One of the world's most famous dinosaurs — Sue, the T. rex at the Field Museum in Chicago — died of a parasitic infection, not in a fight with another dinosaur, researchers say.

The fossilized remains of the tyrannosaurus rex, the star attraction of the Chicago museum, has a series of marks on the jaw that some paleontologists have attributed to a fight with another dinosaur, possibly another T. rex.

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This reconstruction of the trichomonosis infection in a T. rex shows lesions in the jaw that penetrate to the bone. ((Chris Glen/University of Queensland))

A team of American and Australian researchers now says the lesions on the jawbones of Sue and nine other T. rex specimens are the result of a parasitic infection, called trichomonosis, that infects modern birds.

The study, led by Ewan Wolff of the University of Wisconsin-Madison and Steven Salisbury of the University of Queensland, compared the holes on the dinosaurs' skulls to similar scars that appear on the beaks of infected birds.

"What drew my attention to trichomonosis as a potential candidate for these mysterious lesions on the jaws of tyrannosaurs is the manifestation of the effects of the disease in [birds of prey]," Wolff said in a statement.

"When we started looking at trichomonosis in greater depth, there was a story that matched some lines of evidence for transmission of the disease in tyrannosaurs."

In birds, the single-celled parasite Trichomonas gallina can be transmitted from birds such as pigeons to birds of prey, such as falcons and hawks. Pigeons are carriers for the parasite and don't suffer any symptoms, but the birds of prey can get lesions on their beaks.

CBC Radio's Quirks and Quarks will have an interview with study lead author Ewan Wolff Oct. 17 at noon.

Wolff said the pattern of lesions seen in birds closely matches the holes found on some T. rex skulls. The research appears in the online journal Public Library of Science One.

What's more, the holes in the jaws were neat and had smooth edges, while marks from bites, seen on other dinosaur skeletons, are ragged and messy, Wolff said.

The parasitic infection in the dinosaur's mouth and throat could have been so severe that it led to its death.

"The lesions we observe on Sue suggest a very advanced stage of the disease and may even have been the cause of her demise,"  Wolff said.

"It's ironic to think that an animal as mighty as 'Sue' probably died as a result of a parasitic infection," Salisbury said. "I'll never look at a feral pigeon the same way again."

Because there's no evidence of trichomonosis in other dinosaur species, Wolff said the parasite would have been passed from one T. rex to another, most likely through saliva or by cannibalism.

"Fighting and specifically head-biting would have been an ideal mechanism for spreading the disease among tyrannosaurs," said Salisbury.