Fossilized 'Sea Monster Vomit' Reveals Ancient Feeding Habits

Prehistoric marine reptiles known as plesiosaurs, some of the largest predators to ever inhabit the seas, may have swum to shallow coastal waters and river deltas to vomit up the indigestible parts of their meals. Scientists have uncovered fossilized remains of this "vomit," known as regurgitalites, dating back approximately 160 million years to the Jurassic or Early Cretaceous periods.

These fossilized clumps, ranging in size from a walnut to a mango, were discovered during offshore drilling for a CO2 storage site near Norway's Troll gas field. Dr. Dirk Knaust, a paleontology expert for Equinor ASA, led the study analyzing 20 pieces of these regurgitalites. He determined that the plesiosaurs likely consumed a variety of shellfish, which require stable saltwater conditions to survive.

The perplexing aspect was the location of the fossils – river deltas, where freshwater flow would make such shellfish populations impossible. Dr. Knaust's hypothesis is that the plesiosaurs consumed the shellfish in deeper, more stable marine environments and then transported them inland within their stomachs. He suggests that plesiosaurs may have approached shorelines to relax or sleep after hunting, a behavior observed in modern animals like fur seals and saltwater crocodiles.

Unlike modern counterparts, the body shape and weight of plesiosaurs likely kept them submerged in shallow waters rather than hauling themselves onto land. Evidence suggests the land itself could have posed a danger, as footprints from two-legged dinosaur predators were found imprinted on some of the fossilized vomit chunks.

The regurgitalites were able to fossilize due to their compact nature and coating of mucus, which aided preservation. While most would have been broken down by tides and waves, some were quickly covered by sediment or preserved in seafloor burrows. Dinosaur vomit and feces are highly valuable to paleontologists as they offer a direct glimpse into the animals' diets.

Dr. Knaust narrowed down the culprit by examining the types of shellfish present. The size of the regurgitalites excluded smaller predators like fish or cephalopods. Jurassic sharks and crocodiles, which primarily hunted fish, were also ruled out as they would not have ingested shellfish from the seafloor in the same manner.

This left cryptoclidid plesiosaurs, which grew four to eight meters long and lived from the Middle Jurassic to Early Cretaceous periods (174 to 100 million years ago), as the most probable source. These creatures were widespread and particularly abundant around the coasts of what is now the United Kingdom. During the Jurassic period, the Norwegian drilling site and the rock outcrops along England's Jurassic Coast were part of the same narrow sea, suggesting similar deposits of plesiosaur vomit may exist there.

Dr. Knaust noted that plesiosaurs are fascinating animals and that analyzing their fossilized digestive waste offers significant potential for further understanding extinct life.