While dinosaurs such as stegosaurs roamed the land, ichthyosaurs swam in prehistoric seas. Now, a new study documents the first fossilised vertebra from an ichthyosaur found in Denmark. The bone was discovered in a loose boulder at Lodbjerg Klint in Thy and adds to the limited record of ichthyosaurs in Scandinavia.
– Very few ichthyosaur fossils have been found in Scandinavia, and until now, no ichthyosaur fossils discovered in Denmark were known. Although we have only found a single vertebra, we can identify it as belonging to an ichthyosaur. The discovery therefore provides new insights into the presence of ichthyosaurs in the region and is an important contribution to our understanding of prehistoric marine life, says Laura Cotton, associate professor and curator of Danekræ at Natural History Museum Denmark and lead author of the study.
Previously, the only known Scandinavian ichthyosaur fossils had been discovered in Arctic Norway. The Danish discovery therefore shows that ichthyosaurs were also present farther south in Scandinavia.
The only known fossils of large marine reptiles from Denmark have been remains of plesiosaurs from Jurassic deposits on Bornholm, as well as a few finds of Cretaceous mosasaurs. The discovery of the ichthyosaur vertebra therefore adds a new group of marine reptiles to Denmark’s fossil record.
Ichthyosaurs were an extinct group of marine reptiles that inhabited the world's oceans from the Early Triassic to the Early Cretaceous. They evolved from terrestrial reptiles into highly efficient swimmers, and some species developed a body shape resembling those of modern tuna and dolphins. However, ichthyosaurs were neither fish nor dinosaurs, but a distinct group of marine reptiles.
The vertebra was found in a loose boulder on the beach at Lodbjerg Klint in Thy. The boulder may therefore have travelled a considerable distance from the place where the ichthyosaur’s remains were originally buried.
The researchers believe the boulder most likely originated from Jurassic deposits in the Skagerrak–North Sea region and was carried towards Denmark by glaciers during the Ice Age. However, the boulder’s exact origin remains unknown. The researchers were unable to date the rock’s matrix using microfossils, so their assessment is based on the appearance of the bone, the composition of the rock and the geological history of the area.
– To investigate where the boulder might have originated, we compared it with other boulders in the museum’s collections that were transported here during the Ice Age. Some of these contain Jurassic fossils and were found in the same area of the west coast of Jutland. Together with the composition of the rock and our understanding of Ice Age glacial movements, this points to the Skagerrak–North Sea region as a possible source. However, we cannot determine exactly where the boulder came from, says Laura Cotton.
The vertebra measures approximately nine centimetres across and just over eight centimetres in height. Its shape indicates that it came from the anterior to middle part of the ichthyosaur’s tail.
The researchers compared the vertebra’s measurements with those of several known Jurassic ichthyosaurs. It is larger than the vertebrae of several known ichthyosaur species that reached body lengths of up to about three metres, but smaller than those of the largest ichthyosaurs, which could grow to around ten metres in length. However, the researchers cannot determine which species the vertebra belonged to.
Fossil collector Christian Bach Hansen discovered the vertebra in 2025. In 2026, it was added to the Danekræ collection at Natural History Museum Denmark.
The study, First ichthyosaur remains from Denmark within glacial erratics, was written by Laura J. Cotton, Lotta Dreyer and Lene L. Delsett and published in the Bulletin of the Geological Society of Denmark in 2026.
