Scientists have discovered the true identity of the ancient sea lizard

Researchers have identified a prehistoric marine reptile found in 1935 as a thalatosaurus, not a corystoder, using CT scans and a new specimen. Rebuilding Pachystropheus reticusemerged alongside a Hybodont shark feeding on a Bergeria Fish. Credit: James Ormiston

Scientists have reclassified the prehistoric marine reptile, which was discovered in 1935, as one of the last thalassosaurs, rather than the first dinosaurs, after new discoveries and detailed photography.

The true identity of a local prehistoric marine reptile has been revealed, after experts determined that some of its remains actually belonged to fish.

Researchers from the University of Bristol and the University of Southampton have proven that bones found in Triassic The rocks in 1935 are from one of the last thalassosaurs, a large marine lizard that behaved like an otter.

For years it was thought that this ancient animal was one of the first marine reptiles, another group of crocodile-like marine reptiles. However, in the study published in Journal of Vertebrate Paleontologythe team examined the original specimen bearing the name from 1935. They compared it to a remarkable new specimen from PachystropheusKnown as “Annie,” it contains hundreds of bones from several individuals, as well as evidence of sharks, bony fish and even terrestrial dinosaurs.

Advanced technologies and features

Jacob Quinn, who is studying for a master’s degree in paleobiology at Bristol School of Geosciences, traveled with the two specimens to Southampton where they were CT scanned, producing stacks of X-rays through the blocks that allowed him to reconstruct a full 3D model. For everything buried in blocks.

“Thalatosaurs existed throughout the Triassic,” Jacob explained. “Some were up to four meters (13 feet) long and would have been terrors of the seas. But we have them Pachystropheus It was only one meter long, half of which was its long tail. It also had a long neck, a small head the size of a matchbox, which we did not find, and four oars. If it had been like its relatives, it would have had lots of small, sharp teeth, perfect for snatching up fish and other small, squirming prey.

Rhaetian (205 million years ago) Food web of the Bristol Archipelago containing Pachystroeus rhaeticus. Arrows indicate who ate who – red and black mean inference, blue arrows are based on ecology and fossil associations observed during this study. Credit: Jacob Quinn

Professor Mike Benton, one of Jacob’s supervisors, said: ‘Previously, Pachystroeus was recognized as the first of the choristoderes, another group of crocodile-like marine reptiles, and was treated as very important because it was the oldest. “Jacob was able to prove that some of the bones actually came from fish, while other bones that really belonged to Pachystroeus showed that it was in fact a small thalattosaur. So, after being considered the first of the Christosaurs, it has now been identified as the last of the thalattosaurs.”

Discovery and reconstruction efforts

Evangelos R. Matthew Raven of Peterborough discovered the Annie while on holiday in Somerset in 2018, and subsequently carefully assembled and cleaned it to expose the bones in his spare time. He said: “I spotted parts of a fallen rock on the beach about 10 meters from the base of the cliff. I was thrilled that their exposed surfaces revealed some fossil bones. I wasn’t able to see the pieces put together until a few days later. After a few weeks of preparation, we were able to see something special emerge. The sample took about 350 hours and about a year to complete.

Evangelos R. Matto-Ravin during the preparation of the film “Annie”. Credit: Evangelos R. Matthew Raven/Andrea Matteo Raven

“Pachystropheus He may have lived the life of a modern day otter, eating small fish or… Invertebrates “Like shrimp,” says Dr. David Whiteside, another supervisor. “These slender reptiles had long necks, flat tails for swimming, and remarkably powerful forelimbs for a marine animal, suggesting Pachystropheus They may have come to land to feed or to avoid predators. At that time, Bristol, and most of Europe, were shallow seas, and these animals probably lived in a large colony in the warm, shallow waters surrounding the island archipelago.

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

“We are very pleased that this amazing fossil is now part of the collection at Bristol Museum and Art Gallery, thanks to the generous help of the Friends of Bristol Museums, Galleries and Archives. “We are delighted to be able to Sharing the story of this new fossil and all the work the team has accomplished with museum visitors.”

Reference: “Relationships and Paleoecology of Pachystroeus rhaeticus, the Most Enigmatic Triassic Marine Reptile (Diapsida: Thalattosauria)” by Jacob J. Quinn, and Evangelus R. Matto-Raven, and David I. Whiteside, and John E.E. Marshall, and Deborah J. Hutchinson and Michael J. Benton, June 4, 2024, Journal of Vertebrate Paleontology.
doi: 10.1080/02724634.2024.2350408