Pliosaurs were larger much earlier than previously thought

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Pliosaurs, a subset within the plesiosaur group, were found to attain remarkable sizes far earlier than previously believed, as indicated by research conducted by an international team, including a scientist affiliated with the Polish Academy of Sciences. This discovery provides new insights into the evolutionary trajectory of these formidable oceanic predators.

Pliosaurs, a category of ancient marine reptiles, emerged around the transition from the Triassic to the Jurassic period, approximately 200 million years ago, and vanished during the early Late Cretaceous, about 90 million years ago.

These creatures inhabited diverse regions across the globe. Renowned examples like Liopleurodon, Pliosaurus, and Kronosaurus were recognized for their expansive skulls, robust teeth, limited neck length, and considerable body sizes, occasionally surpassing lengths of 10 meters. They were part of the evolutionary lineage of plesiosaurs, dominating the seas and oceans throughout the Mesozoic era, akin to the role played by dinosaurs on land.

“At some point in their evolutionary history, pliosaurs became quite large and have since taken over marine ecosystems, becoming apex predators in Mesozoic seas. However, until now we did not know when it happened,” said one of the co-authors of the article, Dr. Daniel Madzia from the Institute of Paleobiology of the Polish Academy of Sciences, in an interview with Nauka w Polsce.

The revelation stemmed from an examination of fossils unearthed in 1983 close to Metz, France. These findings comprised a colossal lower jaw, measuring 1.3 meters in length, belonging to a pliosaur estimated to be roughly 6 meters long. Additionally, remnants of the upper jaw, teeth, and various postcranial skeletal bones from this particular specimen were also recovered and preserved.

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“In the 1990s, it was described as a new species: Simolestes keileni. However, it was forgotten about quite quickly. We re-examined this specimen and found that it is the oldest known representative of the pliosaur group with large skulls, short necks and a massive body structure, and is approximately 170 million years old. Thus, we included it in a new genus, which we named Lorrainosaurus, and extended the evolutionary line of short-necked pliosaurs, proving that they reached their great size about 5 million years earlier than previously thought,” explained the palaeontologist.

The emergence of formidable pliosaurs coincided with significant shifts in the makeup of the expansive marine vertebrate fauna, encompassing plesiosaurs, ichthyosaurs, and aquatic relatives of crocodiles. Consequently, pliosaurs assumed the position of top-tier marine predators, a role previously occupied by other sizable carnivorous plesiosaurs known as romaleosaurs, more than 175 million years ago.

Initially, however, it is probable that large, short-necked pliosaurs like Lorrainosaurus consumed different prey, as indicated by an analysis of the reptiles’ dental structure. Subsequently, for reasons yet to be determined, romaleosaurs began to relinquish their predominant status.

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