Bristol’s marine reptile mystery solved

Bristol’s marine reptile mystery solved


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Restoration of Pachystropheus rhaeticus, pictured next to a fish-eating Hybodon shark from Bilgeria. Photo by James Ormiston

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Restoration of Pachystropheus rhaeticus, pictured next to a fish-eating Hybodon shark from Bilgeria. Photo by James Ormiston

Experts discovered that some of the remains were in fact those of a fish, finally revealing the true identity of a local prehistoric marine reptile.

Now scientists from the Universities of Bristol and Southampton have revealed that bones discovered in Triassic rocks in 1935 represent one of the last thalattosaurs, large marine lizards that behaved like otters.

For many years, this ancient animal was thought to be a type of the first choristoderean, another group of marine reptiles similar to crocodiles. Journal of Vertebrate PaleontologyThe research team examined the original specimen, discovered in 1935.

They compared this to a remarkable new specimen of Pachistropheus, known as Annie, which contains hundreds of bones from several individuals, as well as evidence of sharks, bony fish and even land dinosaurs.

Jacob Quinn, a MSc student in Palaeontology at the University of Bristol’s School of Geosciences, took both specimens to Southampton where they underwent a CT scan, which produced a stack of X-ray pictures that went through the block and allowed him to reconstruct a complete 3D model of everything that was buried within it.

“Thalattosaurs were around throughout the Triassic Period,” Jacob explains. “Some reached lengths of up to four metres (13 feet) and would have been terrors of the seas. But our Pachystropheus was only one metre long, half of which was its long tail. It also had a long neck, a tiny matchbox-sized head (which has yet to be found) and four paddles. If Pachystropheus was like its kin, it would have had lots of sharp little teeth that would have been ideal for catching fish and other small, mobile prey.”

“Until now, Pachystropheus had been identified as the first of another group of crocodile-like marine reptiles, the Choristoderes, and was held in great importance because it was the oldest,” said Professor Mike Benton, one of Jacob’s supervisors.

“Jacob was able to prove that some of the bones were in fact fish-like, and other bones that belonged to Pachystropheus showed that it was in fact a small thalattosaur. So Pachystropheus, which was thought to be the first of the choristoderes, has now been identified as the last of the thalattosaurs.”


The holotype specimen of Pachystropheus rhaeticus (NHMUK PV R 747): A, complete specimen; B, CT-scanned parts; C, photograph; D, CT-generated 3D surface image. Credits: Journal of Vertebrate Paleontology (2024). DOI: 10.1080/02724634.2024.2350408

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The holotype specimen of Pachystropheus rhaeticus (NHMUK PV R 747): A, complete specimen; B, CT-scanned parts; C, photograph; D, CT-generated 3D surface image. Credits: Journal of Vertebrate Paleontology (2024). DOI: 10.1080/02724634.2024.2350408

Evangelos R. Massaud Raven, from Peterborough, discovered Annie whilst on holiday in Somerset in 2018, and used his spare time to painstakingly reassemble and clean her until the bones were exposed. “I found a piece of rock that had fallen on the beach, about 10 metres from the base of the cliff, and I was really excited to see some fossilised bones on the exposed surface,” Mr Massaud said.

“It wasn’t until a few days later that I saw the pieces, collected two days apart, coming together. After weeks of preparation, I knew something special was on the way.”

“It took about 350 hours and about a year to complete the specimen.”

“Pachystropheus probably lived a similar lifestyle to modern otters, feeding on small fish, shrimp and other invertebrates,” said Dr David Whiteside, another of the study’s authors.

“This slender reptile had a long neck, a flattened tail for swimming and surprisingly strong forelimbs for a marine animal, which suggests that Pachystropheus may have come onto land to feed or to avoid predators. At the time, the seas around Bristol, and much of Europe, were shallow, and these animals may have lived in large colonies in the warm, shallow waters surrounding islands.”

Annie will now be housed at Bristol Museum and Art Gallery for further study.

“We are delighted that this incredible fossil has become part of Bristol Museum and Art Gallery’s collection, thanks to the kind assistance of our friends at Bristol Museum, Art Gallery and Archives.

“We’re thrilled to be able to share the story of this new fossil and all the work the team has done with museum visitors,” says Deborah Hutchinson, Curator of Geology at Bristol Museum and Art Gallery.

For more information:
Jacob G. Quinn et al. “Phase relationships and paleoecology of the enigmatic Late Triassic marine reptile Pachystropheus rhaeticus (Diapsid: Thalattosaurinae)” Journal of Vertebrate Paleontology (2024). DOI: 10.1080/02724634.2024.2350408

Journal Information:
Journal of Vertebrate Paleontology



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