"The most exciting aspect of this research for me is the arthritic condition, which has never been seen before in these or similar Mesozoic reptiles," researcher Judyth Sassoon at the University of Bristol told LiveScience.
The degenerative condition had eroded the pliosaur's left jaw joint. This would have knocked its lower jaw askew.
"In the same way that aging humans develop arthritic hips, this old lady developed an arthritic jaw and survived with her disability for some time," Sassoon said. "But an unhealed fracture on the jaw indicates that at some time the jaw weakened and eventually broke.
"With a broken jaw, the pliosaur would not have been able to feed, and that final accident probably led to her demise."
Marks on the lower jawbone from the pliosaur's upper teeth suggest the predator lived with a crooked jaw for many years, long enough to damage its own bones.
"You can see these kinds of deformities in living animals, such as crocodiles or sperm whales, and these animals can survive for years as long as they are still able to feed. But it must be painful," Benton said. "Remember that the fictional whale Moby-Dick, from Herman Melville's novel, was supposed to have had a crooked jaw." (Album: World's Biggest Beasts)