Bristol marine reptile fish mystery solved

Now scientists from the University of Bristol and the University of Southampton can reveal that bones found in Triassic rocks in 1935 are one of the last Thalatosaurs, a large lizard that behaved like an otter.

For years it was assumed that the ancient animal was one of the first choristoderas, another group of crocodile-like marine reptiles. However, in the study, published today in the Journal of Vertebrate Paleontology, the team examined the original named specimen from 1935. They compared it to a remarkable new specimen of Pachystropheus, known as “Annie,” which contains hundreds of of bones from several people. , as well as evidence of sharks, bony fish and even land dinosaurs.

Jacob Quinn, who is studying for an MSc in Palaeobiology at Bristol’s School of Earth Sciences, traveled with the two specimens to Southampton where they were CT scanned, producing X-ray stacks through the blocks which allowed him to reconstruct a full 3D model of everything buried in blocks.

“Thalattosaurs were around throughout the Triassic,” explained Jacob. “Some of them were up to four meters (13 feet) long and would have been the terrors of the seas. But our Pachystropheus was only a meter long and half of that was its long tail. He also had a long, small neck. head the size of a matchbox, which we couldn’t find, and four oars. If it was like its relatives, it would have had lots of sharp teeth, ideal for ripping off fish and other small, squirming prey.

“Pachystropheus was previously identified as the first of the choristoderes, another group of crocodile-like marine reptiles, and was treated as very important because it was the oldest,” said Professor Mike Benton, one of Jacob’s supervisors. “Jacob was able to show that some of the bones actually came from fish, and the others that really belonged to Pachystropheus show that it was actually a small thalatosaur. So, once considered the first of the choristoderes, it is now identified as the last. of thalatosaurs”.

Evangelos R. Matheau-Raven of Peterborough discovered Annie while on holiday in Somerset in 2018, then carefully collected and cleaned it to expose the bones in his spare time. He said: “I noticed parts of a rock that had fallen onto the beach about 10m from the base of the cliff. I was delighted that their exposed surfaces showed some fossil bones.

“It was only after a few days that I could see that the pieces collected two days had come together. After a few weeks of preparation, I could see something special emerging.

“The specimen took me about 350 hours and about a year to complete.”

“Pachystropheus probably lived the life of a modern-day otter, eating small fish or invertebrates such as shrimp,” says Dr. David Whiteside, another supervisor. “These slender reptiles had long necks, a flattened tail for swimming, and remarkably robust forelimbs for a marine animal, suggesting that Pachystropheus may have come onto land to feed or avoid predators. Europe was shallow seas, and these animals may have lived in a large colony in the warm, shallow waters around the island archipelago.”

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

“We are delighted that this incredible fossil is now part of the collection at Bristol Museum & Art Gallery, thanks to the kind assistance of the Friends of Bristol Museums, Galleries & Archives.

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

Paper:

“The Relationships and Paleoecology of Pachystropheus rhaeticus, an Enigmatic Late Triassic Marine Reptile (Diapsida: Thalattosauria)” by Jacob G. Quinn, Evangelos Matheau-Raven, David I./. Whiteside, John EA Marshall, Deborah J. Hutchinson, and Michael J. Benton, in Journal of Vertebrate Paleontology.