Bone 'fingerprints' unlock hidden stories of underwater caves

New research reveals that bones found in underwater caves can act as "fingerprints" revealing crucial information about the environment and history of the sites where they are discovered. The study, conducted by Griffith University and published in PLOS One, shows that the unique conditions within underwater caves preserve bones in remarkable detail while leaving distinctive chemical and biological marks. This discovery offers scientists a groundbreaking method to interpret the past through the analysis of skeletal remains in such environments. Meg Walker, a Ph.D. candidate at Griffith University, led the research alongside Professor Julien Louys, director of the Australian Research Center for Human Evolution. Their work focused on two underwater cave systems in South Australia, Green Waterhole and Gouldens Sinkhole, near Mount Gambier. These caves contain a mix of native and non-native animal bones, some potentially dating back to the earliest days of European settlement in the region during the 1840s. By examining these remains, the team aimed to uncover how extinct megafauna fossils might have arrived in similar underwater settings and under what environmental conditions. The study employed a variety of analytical techniques, ranging from macro-level observations of bone distribution and surface features to microscopic analyses of elemental composition and proteins trapped in ancient cells. Researchers noted that bones in underwater caves were often exceptionally well-preserved, retaining structural integrity and surface details. However, these same environments introduced unique chemical and biological markers influenced by factors such as light exposure and the presence of aquatic organisms. In areas of the caves where light penetrated, such as near the entrances, different types of algae and plants grew on the bones, leaving identifiable traces. In contrast, deeper sections of the caves, known as "midnight zones" due to the absence of light, showed no signs of such organic growth, preserving the bones in a more pristine state. Dry caves, on the other hand, lacked these aquatic influences. Instead, bones found there exhibited damage caused by land-based bacteria and plant root activity, which created long grooves on the surfaces. The findings suggest that the differences in preservation between wet and dry caves can serve as indicators of the environmental conditions present when the bones were deposited. For instance, the presence of certain algal or plant residues could signal whether a bone was once exposed to light or submerged in water for extended periods. Such insights allow researchers to reconstruct the processes that led to the accumulation and modification of skeletal remains over time. The study provides the first comprehensive framework for understanding how megafauna fossils form, survive, and change in underwater cave environments. This framework equips archaeologists and paleontologists with a novel tool to decode the complex histories of these challenging locations. The implications extend beyond Australia, offering global researchers a standardized approach to interpreting similar fossil records in underwater caves elsewhere. The research team included specialists from the Cave Divers Association of Australia, who played a critical role in retrieving the historical animal bones from the underwater caves. The collection featured a diverse array of species, both native and introduced, reflecting the ecological shifts that occurred following European colonization. Some of the bones may predate the establishment of the city of Mount Gambier, providing valuable data on the transition from indigenous ecosystems to those shaped by human activity. As the scientific community continues to explore the potential of underwater caves as repositories of ancient history, this study opens new avenues for understanding the interplay between geological, biological, and anthropological factors. The detailed methodology developed by Walker and her colleagues sets a precedent for future investigations into the preservation of biological material in submerged environments, enhancing our ability to piece together the intricate narratives embedded in these natural archives.