PLESIOSAUR VOMIT FOSSILS REVEAL SHELLFISH-EATING BEHAVIOUR

Fossilised plesiosaur vomit found off the Norwegian coast shows the marine reptiles swam to shore to bring up indigestible shell fragments after feeding, according to research published in Geological Magazine by Cambridge University Press. Palaeontologist Dr Dirk Knaust identified more than 20 fossilised vomit clumps, known as regurgitalites, ranging in size from a walnut to a mango, in rock that once formed the shallow waters of a river delta roughly 50 kilometres off Norway. Knaust said it is the first time plesiosaur vomit, and the shellfish remains within it, have been identified. He said extensive research into fossilised vomit over the past decade has focused mainly on vertebrates that had eaten other vertebrates, making this discovery distinct.

The shellfish found in the vomit required the stable salt levels of open ocean water to survive, yet the delta where the remains were deposited had fluctuating salinity caused by incoming freshwater, meaning the shellfish could not have lived there. Knaust concluded that the plesiosaurs must have fed on the shellfish from the seafloor in deeper water, then swum to shore to expel the hard, indigestible parts, a behaviour resembling that seen in modern fur seals and marine crocodiles. Earlier research into plesiosaur anatomy suggested the long-necked reptiles angled their heads downward to gather shellfish from the seafloor, and that because their teeth could not crush shell or skeletal material, their stomachs compacted the debris into pellets for regurgitation, as owls do today.

Knaust, who specialises in fossil traces left by invertebrates, has spent three decades analysing thousands of metres of drill core samples from North Sea wells operated by his employer, the Norwegian energy company Equinor ASA. Most of the vomit fossils examined in the study came from core samples taken during development of a subsea carbon dioxide storage site near the Troll gas and oil field. The findings add new detail to understanding of plesiosaur feeding behaviour during the Jurassic period.