Researchers identified a prehistoric marine reptile found in 1935 as a thalattosaur and not a choristodere based on CT scans and a new specimen. Reconstruction of Pachystropheus rhaeticuspictured next to a hybodont shark feeding on a Birgeria Fish. Photo credit: James Ormiston
Based on new findings and detailed images, scientists have reclassified a prehistoric marine reptile discovered in 1935, no longer as an early choristodere, but as one of the last thalattosaurs.
The true identity of a native prehistoric marine reptile has been revealed after experts determined that some of its remains actually came from fish.
Researchers from the Universities of Bristol and Southampton have found that bones in Triassic The rocks, dated 1935, come from one of the last thalattosaurs, a large sea lizard that behaved like an otter.
For years it was assumed that the prehistoric animal belonged to the first Choristoderes, another group of crocodile-like marine reptiles. In the study, which was published in Journal of Vertebrate PalaeontologyThe team examined the original eponymous specimen from 1935. They compared it with a remarkable new specimen from Pachystropheusknown as “Annie”, contains hundreds of bones from various individuals as well as evidence of the existence of sharks, bony fish and even land dinosaurs.
Advanced techniques and features
Jacob Quinn, who is studying for a Masters in Palaeobiology at the School of Earth Sciences in Bristol, took the two specimens to Southampton where they underwent CT scanning, which involved passing numerous X-rays through the blocks so he could reconstruct a complete 3D model of everything buried in the blocks.
“Thalattosaurs existed throughout the Triassic period,” Jacob explained. “Some of them reached a length of four meters and were the terror of the seas. But our Pachystropheus was only a meter long, and half of that was its long tail. It also had a long neck, a small head the size of a matchbox, which we had not found, and four paddles. If it had been like its relatives, it would have had many sharp little teeth, ideal for catching fish and other small, wriggling prey.”
Rhaetian (205 million years ago) food web of the Bristol Archipelago with Pachystropheus rhaeticus. Arrows indicate who eats whom – red and black mean inferred, and blue arrows are based on ecology and fossil associations observed during this study. Image credit: Jacob Quinn
“Pachystropheus had previously been identified as the first of the Choristoderes, another group of crocodile-like marine reptiles, and it was considered 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 were actually fish, and the others that really belonged to Pachystropheus show that it was actually a small thalattosaur. So it was no longer considered the first of the Choristoderes, but is now identified as the last of the thalattosaurs.”
Discovery and reconstruction efforts
Evangelos R. Matheau-Raven from Peterborough discovered Annie in 2018 while on holiday in Somerset and then painstakingly reassembled and cleaned her in his spare time to expose the bones. He said: “I discovered pieces of a fallen rock on the beach, about 10m from the base of the cliff. I was delighted when their exposed surfaces revealed some fossil bones. It was only a few days later that I could see that the pieces, collected two days apart, fit together. After a few weeks of preparation, we could see that something special was emerging. It took me about 350 hours and about a year to complete the specimen.”
Evangelos R. Matheau-Raven preparing for “Annie”. Photo credit: Evangelos R. Matheau-Raven/Andrea Matheau-Raven
“Pachystropheus probably lived the life of a modern otter and ate small fish or Invertebrates like shrimps,” says Dr. David Whiteside, another supervisor. “These slender reptiles had long necks, a tail flattened for swimming, and remarkably robust forelimbs for a marine animal, suggesting Pachystropheus “They may have come ashore to find food or to escape predators. At that time, the sea in the Bristol area and much of Europe was shallow, 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 the Bristol Museum & Art Gallery for further studies.
“We are delighted that this incredible fossil is now part of the Bristol Museum & Art Gallery collection, thanks to the kind support of the Friends of Bristol Museums, Galleries & Archives. We look forward to sharing 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 & Art Gallery.
Reference: “The relationships and paleoecology of Pachystropheus rhaeticus, an enigmatic marine reptile from the latest Triassic (Diapsida: Thalattosauria)” by Jacob G. Quinn, Evangelos R. Matheau-Raven, David I. Whiteside, John EA Marshall, Deborah J. Hutchinson, and Michael J. Benton, 4 June 2024, Journal of Vertebrate Palaeontology.
DOI: 10.1080/02724634.2024.2350408