Oil Drillers Stumble Upon 160-Million-Year-Old Sea Monster Vomit

Roughly 160 million years ago, a long-necked sea reptile cruising the shallows off what is now Norway opened its mouth and heaved up everything it couldn’t stomach: a slurry of broken shells, worm tubes and waterlogged wood. That sloppy mouthful settled into the mud, hardened into stone, and sat untouched until an oil crew drilling for petroleum and carbon-storage sites hauled it back to the surface.

A scientist working for the Norwegian energy company Equinor spent decades examining core samples, the long cylinders of rock brought up from deep wells, and kept noticing strange little clumps packed with broken shells, worm tubes and tiny plant fragments. Those clumps didn’t look like anything waves or currents naturally deposited. They looked like something had eaten a meal, failed to digest parts of it, and thrown the rest back up.

That hunch became the basis of a new study published in Geological Magazine, which argues these clumps, ranging in size from a walnut to a mango, are fossilized vomit, technically known as regurgitalites, most likely produced by a group of long-necked, small-headed sea reptiles called plesiosaurs. It makes for an odd kind of evidence: a hard record of what an ancient sea monster ate, and where it stopped to bring it back up.

How Oil Drilling Cores Turned Up Ancient Fossil Vomit

Most fossil discoveries come from cliffs, quarries or riverbanks, where erosion exposes old rock. This one came from somewhere far less picturesque: continuous rock cores drilled from wells in the Troll oil and gas field area, offshore Norway, as part of routine energy exploration and carbon storage work. Those cores cut through rock layers dating from about 168 million to roughly 155 million years ago, when the area was a river delta system dumping sand and mud into a shallow sea.

Norwegian geologist Dirk Knaust closely examined about 20 to 30 clumps, though the exact count is fuzzy because many had broken down over time. High-resolution scans, borehole images, and detailed photographs allowed Knaust to examine each clump layer by layer, checking how the shells and other fragments were packed together.

These clumps kept turning up in one spot: the front edge of ancient river deltas, where freshwater flowing off the land mixed with salty ocean water. That location became a major clue. Many of the creatures packed inside the clumps, including tube worms and sea lilies called crinoids, can only survive in steady, fully salty ocean water. Finding them clustered in a zone where the water constantly shifted between salty and fresh didn’t make sense, unless something had carried them there from elsewhere and dropped them off.

Ruling Out Poop, Burrows and Storm Debris

Before calling anything vomit, the study had to rule out several look-alikes. Storms naturally pile sediment into shell-packed layers, and burrowing animals can dig tunnels stuffed with shell fragments that look similar when sliced open. The clumps could also have been fossilized droppings.

A few details tipped the scale toward vomit. The clumps were tightly packed rather than loosely scattered, mixed complete and broken shells of very different sizes together, and showed pitted, worn edges consistent with partial digestion. Droppings tend to have a smooth, even texture because stomach acid breaks material down uniformly. These clumps instead held a messy mix of undigested leftovers, exactly what an animal would leave behind when it couldn’t process the food. The study also compared the Norwegian samples with similar clumps found in outcrops on Jameson Land in East Greenland, an area with matching rock layers and age, and found the same mix of shell types and structure.

Tracking Down the Plesiosaur Vomit Culprit

Once vomit seemed like the best explanation, the obvious next question was whose vomit it actually was. The study worked through a list of suspects. Knaust considered squid-like creatures, but they produce different, smaller waste piles. Fish were ruled out as too small to cough up chunks this size. Sharks called hybodonts, common in the Jurassic and known for crushing teeth built for eating shellfish, stayed on the list as a possibility. Crocodile relatives were mostly ruled out, since their typical prey, fast-moving fish and squid, doesn’t match a stomach full of bottom-dwelling shellfish and worms.

That left plesiosaurs, specifically a family called Cryptoclididae, animals with long necks, small heads and rows of thin, tightly packed teeth. Fossil skeletons and stomach contents from related plesiosaurs elsewhere show they fed by sifting through mud on the seafloor for shellfish, worms, crustaceans and small sea lilies, a feeding style that lines up closely with what’s packed inside these clumps. Their necks also allowed more up-and-down movement than side-to-side swinging, another detail that fits an animal dipping its head toward the bottom rather than chasing fast prey through open water. Timing also fits: Cryptoclididae were common in the area during the same stretch of Jurassic time when these vomit clumps formed.

A vertebra from an ichthyosaur, another type of marine reptile, turned up in the same rock alongside the clumps, but the study notes ichthyosaurs mostly ate soft-bodied swimming prey like squid and fish, so it likely wasn’t the source. Fossilized droppings from crocodile relatives also appeared nearby, further evidence that a whole community of Jurassic predators was active in the area, even if the vomit itself points most strongly to the long-necked plesiosaurs.

What Plesiosaur Vomit Reveals About Ancient Sea Life

Most of this fossil vomit didn’t survive intact. River delta environments are busy, fast-changing places with lots of sediment piling up and burrowing creatures constantly churning through the mud. As a result, burrowing animals broke many clumps apart, chewed them, or slowly absorbed them into the surrounding mud, leaving only scattered fragments.

A few pellets made it through because they were durable, tightly compacted and bound by mucus when the animal brought them up. Rapid burial under river sediment helped, as did a lucky landing in burrows left by seafloor crustaceans. In some clumps, calcite slowly cemented the contents into a hard lump before scavengers or currents could scatter them. Others were dug up again by shifting currents and worn down, ending up smaller, rounder and more scattered than when they first settled. Only a fraction stayed intact enough for scientists to study today.

Because these clumps kept appearing in a recognizable form, the study formally classified them as a new type of trace fossil, a fossil that records behavior rather than the creature’s body. The clumps were named Vomitus, a straightforward nod to their contents, with three types: one dominated by shell fragments, one by worm tubes, and one by crinoid fragments. Giving them an official name gives other researchers digging through old rock cores or outcrops elsewhere in the world a defined checklist for spotting similar vomit clumps if they come across them.

What these leftovers reveal matters more than the gross-out factor. They point to a long-necked sea reptile that hunted along the muddy seafloor, then swam toward the coast to bring up what it couldn’t digest, much as fur seals and dolphins do today. Preserved by accident in rock drilled up for oil and gas exploration, that behavior hands paleontologists something stomach contents rarely can: a glimpse of what an ancient predator ate and where it traveled afterward.