Jurassic Sea Monsters May Have Swum to Shore to Vomit

A pile of fossilized puke is revealing how Jurassic sea monsters may have hunted and fed

Some cats have a peculiar talent for racing past every easy-to-clean surface in the house, only to throw up on the carpet or bed. As it turns out, some Jurassic sea monsters may have had their own preferred place to puke.

Roughly 160 million years ago, long-necked marine reptiles called plesiosaurs may have also swum towards shallow coastal waters to regurgitate the shells and other indigestible remains of their meals.

Now, scientists have found what they believe is their fossilised vomit beneath the North Sea. It must have been a gross pile back in the day, but now it is offering an unexpectedly detailed glimpse into how the animals hunted, what they ate, and where they went after feeding.

A prehistoric meal buried beneath the North Sea

Funny enough, the study didn’t start with a hunt for ancient marine reptiles, but rather with rock samples collected during drilling operations in the North Sea.

For three decades, palaeontologist Dirk Knaust, who works for the Norwegian energy company Equinor, has examined thousands of metres of rock cores recovered from beneath the seabed. The samples correspond to the Jurassic period, when much of what is now the North Sea was a network of shallow marine waters, river deltas, and coastal habitats.

Time and time again, Knaust kept finding some unusual bits of fossil material.

Not all were the same. Some contained broken seashells. Others held the remains of tube-dwelling marine worms or crinoids, marine animals related to modern starfish and sea urchins. Fragments of ancient plants occasionally appeared among the shells.

The clusters usually measured just a few centimeters across, but they didn’t seem to make sense together. No matter how Knaust tried to compare the species, shape, and geological surroundings, it just didn’t add up.

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Then, he found a surprising explanation: these weren’t ordinary accumulations of dead marine animals. Something had eaten them first.

Fossilized vomit

The key clue came from how the shells were packed together. Storms usually sweep shells into piles, while burrowing animals can redistribute them through the sediment. But the clusters Knaust was looking at were different.

For starters, they were tightly packed. Some showed signs of corrosion, which is consistent with digestive fluids altering them. Their irregular shapes and the abundance of largely undigested material also distinguished them from fossilised faeces, which often have a different chemical composition.

Knaust concluded that the clusters most likely represented regurgitated material, known scientifically as regurgitalites.

The closest modern comparison is an owl pellet. Owls swallow their prey, digest the nutritious parts, and cough up compact masses of indigestible bones and fur. Birdwatchers looking for owls often also scout the ground for such accumulations.

The Jurassic fossils appear to preserve a similar process, except that their contents consisted largely of shells and other hard remains from marine animals.

Why would a sea monster vomit near shore?

Of course, we know very little about plesiosaur behavior, particularly when it comes to vomiting. But Knaust’s theory has another argument backing it up: location.

Many such clusters occurred in ancient river-delta deposits, environments where incoming freshwater would have repeatedly changed the saltiness of the water. Yet some of the animals preserved inside the clusters, including certain crinoids and tube-dwelling worms, required more consistently salty marine conditions.

This suggests they were brought from the sea into the delta.

Knaust’s theory is that a predator collected these animals while feeding farther offshore, then moved towards the coast and regurgitated their indigestible remains. The presence of terrestrial plant fragments adds another intriguing detail. The predator may have swallowed bits of plant material alongside animals living on or near the seabed.

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It’s not clear why a Jurassic sea creature would have done this. The behaviour may have formed part of its normal feeding routine rather than a deliberate trip to dispose of stomach contents. But modern marine mammals offer possible parallels. Fur seals and dolphins can regurgitate indigestible material after feeding.

Even figuring out who did this is a challenge. The fossil clusters don’t contain any teeth or evidence that could be used as a diagnostic.

Knaust considered several potential candidates, including ancient sharks, marine crocodile relatives, and plesiosaurs. His main suspects are the cryptoclidids, a family of long-necked plesiosaurs that lived from the Middle Jurassic into the Early Cretaceous.

Some of them reached lengths of four to eight meters, and had small heads and long necks that helped them collect prey from the seabed. Unlike animals equipped with powerful shell-crushing teeth, these plesiosaurs could have swallowed some hard-shelled prey without thoroughly breaking it apart.

An unlikely new window into Jurassic life

Knaust formally described the findings, splitting them into three new types of trace fossils. He distinguishes clusters dominated by mollusc shells, tube-worm remains, and crinoid fragments.

Trace fossils are useful because they preserve evidence of an organism’s activity rather than its body. Footprints, burrows, and fossilised digestive waste can all reveal behaviours that skeletons alone cannot reconstruct.

The findings also suggest that similar fossils could be hiding in existing geological collections, overlooked as ordinary accumulations of broken shells.

For an animal that disappeared more than 66 million years ago, even its discarded dinner could have a remarkable story to tell.

Journal Reference: Dirk Knaust (2026), The fate of supposed plesiosaur vomit from Jurassic delta deposits offshore Norway, Geological Magazine, 163, e43. Published September 23, 2026.