Bone 'Fingerprints' from Underwater Caves and What They Teach Lowcountry Divers

One of the questions I get asked most often on the docks isn't what a fossil is, but how it got there. A megalodon tooth resting in a gravel lag on the bottom of the Cooper River, a whale vertebra tumbled smooth in the Edisto, a mammoth tooth crusted in dark river patina — every one of these arrived at its resting place through a long chain of burial, erosion, transport, and chemistry. That chain is the science of taphonomy, and a new study out of Australia has just sharpened the tools we use to read it in waterlogged settings.

What the researchers actually did

Published in PLOS One and led by Griffith University Ph.D. candidate Meg Walker under Professor Julien Louys, the study set out to establish what the team calls a set of preservation "fingerprints" for bones that come to rest in underwater caves. Working with specialist divers from the Cave Divers Association of Australia, the researchers recovered animal bones from two flooded cave systems near Mount Gambier in South Australia — Green Waterhole and Gouldens Sinkhole.

The bones weren't ancient megafauna. They belonged to a mix of native and introduced animals: cattle, sheep, pigs, kangaroos, emus, dingoes, rabbits, possums, quolls, and swamp rats. Some of these remains, radiocarbon-dated, may reach back to the first European settlement of the region in the 1840s. That recent age is the whole point. By studying bones whose accumulation history is comparatively well constrained — a discipline sometimes called neotaphonomy — the team built a reference framework they can then apply to far older, far more mysterious fossil accumulations of extinct megafauna in similar flooded caves.

The fingerprints themselves

The findings, as the researchers describe them, were strikingly clear. Underwater caves often preserve bone beautifully — surface detail, structure, and even proteins locked in ancient cells can survive in remarkable condition. But the water leaves its own marks. Near bright cave entrances, algae and aquatic plants colonized the bone surfaces, leaving distinctive biological and chemical signatures. Deep in the lightless "midnight" zones where nothing photosynthetic can grow, bones stayed pristine.

Dry caves told a completely different story. There, the researchers report, bones were attacked by soil bacteria and scored by long grooves where plant roots had grown across them. The team worked across scales — from mapping how bones were distributed in space, down to elemental composition and the proteins trapped inside — to separate the wet signals from the dry ones. The result is what Walker describes as the first framework for interpreting how megafauna fossils formed, survived, and changed inside underwater caves.

Why this matters on the Cooper and the Edisto

South Carolina doesn't have flooded limestone cave systems full of Ice Age skeletons the way South Australia does. But the deeper principle — that a submerged setting stamps a recognizable, readable signature onto bone — is directly relevant to how we collect here. The Lowcountry's richest fossil grounds are underwater: the blackwater rivers of the coastal plain, where the Cooper, Wando, Ashley, and Edisto have cut down into fossil-bearing Oligocene and Miocene marine units and concentrated the reworked material into gravel lags on the bottom.

Anyone who has held a river-recovered fossil next to a land-dug one already knows these environments leave fingerprints. Cooper River shark teeth famously come up with a deep, glossy river stain and, often, algal and biofilm growth on their surfaces. Whale bone and land-mammal material picked out of the current is frequently rounded, polished, and mineral-darkened in ways that a specimen quarried from dry sediment simply isn't. What the Australian study does is put that intuition on a rigorous footing: light-exposed submerged surfaces attract living films that modify the bone, while sheltered or buried material can remain far cleaner. That is exactly the contrast a Hobby Diver notices between a tooth lying exposed in the current and one freshly eroding from a clay ledge.

Reading the lag, not just grabbing the tooth

There's a practical takeaway buried in all this for collectors who care about more than just filling a bag. A megalodon tooth or a Carcharodon hastalis blade sitting on a Cooper River gravel bar has usually been through at least two lives: it eroded out of an older formation, then it was reworked, transported, and reconcentrated with material of very different ages. That is why a single river lag can mix Oligocene whale and shark material from the Chandler Bridge and Ashley formations with Pleistocene mammoth and mastodon remains from much younger deposits. The staining, polish, and surface biology aren't just cosmetic — read carefully, they carry information about how long a specimen sat exposed, whether it was buried and re-exhumed, and what kind of water it rested in.

The Griffith team's larger ambition is to reconstruct past environments and histories from remains in "challenging conditions." Blackwater diving is nothing if not challenging conditions — near-zero visibility, current, and depth. The lesson isn't that we should be doing lab-grade elemental analysis on every find, but that the state of a fossil is itself data. When collectors note where a piece was found, what it was found with, and how it's preserved, they're preserving a scrap of the taphonomic story that a study like this one is built to decode.

The bigger picture

What I like about this research is that it treats bones from the 1840s as a Rosetta Stone for reading bones from the Pleistocene. That's smart science: constrain the recent, then reach into the deep past. For the Lowcountry, where so much of our record was assembled by rivers doing the same sorting, mixing, and staining work over and over, it's a useful reminder that a fossil's condition is a document. The megalodon tooth in your hand didn't just fall out of the sky into the Cooper — and increasingly, careful science can tell us how it got there.