Bones recovered from underwater caves can provide an extraordinary record of the distant past. Until now, however, scientists have lacked a reliable way to determine how the remains of extinct megafauna and other animals accumulated, survived, and changed inside these submerged graveyards.
A new study led by Griffith University provides researchers with a framework for reading the evidence preserved on these bones.
Reading the Fingerprints Left on 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.
“Backed by radiocarbon-dated bones, we tracked how skeletons accumulated and were modified over decades and centuries in underwater caves, then compared them to those buried in dry caves.
“Using a range of methods, from the macro to the micro, we looked at features associated with wet and dry caves.
“Things like spatial distributions of the bones and their surfaces, down to elemental compositions and proteins trapped in ancient cells.”
The analysis showed that underwater caves can preserve skeletal remains exceptionally well. In many cases, the bones retained their original structure and finely detailed surfaces.
At the same time, submerged cave environments created distinctive chemical and biological marks. The type of evidence found on each bone depended partly on the amount of light in the surrounding water and the organisms living there.
Light, Algae, and Total Darkness
Near brightly lit cave entrances, several kinds of algae and plants grew in the water. These organisms sometimes colonized the surfaces of bones, leaving recognizable signatures behind.
Conditions were very different in the midnight regions of the caves. Because sunlight never reaches these areas, plants cannot grow there, and the bones often remained pristine.
Bones preserved in dry caves displayed a different set of changes. They lacked the aquatic signatures found on submerged remains. Instead, land-based bacteria consumed parts of the bones, while plant roots carved long grooves across their surfaces.
Animal Remains From South Australian Caves
Walker and her colleagues collected historical animal bones from Green Waterhole and Gouldens Sinkhole, two underwater cave systems near Mount Gambier, South Australia. The research team included specialist cave divers from the Cave Divers Association of Australia.
The remains came from both native and introduced animals, including cows, kangaroos, emus, sheep, pigs, dingoes, rabbits, possums, quolls and swamp rats. Some of the specimens may date back to the arrival of the first Europeans and the establishment of the city during the 1840s.
By examining how these more recent bones were deposited and altered, the researchers aimed to understand how fossils belonging to extinct megafauna may also have entered underwater caves. The evidence could also reveal the environmental conditions that surrounded those ancient remains.
A New Tool for Megafauna Research
“This study has delivered the first framework for interpreting how megafauna fossils formed, survived, and changed in underwater caves,” Miss 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 “Neotaphonomic characteristics of vertebrate site formation in underwater caves” has been published in PLOS One.