Researchers have identified a prehistoric marine reptile found in 1935 as a thalattosaur, not a coristodere, using CT scans and a new specimen. The reconstruction of Pachystropheus rhaeticuspictured together with a hybodont shark feeding on a Brewery the fish. Credit: James Ormiston
Scientists have reclassified a prehistoric marine reptile discovered in 1935 as one of the last thalattosaurs, not an early coristodere, following new findings and detailed imaging.
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 the bones found in Triassic the rocks in 1935 are from one of the last thalattosaurs, a large sea lizard that behaved like an otter.
For years it was assumed that the ancient animal was one of the first choristoderes, another group of crocodile-like marine reptiles. However, in the study published in Journal of Vertebrate Paleontologyteam examined the original named specimen from 1935. They compared this to a striking new specimen of Pachystropheusknown as ‘Annie’, containing hundreds of bones from several individuals, as well as evidence of sharks, bony fish and even land dinosaurs.
Advanced techniques and features
Jacob Quinn, who is studying for his Masters in Palaeobiology at the Bristol School of Earth Sciences, traveled with the two specimens to Southampton where they were CT-scanned, producing beams of X-rays through the blocks that allowed him to reconstruct a model of full 3D of everything buried in blocks.
“Thalattosaurs existed throughout the Triassic,” explained Jacob. “Some of them reached four meters (13 feet) in length and would be the terrors of the seas. But ours Pachystropheus it was only a meter long and half of it was its long tail. It also had a long neck, a head as small as a matchbox, which we had not found, and four shovels. If it was like its relatives, it would have lots of sharp little teeth, ideal for grabbing fish and other small, squishy prey.”
The Rhaetian (205 million years ago) food web of the Bristol Archipelago containing Pachystropheus rhaeticus. Arrows indicate who eats who – red and black mean inferred, and blue arrows are based on ecology and fossil relationships observed during this study. Credit: Jacob Quinn
“Pachystropheus had previously been 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 others that really belonged to Pachystropheus show that it was actually a small thalattosaur. So, considered to be 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 he carefully pieced it together and cleaned it to expose the bones in his spare time. He said: “I saw pieces of a rock fall on the beach about 10 meters from the base of the cliff. I was excited as their exposed surfaces showed some fossil bones. It wasn’t until a few days later that I could see that the pieces assembled two days apart fit together. After a few weeks of preparation, we could see that something special was emerging. The sample took me about 350 hours and about a year to complete.
Evangelos R. Matheau-Raven during the making of ‘Annie’. Credit: Evangelos R. Matheau-Raven/Andrea Matheau-Raven
“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 unusually strong forelimbs for a marine animal, suggesting Pachystropheus it may have come to land to feed or to avoid predators. At the time, the Bristol area, and indeed most of Europe, were shallow seas, and these animals may have lived in a large colony in the warm, shallow waters surrounding the island archipelago.
Annie will now be housed at Bristol Museum and Art Gallery for further study.
“We are very pleased that this remarkable fossil is now part of the collection at Bristol Museum and Art Gallery, thanks to the kind help of the Friends of Bristol Museums, Galleries and Archives. We are thrilled to be able to share the story of this new fossil and all the work the team has achieved with museum visitors,” says Bristol Museum and Art Gallery’s 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 Hutch. Michael J. Benton, June 4, 2024, Journal of Vertebrate Paleontology.
DOI: 10.1080/02724634.2024.2350408