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| Gastrolith from Traskasaura sandrae |
Our story begins, fittingly, in the belly of a marine reptile from Vancouver Island’s Trent River—a local who took the phrase “gut of stone” rather literally.
This polished pebble once tumbled through Cretaceous surf some 80 million years ago, only to end up as part of a Mesozoic digestive strategy.
Today, it sits fossilised and gleaming in the Courtenay Museum, a geological souvenir from an age when eating rocks was not just tolerated but recommended.
This lovely was found in the belly of a new genus and species of elasmosaur named Traskasaura sandrae, in honour of the Trask family — Mike, Pat and Heather Trask.
Gastroliths—smooth stones swallowed on purpose—were the original “multi-tools” of digestion. They turn up in the fossil record of marine reptiles like plesiosaurs and ichthyosaurs, in dinosaurs from Camarasaurus to Caudipteryx, and even in modern birds and crocodiles.
Think of them as internal food processors—helping grind up shellfish, bones, and whatever else made the Mesozoic menu.
Why rocks? Well, if you’re a giant aquatic reptile with flippers instead of forks, chewing isn’t really an option. Instead, you gulp your prey whole, toss in a few stones, and let physics do the work.
Inside the muscular gizzard, those gastroliths tumble around, mashing up food like a prehistoric smoothie blender. They also may have served as ballast, helping the reptile fine-tune buoyancy—a sort of stone-age scuba weight belt.
Of course, scientists have debated which role was more important: digestion or diving? Were these animals after smoother sailing or smoother meals? The jury’s still out, but the answer might be “both”—because why not have a rock that multitasks?
The Trent River specimen, like others from Vancouver Island’s fossil beds, is particularly well-rounded—literally. Its polished surface hints at long tumbling in surf before being swallowed, and longer wear inside a reptilian stomach before being fossilised.
Imagine being a small stone, minding your own business in the shallows, when suddenly—gulp!—you’re swept into the digestive adventures of a marine predator. Millions of years later, you emerge as a museum piece. Talk about a career arc.
Modern birds still use gastroliths, so next time you watch a chicken pecking gravel, remember—it’s not just weird farmyard behaviour. It’s a direct evolutionary link to ancient seagoing reptiles. The same survival trick that helped plesiosaurs patrol the Cretaceous seas now helps your backyard hen break down corn.
So, the next time you’re strolling along the Trent River and spot a rounded pebble, take a closer look. Could it be a river stone? Sure. But it could also be the relic of a reptilian digestive system, polished by waves, stomach acid, and time itself. Because in the fossil record, even the smallest stone can tell a story—and in this case, it’s a story of rocks, reptiles, and the enduring appeal of an all-you-can-eat buffet… with a little extra crunch.
Gastrolith Image: Outside of the field of view of this photo is Mike Trask sitting beside me telling all about the construction of the scaffolding he devised for the extraction of the elasmosaur bones.
Across the river, his twin brother Pat was covering the bones in a protective case and oodles of VIPS volunteers were getting ready for the big moment when the bones would be taken out of the cliff.
It is a bittersweet memory, as Mike has gone for his last walk in the woods and is waiting for our next adventure on the other side. I miss that man so much.
