New Evidence Suggests Enormous Pliosaurs Swam in Late Jurassic Seas, Dwarfing Killer Whales

by Manuel Costa

Caption for the artist’s impression: An artist’s depiction of a pliosaur. Credit: Megan Jacobs, University of Portsmouth

Over twenty years ago, the BBC’s documentary series “Walking with Dinosaurs” featured a controversial portrayal of a 25-meter-long Liopleurodon, sparking heated debates about the true size of this pliosaur. The depiction was widely criticized as overly exaggerated, with the prevailing belief suggesting that an adult Liopleurodon would have measured slightly over six meters.

While speculation on the subject was expected to continue, a remarkable discovery in an Oxfordshire museum has prompted paleontologists from the University of Portsmouth to publish a research paper proposing that a related species could reach an astonishing length of 14.4 meters, twice the size of a killer whale.

Professor David Martill, from the University of Portsmouth’s School of the Environment, Geography, and Geosciences, stated, “As a consultant for the BBC’s pilot program ‘Cruel Sea,’ I must admit that I greatly miscalculated the size of Liopleurodon. My calculations were based on fragmentary evidence that suggested a maximum length of 25 meters, but the evidence was scarce and it sparked significant controversy at the time.”

“The size estimation presented by the BBC in 1999 was exaggerated. However, we now possess much more reliable evidence following the fortuitous discovery of four enormous vertebrates,” Professor Martill added.

Megan Jacobs, Professor Martill’s co-author, stumbled upon the vertebrae while photographing an ichthyosaur skeleton at Abingdon County Hall Museum. As Professor Martill examined fossil-filled drawers, he was delighted to find a large vertebra and soon discovered that the curator had three more in storage.

The vertebrae bear distinct resemblances to those of a Pliosaurus species or a similar creature. Pliosaurs, resembling plesiosaurs but with elongated heads akin to crocodiles and shorter necks, possessed four flippers that functioned as powerful paddles, propelling them through the water, alongside a relatively short tail.

After conducting topographic scans, Professor Martill and his colleagues calculated that this Late Jurassic marine reptile could have measured anywhere between 9.8 and 14.4 meters in length.

“We know these pliosaurs were formidable creatures that inhabited the seas covering Oxfordshire 145-152 million years ago. They possessed massive skulls with enormous teeth resembling daggers—some as large, if not larger, than those of a T. rex—and certainly more powerful,” he explained.

“They occupied the top position in the marine food chain, likely preying on ichthyosaurs, long-necked plesiosaurs, and perhaps even smaller marine crocodiles, effortlessly tearing them apart and devouring them. Evidence of their predatory behavior can be seen in the bite marks found on ichthyosaur bones displayed at The Etches Collection in Dorset,” Professor Martill continued.

The vertebrae were initially unearthed during temporary excavations at Warren Farm in the River Thames Valley, Oxfordshire, and originate from the Kimmeridge Clay Formation, a deposit dating back 152 million years to the Late Jurassic period.

Professor Martill concluded by saying, “It is thrilling to confirm the existence of a genuinely colossal pliosaur species in the Late Jurassic seas. Although not yet reaching the proportions attributed to Liopleurodon in the iconic BBC TV series ‘Walking with Dinosaurs,’ it would not surprise me if, one day, we uncover definitive evidence indicating that this monstrous species was even larger.”

Reference: “A truly gigantic pliosaur (Reptilia, Sauropterygia) from the Kimmeridge Clay Formation (Upper Jurassic, Kimmeridgian) of England” by David M. Martill, Megan L. Jacobs, and Roy E. Smith, 10 May 2023, Proceedings of the Geologists’ Association.
DOI: 10.1016/j.pgeola.2023.04.005

Frequently Asked Questions (FAQs) about pliosaurs

What is the new evidence regarding pliosaurs in Late Jurassic seas?

The new evidence suggests that pliosaurs in Late Jurassic seas could reach a length of 14.4 meters, twice the size of a killer whale. This challenges previous size estimations and provides a more accurate understanding of these ancient marine reptiles.

How was the new evidence discovered?

The evidence was discovered serendipitously in an Oxfordshire museum. While photographing an ichthyosaur skeleton, a researcher found large vertebrae closely related to a Pliosaurus species. Further investigation revealed three more vertebrae in storage, leading to the realization of the enormous size potential of these pliosaurs.

What were pliosaurs like?

Pliosaurs were marine reptiles resembling plesiosaurs but with elongated heads similar to crocodiles and shorter necks. They had four flippers, which acted as powerful paddles, and a relatively short tail. Their massive skulls featured huge protruding teeth, making them formidable predators at the top of the Late Jurassic marine food chain.

How were smaller marine reptiles preyed upon by pliosaurs?

Pliosaurs likely preyed on smaller marine reptiles, including ichthyosaurs, long-necked plesiosaurs, and possibly even smaller marine crocodiles. They would bite their prey in half and consume chunks of their bodies. Bite marks on ichthyosaur bones found in exhibits at The Etches Collection in Dorset provide evidence of their predatory behavior.

What is the significance of this discovery?

This discovery confirms the existence of a truly gigantic pliosaur species in Late Jurassic seas and challenges previous size estimations. While not yet matching the proportions attributed to Liopleurodon in the famous BBC TV series “Walking with Dinosaurs,” further evidence may reveal even larger specimens in the future, expanding our understanding of these ancient creatures.

More about pliosaurs

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PrehistoricExplorer July 11, 2023 - 6:11 pm

wow, this is mind-blowing! I’ve always been fascinated by pliosaurs, and this new evidence is just incredible. It’s so cool that they found those vertebrae in a museum. Can you imagine how massive these creatures must have been? Nature never ceases to amaze me!

DinoFan87 July 11, 2023 - 6:17 pm

omg! i luv pliosaurz! they rly big and scary. i saw that doc on tv, and they said they was super big but then ppl said no they not. now they found bones that say they cud b even BIGGER! that’s amazin! i wanna see 1 in real life!

FossilHunter123 July 11, 2023 - 7:01 pm

Finally, some solid evidence to support the larger size of pliosaurs! I remember all the arguments and debates about the size of Liopleurodon. Looks like the BBC got it wrong, but now we have these vertebrae to back up the claims. Can’t wait to learn more about these ancient marine giants!


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