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Fossil of giant sea turtle discovered in Europe

Scientists estimate that the turtle would have been the size of an elephant and had characteristics unseen in other species of giant turtles.

(CN) — The largest living species of sea turtle, the leatherback, which can reach up to six feet long, would look tiny next to one of its ancient counterparts. Uncovered in northeastern Spain, the fossils of a portion of a giant prehistoric species of a turtle’s shell and pelvis are estimated to be twice the size of the leatherback turtle, making the discovery the largest marine turtle found in Europe.

Researchers presented the discovery of what has been dubbed Leviathanochelys aenigmatica in Scientific Reports on Thursday. Àngel Luján and colleagues estimate in the study that the turtle lived roughly 83 to 72 million years ago during the late Cretaceous period, alongside dinosaurs like the Tyrannosaurus Rex and the Triceratops.

The Leviathanochelys aenigmatica is the first evidence of marine turtles of the giant variety in Europe; other ancient species of turtles have been found in the region, but those did not exceed around five feet, matching the size of living sea turtle species.

Luján, a researcher with the Catalan Institute of Paleontology at the University of Barcelona in Spain and co-author of the paper said in an email interview, “Nowadays, marine turtles are reduced to 7 species, most of them being endangered. But in the past, they were much more diverse, both in shape and size. Giant marine turtles were especially common about 80 million years ago. But they became extinct 66 Ma, alongside dinosaurs, pterosaurs, and about 75% of the species of that time. However, despite their slow and leisurely appearance, turtles are true survivors. They have been on Earth for about 240 million years, surviving two of the most destructive mass extinctions.”

The study compared the Leviathanochelys aenigmatica to another extinct ancient turtle species, the Archelon. Specimens of gigantic sea turtles like the Archelon had previously only been found in North America, leading scientists to infer that the gigantism was contingent upon the Archelon’s living environment and location. The largest specimen of Archelon has been estimated to be 15 feet long and 6,400 pounds.

The Leviathanochelys aenigmatica, at a little over 12 feet long, roughly the height of an African elephant, is the second largest ancient marine turtle to be discovered and is uniquely the only one of these giant turtle species to be found in Europe.  The width of the turtle’s pelvis was estimated by the authors of the study to exceed even the width of the pelvis of Archelon.

The fossil was discovered in the Southern Pyrenees Mountains in 2016, with continuing excavation until 2021.

Aside from its massive size, researchers also documented differences in the pelvis of the turtle, whose fossil showed a protrusion at the front of the pelvis unseen in Archelon or in other giant turtle species.

“We speculate that this 'accessory process' served as an additional ankle point for muscles controlling the abdominal contraction. In turn, these muscles could participate in functions related to the respiratory system. For instance, some pelagic animals show a modification in their respiratory system intending to maximize their breathing capacity at high depths. Because of that, we suggest that Leviathanochelys could have a pelagic lifestyle,” Luján said.

The study concludes that the presence of a giant sea turtle in Europe indicates a previously undocumented biodiversity in marine turtles and sheds light on what leads to the phenomenon of megafauna in prehistoric animals.

“The finding of Leviathanochelys strongly suggests that gigantism in marine turtles was acquired independently, by different lineages over time,” authors of the study wrote. “However, it has been evidenced that the body size of extant marine turtles is related to a combination of environmental factors (i.e. predation pressure, competitive release, temperature) and their ecology (e.g. migration capacity, etc.).”

Luján also predicts that the Leviathanochelys aenigmatica is merely the first of many possible future discoveries of giant prehistoric marine turtles outside of North America.

“There is also evidence of large marine turtles in Northern Africa and Jordania from the same age as the newly described species. In fact, Southern Europe and North Africa shared several faunas, both marine and terrestrial, during the Late Cretaceous, between 80 and 66 million years ago. Because of that, it would be not surprising to discover new gigantic marine turtles in these regions.” Luján said.

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