Using CT scans and a new specimen, scientists have identified a prehistoric marine reptile found in 1935 as a thalattosaurus, not a choristodera. Reconstruction Pachystropheus rhaeticusfigured alongside a hybodont shark that feeds on a Birgeria Fish. Credit: James Ormiston
Scientists have reclassified a prehistoric marine reptile discovered in 1935 as one of the last thalattosaurs, not an early choristodera, following new findings and detailed imaging.
The true identity of a local prehistoric marine reptile has been revealed after experts discovered that some of its remains actually belonged to fish.
Scientists from the University of Bristol and the University of Southampton found that the bones found in Triassic rocks in 1935 came from one of the last thalattosaurs, a large sea lizard that behaved like an otter.
For years, the ancient animal was thought to be one of the first choristoderes, another group of crocodile-like marine reptiles. However, in a study published in Journal of Vertebrate Paleontologyteam examined the original named specimen from 1935. They compared it to a remarkable new specimen Pachystropheusknown as ‘Annie’, which contains hundreds of bones of several individuals, as well as evidence of sharks, bony fish and even land dinosaurs.
Advanced techniques and features
Jacob Quinn, who is studying a Masters in palaeobiology at Bristol’s School of Earth Sciences, traveled with two samples to Southampton where they were CT scanned and produced X-ray stacks through the blocks, allowing him to reconstruct a complete 3D model of everything buried within the blocks.
“Thalattosaurs existed throughout the Triassic,” explained Jacob. “Some of them were four meters long and would have been the terror of the seas. But ours Pachystropheus he was only a meter long and half of that was his long tail. It also had a long neck, a small head the size of a matchbox that we couldn’t find, and four paddles. If he were like his kin, he would have plenty of sharp teeth, ideal for catching fish and other small, squirming prey.”
Rhaetian (205 million years ago) Bristol Archipelago food web containing Pachystropheus rhaeticus. Arrows indicate who eats whom – red and black indicate inferred, and blue arrows are based on ecological and fossil associations observed during this study. Credit: Jacob Quinn
“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 proved that some of the bones were indeed from fish, and others that actually belonged to Pachystrophe show that it was actually a small thalattosaur. So, from being considered the first of the choristoderas, it is now identified as the last of the thalattosaurs.”
Discovery and reconstruction efforts
Evangelos R. Matheau-Raven of Peterborough discovered Annie while on holiday in Somerset in 2018 and then painstakingly pieced and cleaned her to reveal the bones in his spare time. He said: “I noticed parts of a fallen rock on the beach about 10 meters from the base of the cliff. I was excited when their exposed surfaces showed some fossil bones. It wasn’t until a few days later that I saw that the pieces collected two days in a row fit together. After a few weeks of preparation, we could see that something special was brewing. It took me about 350 hours and about a year to complete the sample.”
Evangelos R. Matheau-Raven during the preparation of ‘Annie’. Credit: Evangelos R. Matheau-Raven/Andrea Matheau-Raven
“Pachystropheus probably lived the life of a modern otter, ate small fish or invertebrates such as shrimp,” says Dr. David Whiteside, another leader. “These slender reptiles had long necks, a flattened tail for swimming, and remarkably robust forelimbs for a marine animal, suggesting Pachystropheus they may have come onto land to feed or avoid predators. At that time the Bristol area, and indeed much of Europe, was a shallow sea, and these animals could live in a large colony in the warm, shallow waters surrounding the island archipelago.’
Annie will now be housed at Bristol Museum & Art Gallery for further study.
“We are very pleased that this incredible fossil is now part of the collection at Bristol Museum & Art Gallery, thanks to the kind help of the friends of Bristol Museums, Galleries & Archives. We are excited to share the story of this new fossil and all the work the team has achieved with museum visitors,” says Bristol Museum & Art Gallery Curator of Geology, Deborah Hutchinson.
Reference: “Relationships and Paleoecology of Pachystropheus rhaeticus, an Enigmatic Latest Triassic Marine Reptile (Diapsida: Thalattosauria)” by Jacob G. Quinn, Evangelos R. Matheau-Raven, David I. Whiteside, John EA Marshall, Deborah J. Hutchinson, and Michael J. Benton, June 4, 2024, Journal of Vertebrate Paleontology.
DOI: 10.1080/02724634.2024.2350408