In 1850, a British scientist named Samuel Stutchbury made an unusual discovery. While exploring a fossil site near Bristol, England, he found a large cylindrical bone fragment.

Since then, similar bone pieces have been uncovered in different places across Europe, including parts of Germany and France.

Over 200 million years ago, the areas where these bones were found were covered by a vast ocean. Various marine and coastal creatures that lived there left their remains buried in the sediment over time. Scientists are still debating which animal the large fossilized bones came from.

The animals could have reached 25 to 30 meters in length
The animals could have reached 25 to 30 meters in length. Credit: Marcello Perillo / University of Bonn

When Stutchbury first studied the bones, he thought they may have belonged to an extinct reptile-like land animal called a labyrinthodont. But other researchers questioned this idea.

Some proposed the fossils could be from long-necked dinosaurs, armored plant-eating dinosaurs, or an unknown dinosaur group.

In the early 1900s, some hypothesized the fossils were actually from a giant sea animal called an ichthyosaur. A young scientist named Marcello Perillo recently investigated this possibility for his master’s thesis. He examined the bones’ microscopic structure under Professor Martin Sander at the University of Bonn in Germany.

It is likely that the bones come from the lower jaw of a gigantic ichthyosaur that lived more than 200 million years ago. This is indicated by their characteristic microstructure
It is likely that the bones come from the lower jaw of a gigantic ichthyosaur that lived more than 200 million years ago. This is indicated by their characteristic microstructure. Credit: Marcello Perillo / University of Bonn

Perillo took samples of bones that had not been identified. He compared pieces from England, France, and Germany. They all showed similar distinctive properties, suggesting they came from the same animal.

Under a specialized microscope, he found the bones had an unusual wall structure containing mineralized collagen fibers woven together in a unique pattern not seen before.

Interestingly, large ichthyosaur fossils from Canada displayed a very similar bone structure. However, Perillo did not find this structure in other fossil groups he studied. This strongly indicated the pieces also belonged to an ichthyosaur, contradicting the idea they were from a land dinosaur.

With a modified drill, the researchers were able to extract pieces of the bone - without destroying the valuable fossils. The resulting thin cross-sections of bone allow the microstructure to be examined
With a modified drill, the researchers were able to extract pieces of the bone – without destroying the valuable fossils. The resulting thin cross-sections of bone allow the microstructure to be examined. Credit: Deborah Hutchinson / Bristol Museum and Art Gallery

The fossils most likely came from the lower jaw of a sea creature. By comparing their sizes to other ichthyosaur jaws, Perillo estimated the animals could have reached lengths of 25 to 30 meters, as early researchers first proposed. However, he acknowledged this is just an estimate without more complete fossils. Still, they were clearly extraordinarily massive.

Ichthyosaurs first appeared in oceans around 250 million years ago. Some grew to whale-size even then, but the largest varieties did not emerge until 215 million ago.

Nearly all ichthyosaur species disappeared over 200 million years ago at the end of the Triassic period. The unusual bone composition may have provided strength and allowed swift growth, adapting the animals for feeding and hunting in Jurassic seas.

The animal from which these fossilized bones came from was unclear for a long time - The new study now indicates that they came from ichthyosaurs
The animal from which these fossilized bones came from was unclear for a long time – The new study now indicates that they came from ichthyosaurs. Credit: Marcello Perillo / University of Bonn

Sources

Universität Bonn | Marcello Perillo, P Martin Sander. The dinosaurs that weren’t: osteohistology supports giant ichthyosaur affinity of enigmatic large bone segments from the European Rhaetian. PeerJ, 2024; 12: e17060 DOI: 10.7717/peerj.17060

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