Fossilized Plesiosaur Vomit Reveals Ancient Feeding and Coastal Behavior

Paleontologist Dirk Knaust was examining drill cores from beneath the North Sea when he encountered something most scientists would regard as an unlikely prize: fossilized vomit. More than twenty of these preserved masses, technically called regurgitalites, had survived millions of years buried in sediments from an ancient river delta. Inside them lay the shells of marine creatures—bivalves, serpulid tubes, crinoids, belemnites—the hard remains of animals that could not be digested.

The puzzle was geographical. These shells belonged to organisms that thrived in the open ocean, creatures requiring the stable salinity of deeper water. Yet the fossils lay in sediments deposited by a river delta during the Jurassic period, where freshwater would have made conditions inhospitable for such marine life. The mismatch suggested a single explanation: something large had eaten these creatures far offshore, then traveled to shallower coastal waters before expelling what its body could not process. Knaust's research, published in Geological Magazine in September 2026, points to plesiosaurs as the source.

Identifying the culprit required careful elimination. The pellets contained no fish skeletons, ruling out sharks and crocodiles, which fed primarily on fish during the Jurassic. Cephalopods were too small to account for the size of the masses—some measured at least ten centimeters across. Fish themselves produced regurgitated material far too small. Plesiosaurs, by contrast, matched both the scale and the feeding profile. Knaust focused specifically on cryptoclidid plesiosaurs, creatures that grew four to eight meters long and roamed the seas from the Middle Jurassic through the Early Cretaceous, roughly 174 to 100.5 million years ago.

The discovery offers rare direct evidence of how these marine reptiles actually hunted and moved through their world. Previous research suggested plesiosaurs fed near the seafloor, their long necks and downward-angled heads suited to collecting prey, their teeth designed for gripping rather than crushing. But the vomit tells a behavioral story: these animals likely gathered food in deeper water, then swam into sheltered coastal zones—perhaps to rest or sleep—before regurgitating the indigestible shells. Modern fur seals and marine crocodiles exhibit similar patterns, though they haul out on land; plesiosaurs, constrained by their weight and body shape, probably remained submerged.

Preservation itself was improbable. Most regurgitated material would have been destroyed by waves and tides, scattered and broken into nothing. These pellets survived because they were compacted and coated in mucus, then either rapidly buried by river sediment or swept into crustacean burrows on the seafloor, where they fossilized in place. The drill cores came from a site now about fifty kilometers off the Norwegian coast, in rocks that once formed a shallow delta during the Jurassic. Dinosaurs walked the nearby land surfaces; their footprint fragments appear in the same drill core record.

Knaust's work opens a window onto behavior that may have been widespread. Plesiosaur fossils are found worldwide, with Britain preserving particularly rich deposits. During the Jurassic, the North Sea site and rocks now exposed along southern England were part of the same narrow marine region. If plesiosaurs in Norwegian waters exhibited this feeding and resting pattern, similar behavior likely occurred around ancient British coastlines and beyond. The vomit, preserved by chance and read with precision, reveals not just what these creatures ate but how they lived—hunting in the deep, retreating to the shallows, their bodies and behaviors shaped by the demands of a world that vanished 66 million years ago.