Prehistoric puke! Queasy sea monsters swam to shore to vomit, Jurassic fossils reveal

Prehistoric sea monsters had to swim ashore to vomit, a stomach–churning study has revealed.Scientists uncovered a collection of fossilised puke in what would have been the shallow waters of river deltas, 31 miles (50km) off the Norwegian coast.These ancient piles of sick date back around 160 million years to the Jurassic or Early Cretaceous period, and range from the size of a walnut to as big as a mango.According to Dr Dirk Knaust, palaeontology expert for Equinor ASA, they were left behind by plesiosaurs – some of the largest and most successful predators to ever stalk the seas.Dr Knaust told the Daily Mail: 'It can be assumed that these plesiosaurs thrived in shallow–marine coastal environments and offshore, where they used their long necks to graze for food at the seafloor, such as molluscs, sea lilies, and shallowly buried worm tubes.'These food components were collected and swallowed, but only the soft parts were digested, while the hard shelly parts became concentrated in clumps to be orally rejected.'Just like modern owls today, plesiosaurs would then vomit up the compressed remains onto the beach, where some became fossilised.However, Dr Knaust says that the strange mix of remains in these preserved pellets presents an even more perplexing prehistoric puzzle. Scientists say that queasy plesiosaurs swam to shore in freshwater areas to vomit up the remains of their meals Dr Knaust examined 20 pieces of fossilised vomit, known as regurgitalites, found during drilling for an offshore CO2 storage site near Norway's Troll gas field.He discovered that whatever had vomited up these pellets had been eating a wide variety of shellfish, which all required very stable salt levels to survive.However, the area where the vomit was found was in a river delta, where the constant flow of fresh water would have made it impossible for these animals to live in such large numbers.Dr Knaust's solution is that the shellfish were transported inland from deeper, more stable waters in the stomachs of plesiosaurs.He says: 'Plesiosaurs may have come close to shore to relax or sleep after hunting, and that’s likely when they vomited.'Today, fur seals and saltwater crocodiles are known to have a similar behaviour.'Unlike seals and crocodiles, plesiosaurs' body shape and weight meant that they likely stayed submerged in the shallows rather than dragging themselves out onto the beach.The land may have also been too dangerous, even for these big ocean predators, as researchers found the footprints of two–legged dinosaur predators printed into some of the vomit chunks. A palaeontologist found clumps of fossilised vomit (pictured) in what would have been the shallow waters of river deltas, 31 miles (50 km) off the Norwegian coast The plesiosaur pellets were able to become fossils because they were incredibly compact and coated with mucus, allowing them to survive longer.'Even so, most pellets would have been completely broken up by the waves and tides,' says Dr Knaust.'Some clusters were, however, quickly covered by sediment arriving from the rivers, and some ended up in burrows left by crustaceans on the seafloor, where they were partially preserved and fossilised.'Dinosaur vomit and faeces are extremely valuable to palaeontologists because they give a uniquely clear look at exactly what was in these animals' diets.However, that valuable insight is only possible if you can work out which animal the vomit actually came from – something which was originally a total mystery.When the preserved vomit was first discovered, Dr Knaust had no idea what might have left it.Dr Knaust was able to narrow down the possibilities by looking carefully at the type of shellfish in the pellets.The vomit pellets are simply too large to have come from any small predators like a fish or cephalopod, a group that contains squids and octopuses. The vomit contained shellfish that wouldn't have survived in those less salty waters, suggesting that they were carried closer to shore in the stomachs of roaming plesiosaurs Likewise, Jurassic sharks and crocodiles hunted fish rather than eating shellfish from the seafloor, and Dr Knaust didn’t find any evidence of fish skeletons in the fossilised vomit.That left plesiosaurs as the most likely remaining culprit.The cryptoclidid plesiosaurs, which Dr Knaust holds responsible for the vomit, grew four to eight metres long and lived between the Middle Jurassic and the Early Cretaceous periods, from 174 to 100 million years ago.They were incredibly widespread and were especially abundant around the shores of what is now the UK.In Jurassic times, the location of the well where the fossils were collected and the outcrops of rock along coastal cliffs in southern England belonged to the same narrow sea.That means England's Jurassic Coast could also be littered with its own piles of plesiosaur vomit.Dr Knaust adds: 'The plesiosaur is such a fascinating animal.'And this is still just the beginning. There’s so much more we can learn from picking through what extinct animals threw up after dinner.'