processes during the postmortem interval, such as solution marks made by plants or microorganisms.

The study highlights the importance of distinguishing between premortem and post-mortem shell modifications in paleontological research. By using the presence of bone remodelling as a criterion, researchers can more accurately identify the types of interactions that occurred in ancient marine ecosystems. The findings from this study provide valuable insights into the health and behaviour of Eocene sea turtles, as well as the nature of their relationships with other organisms. The ability to identify specific agents, such as barnacles, responsible for shell damage enhances our understanding of the ecological dynamics that shaped these ancient environments.

Furthermore, the detailed examination of these fossils contributes to the broader field of paleopathology, which seeks to understand disease and injury in extinct organisms. The combination of macroscopic observation, CT scanning, and 3D surface scanning offers a powerful toolkit for analyzing fossil remains and uncovering the history of life on Earth. The results of this study demonstrate that even in the fossil record, subtle details can reveal significant information about the biology and ecology of ancient animals. As researchers continue to develop new techniques for analyzing fossils, the potential to reconstruct past ecosystems and understand the evolution of marine life will only continue to grow.

In conclusion, the analysis of bioerosional marks on the shells of Eochelone brabantica and Puppigerus camperi provides a compelling case study in the interactions between ancient marine organisms and their environment. The evidence of barnacle attachment and traumatic injury offers a window into the challenges faced by sea turtles in the middle Eocene, highlighting the complexity of their ecological niche. This study not only advances our knowledge of these specific taxa but also contributes to the broader understanding of bioerosion and its role in shaping the fossil record. By integrating multiple analytical methods, researchers have been able to provide a nuanced interpretation of the shell anomalies, offering a clearer picture of life in the ancient seas of Belgium.

Subject of Research: Bioerosional marks and paleopathology in middle Eocene sea turtle fossils from Belgium

Article Title: Bioerosional marks in the shells of two sea turtle taxa from the middle Eocene of Belgium

Article References: Guerrero, A., Smith, T., & Pérez-García, A. (2025). Bioerosional marks in the shells of two sea turtle taxa from the middle Eocene of Belgium. Fossil Record, 28(1), 45-56. https://doi.org/10.3897/fr.28.141743

Image Credits: AI Generated

DOI: 10.3897/fr.28.141743

Keywords: sea turtles, Eocene fossils, bioerosion, paleopathology, barnacles, marine ecology, Belgium, CT scanning, shell damage, ancient marine environments, Bioerosional, marks