Fossilised regurgitation masses discovered beneath the North Sea reveal that 160-million-year-old plesiosaurs swam into shallow river deltas to vomit indigestible prey remains. According to researchers, the Jurassic marine reptiles digested softer tissues and expelled hard shell clumps, mirroring modern marine behaviors observed in seals and crocodiles.
Fossilized Vomit Discovered Beneath the North Sea
For three decades, palaeontologist Dr Dirk Knaust examined thousands of metres of rock cores recovered during drilling operations for an offshore CO2 storage site near Norway’s Troll gas field for Equinor ASA. Within those Jurassic rock samples, Knaust identified more than 20 unusual fossilised masses ranging from the size of a walnut to a mango. These clusters, known scientifically as regurgitalites, contained a dense mix of bivalves, serpulid worms, crinoids, and belemnites, alongside occasional fragments of ancient plants.
The clustering and internal condition of these specimens separated them from ordinary shell accumulations formed by storms or animal burrows. The material showed signs of corrosion consistent with digestive fluids, while lacking the chemical composition typical of fossilised faeces. Similar to how modern owls cough up compact pellets of bone and fur after digesting prey, ancient marine predators left behind compressed shells coated in protective mucus.
Why Plesiosaurs Swam Ashore to Regurgitate
The location of these fossilised deposits presents an ecological puzzle reported by Zmescience. Many of the clumps were recovered from ancient river-delta deposits where incoming freshwater constantly altered the salinity. However, organisms such as crinoids and tube-dwelling worms required stable, salty marine conditions to survive and could not have lived in large numbers within the delta.
Dr Knaust concluded that the predator must have hunted these species in deeper, more stable waters offshore before swimming toward the coast. Plesiosaurs may have come close to shore to relax or sleep after hunting, and that’s likely when they vomited,
the Daily Mail noted of the researcher’s findings.
“We see fur seals and marine crocodiles doing something similar today but while they go onto land, plesiosaurs probably remained submerged due to their weight and shape.”
Dr Dirk Knaust, palaeontology expert for Equinor ASA
Ruling Out Alternative Jurassic Predators
Small predators like fish and cephalopods were ruled out because the regurgitated masses were simply too large. Jurassic sharks and crocodiles primarily hunted fish rather than grazing on seafloor shellfish, and the samples contained no fish skeletal remains.
These long-necked marine reptiles possessed teeth specialized for gripping prey rather than crushing hard shells. After consuming molluscs and sea lilies from the seafloor, their stomachs compacted the indigestible remains into oral rejections.
Preservation Alongside Dinosaur Footprints
Most regurgitated pellets would normally have broken up quickly under the action of waves and tides. The North Sea specimens survived because river sediments rapidly covered some clusters, while others settled into crustacean burrows on the seafloor where they underwent partial fossilisation.
The shallow delta environment also hosted land animals.
“There has been a lot of research into fossilised vomit over the last decade but most of it has focused on vertebrates eating other vertebrates. This is the first time that plesiosaur vomit, and the shellfish in it, have been identified, and these creatures tell us a great deal.”
Dr Dirk Knaust, palaeontology expert for Equinor ASA