Bones recovered from underwater caves offer a rare window into the distant past. However, scientists have had limited tools for determining how extinct megafauna and other animal remains entered these submerged environments, survived over time, and changed after burial.
A new study led by Griffith University has developed a framework for interpreting the evidence preserved on animal bones from underwater cave systems.
Uncovering the Preservation Signatures of Underwater Cave Bones
“By analyzing animal bones from two underwater cave systems in South Australia, we have revealed how different cave environments leave distinct preservation ‘fingerprints’ on skeletal remains,” said Meg Walker, a PhD candidate supervised by Australian Research Centre for Human Evolution Director Professor Julien Louys.
“Using radiocarbon-dated bones, we tracked how skeletons accumulated and were modified over decades and centuries in underwater caves, then compared them with remains buried in dry caves.
“We used a range of analytical methods, from large-scale observations to microscopic testing, to identify features associated with wet and dry cave environments.
“These included the spatial distribution of bones and surface damage, as well as elemental compositions and proteins preserved inside ancient cells.”
The analysis found that underwater caves can preserve animal bones exceptionally well. In many cases, the remains retained their original structure and finely detailed surface features.
At the same time, submerged cave environments left distinctive chemical and biological signatures on the bones. The evidence varied depending partly on the amount of light reaching each area and the organisms living in the water.
How Light and Algae Affect Cave-Bone Preservation
Near brightly lit cave entrances, algae and other aquatic plants grew in the water. These organisms sometimes colonized bone surfaces, leaving recognizable marks that can help researchers identify how the remains were preserved.
Conditions changed dramatically in the deepest, lightless sections of the caves. Without sunlight, plants could not grow, and bones in these areas often remained remarkably pristine.
Bones from dry caves showed a different pattern of alteration. They lacked the aquatic signatures found on submerged remains. Instead, land-based bacteria consumed parts of the bones, while plant roots created long grooves across their surfaces.
Animal Bones From South Australian Underwater Caves
Walker and her colleagues examined historical animal bones from Green Waterhole and Gouldens Sinkhole, two underwater cave systems near Mount Gambier in South Australia. The research team also included specialist cave divers from the Cave Divers Association of Australia.
The remains came from native and introduced species, including cows, kangaroos, emus, sheep, pigs, dingoes, rabbits, possums, quolls and swamp rats. Some specimens may date to the arrival of the first Europeans and the establishment of the city during the 1840s.
By studying how these relatively recent bones were deposited and altered, the researchers sought to better understand how fossils of extinct megafauna may have entered underwater caves. The evidence may also help reconstruct the environmental conditions surrounding those ancient remains.
A New Framework for Studying Megafauna Fossils
“This study has delivered the first framework for interpreting how megafauna fossils formed, survived and changed in underwater caves,” Walker said.
“It will provide archaeologists and paleontologists worldwide with a powerful new tool for reconstructing past environments and histories in these challenging conditions.”
The study, titled “Neotaphonomic characteristics of vertebrate site formation in underwater caves,” has been published in PLOS One.
Source: www.sciencedaily.com