For several decades, Liopleurodon ferox — a short-necked marine reptile that patrolled the seas of what is now England and France some 163 million years ago — has held a reputation as one of the largest predators to ever swim the oceans, with some estimates putting its length at a jaw-dropping 25 m. By re-examining every known specimen of Liopleurodon ferox, paleontologists at the University of Portsmouth found that the species was far shorter, but its massive skull still made it a fearsome apex predator.
An artist’s impression of a pliosaur. Image credit: Megan Jacobs, University of Portsmouth.
“Liopleurodon ferox is a well-known thalassophonean pliosaurid from the Middle Jurassic (Callovian) Oxford Clay Formation of England and equivalent strata in northwest France,” said University of Portsmouth paleontologist Edward Bartlett and his colleagues.
“It is among the earliest of thalassophoneans to be known from near-complete skeletons.”
“Consequently, Liopleurodon ferox has become a benchmark for systematic studies and size comparisons of thalassophoneans. However, a complicated taxonomic history stemming from the diagnosis of the holotype, an isolated caniniform tooth originally described in 1873, has led to the referral of many Callovian-Tithonian pliosaurid specimens to the genus.”
“This has resulted in a wide range of size estimates from 6.39 m to the astonishing 25 m presented in the 1999 BBC TV series Walking with Dinosaurs.”
In their research, Dr. Bartlett and co-authors analyzed 37 specimens attributed to Liopleurodon ferox.
They calculated a total body length ranging from about 2.46 to 8.09 m, with the more complete skeletons clustering around 4.8 to roughly 6 m.
The average animal, they concluded, was likely close to 5 m long — still a fearsome predator, but a fraction of the mythical 25-m figure.
“Our study is the first comprehensive reappraisal of every specimen assigned to Liopleurodon ferox,” Dr. Bartlett said.
“By bringing together all of the available material, we can finally provide a robust estimate of its size and body proportions.”
“Although it was smaller than some famous reconstructions, it was still the dominant marine predator in the Jurassic Oxford Clay seas.”
To build their revised model, the paleontologists turned to two well-preserved skeletons — one housed in Tübingen, Germany, and another at the Natural History Museum in London — along with a separate, complete skull used to calibrate cranial proportions.
They found that the skull makes up about 24% of the animal’s skeletal length, a notably larger share than earlier estimates suggested, hinting that Liopleurodon ferox could tackle relatively large prey compared with other pliosaurs living alongside it.
Even scaled down, Liopleurodon ferox remains the largest known animal from the Oxford Clay Formation ecosystem.
“Our study is the first comprehensive reappraisal of every specimen assigned to Liopleurodon ferox,” Dr. Bartlett said.
“By bringing together all of the available material, we can finally provide a robust estimate of its size and body proportions.”
But the researchers also flag something more surprising: several fragmentary fossils from the same rock formation appear to belong to pliosaurs considerably larger than any confirmed Liopleurodon ferox, with estimated lengths reaching as high as 12.2 m.
Because these specimens lack the diagnostic features needed to assign them to a species, their identity remains a mystery, though they suggest that true giants were swimming in Middle Jurassic seas alongside Liopleurodon ferox.
“Indeterminate Oxford Clay Formation pliosaurid specimens estimated at 7.02-12.2 m total body length demonstrate that gigantism in pliosaurs (over 10 m) evolved during the late Middle Jurassic,” the scientists said.
The findings appear in the Journal of Vertebrate Palaeontology.
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Edward O. Bartlett et al. Re-evaluating body size in the Middle Jurassic pliosaur Liopleurodon ferox Sauvage, 1873. Journal of Vertebrate Paleontology, published online July 16, 2026; doi: 10.1080/02724634.2026.2691149
