Megan Jacobs/University of Portsmouth
The artwork by study co-author Megan Jacobs imagines what a large pliosaur would have looked like in the late Jurassic period.
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The potential discovery of large fossil specimens in a museum staircase has led researchers to conclude that giant marine reptiles called pliosaurs roamed the seas 152 million years ago, according to a recent study.
Findings from the late Jurassic period, though fragmentary, suggest that pliosaurs were twice the size of the killer whale — and lead study author David Martell comes close to salvation. This is due to what many researchers consider to be inaccurate claims he made about the size of another pliosaur in the 1999 BBC TV documentary series Walking with Dinosaurs.
One episode showed “Liopleurodon 25 meters long”, which “provoked heated debates…as it was thought to have been grossly overestimated and likely only reached an adult size of just over six meters in length”, according to toa news releaseset current study, which was published May 10 in Proceedings of the Geologists Association.
Martell, who was a consultant for the episode and is now a professor in the School of Environment, Geography and Earth Sciences at the University of Portsmouth in the UK, said he got the size “very wrong”.
“I based my calculations on some fragmentary material indicating that Liopleurodon could grow to 25 meters in length, but the evidence was scant and caused a lot of controversy at the time,” he said in a statement. “Now we have some more reliable evidence after the coincidental discovery of four massive (vertebrae).”
Martel recently found one of those vertebrae in a drawer of fossils at the Abingdon County Hall Museum in England, and later learned that the curator had three more in storage. The vertebrae were large, with a maximum width of 269 mm (10.5 in), a maximum height of 222 mm (8.7 in) and a maximum length of 103 mm (4 in).
Given the size of the vertebrae and comparisons with other fossils of other mid-Jurassic and early Cretaceous species, the researchers concluded that they were closely related to pliosaurs or similar but undescribed species, according to the study.
A topographic survey showed that the reptile had grown to between 9.8 and 14.4 meters (roughly 32 to 47 feet long), the authors write.
Martell added, “While it’s not yet on par with the claims made for Liopleurodon in the popular TV series ‘Walking with Dinosaurs,’ it wouldn’t surprise me if we someday found clear evidence that this feral species was even larger.”
Adam S. agreed. Smith, Curator of Natural Sciences at Nottingham Museum of Natural History, Wollaton Hall, agrees.
It is not possible that the length of the pliosaurs exceeded 15 meters. Smith said via email. However, he cautioned that the increase in length corresponded to an “exponential increase in size … a biological limit could be placed on the size of larger pliosaurs”. Smith was not involved in the study.
Pliosaurs were “a group of large, carnivorous marine reptiles characterized by massive heads, short necks, and streamlined, teardrop-shaped bodies.” According to Britannica. Four large flippers helped propel the ancient creatures across the seas. Pliosaurs were similar to plesiosaurs, their relatives in the order Plesiosauria, but they had elongated heads and shorter necks.
“We know that these pliosaurs were very fearsome animals that swam in the seas that covered Oxfordshire 145-152 million years ago,” Martell said. “They had a huge skull with huge protruding teeth like daggers – as big, if not bigger, than a T-Rex, and certainly more powerful.
“They were at the top of the marine food chain and may have preyed on ichthyosaurs, long-necked plesiosaurs and possibly even smaller marine crocodiles, simply by biting them in half and removing pieces from them,” he added. “We know they were butchering smaller marine reptiles because you can see bite marks in the ichthyosaur bones in the examples on display in The Etches Collection in Dorset.”
Valentine Fisher Professor in the Department of Geology at University of Liège who was not part of the study, called the results “shaky” because the lengths of the cervical vertebrae — the type the authors analyzed — of pliosaurs could vary.
However, another expert believes that estimates aren’t necessarily a bad thing.
“A measurement is always based on a best guess using the specimens that we know about,” Andrew Cove, a UK-based paleontologist who was not involved in the study, said via email. “The author in this present study appears to have done a good job of comparing specimens and attempting to extend the range of more complete fossil individuals so that the newly described vertebrae would fit in. Whether 14.4 meters in length is realistic or perhaps very large will require more complete specimens to confirm with certainty, But I wouldn’t be surprised if pliosaurs of this size swam in the Jurassic seas.”
The vertebrae were initially found during excavations at Warren Farm in the Thames River Valley near Abingdon in Oxfordshire, and are derived from the Kimmeridge Clay Formation, according to the study.
“This kind of discovery reminds us that there were some amazing animals in the past,” Michael Benton, a professor of vertebrate paleontology at the University of Bristol in the UK, said via email. Benton was not involved in the study. “Here is a marine reptile the size of a sperm whale, and there is nothing like it today.”
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