Did Tyrannosaurus Rex Die from Bird Disease?

Deadly Avian Parasites may Have Defeated the Mightiest Dinosaurs

Oct 12, 2009 Sue Cartledge

The world's largest and fiercest dinosaur, Tyrannosaurus rex, might have been wiped out by parasites similar to those found in feral pigeons, a new study shows.

Australian palaeontologist Dr Steve Salisbury, and American colleagues Ewan Wolff, from the University of Wisconsin-Madison, and Jack Horner and David Varricchio, from Montana State University, have found that Tyrannosaurus rex and its close relatives suffered from a deadly infectious disease similar to one that occurs in birds today.

The disease, trichomonosis, is caused by a parasite and is most prevalent in pigeons, both feral and domestic, which are generally immune to it.

“Birds of prey are particularly susceptible to trichomonosis if they eat infected pigeons,” Dr Salisbury said.

“Adult birds can then pass the disease to their nestlings through beak-to-beak contact.”

Holes in T. rex Skulls Clue to the Disease

Dr Salisbury said the clue to the parasitic infection came from unnatural holes seen in the in the back of the dinosaurs’ lower jaws.

“Some of the world's most famous T. rex specimens have these holes in their jaws, including ‘Sue' at the Field Museum in Chicago,” he said.

He said tyrannosaurs were known to have marks on their heads from biting each other, presumably during territorial disputes or mating, but the holes he and his colleagues were interested too far back in the lower jaws to be bite marks.

The researchers conducted an extensive survey of tyrannosaur specimens in American museums and identified ten individuals with full-thickness erosive lesions (holes). These lesions were described, measured and photographed for comparison with one another.

The holes were described in their study as “multiple, smooth-edged full-thickness erosive lesions on the mandible, either unilaterally or bilaterally.

“The cause of these lesions in the Tyrannosaurus rex specimen FMNH PR2081 (‘Sue’) has previously been attributed to actinomycosis, a bacterial bone infection, or bite wounds from other tyrannosaurids,” the researchers reported.

Dr Salisbury said that dinosaur fossils often display evidence of injuries that could be attributed to accidents, old age or metabolic disorders. "Among predatory dinosaurs, the most commonly encountered abnormalities are bite-marks and related bone traumas on the head."

However, after considering all the evidence, the researchers dismissed these explanations for the large holes.

“These holes don't show any of the normal characteristics of bite marks,” Dr Salisbury explained.“It's as if someone took to the jaws with a hot poker. Some specimens look like Swiss cheese.”

T. rex 'Sue' Killed by Pigeon Disease

Most commonly found in feral pigeons, who are immune to the parasite, trichomonosis can be deadly to other birds, especially birds of prey – and tyrannosaurs

"As the parasite takes hold, lesions form around the jaw and inside the throat, eventually eating away the bone,” Dr Salisbury said.

“As the lesions grow, the animal has trouble swallowing food and eventually starves to death.

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

The study was published in the online scientific journal PLoS ONE.

Bird Disease Indicates Evolution of Dinosaur Immune System

Dr Salisbury said the fact that T. rex suffered from an avian parasite was not surprising, “given the evolutionary relationship of dinosaurs to birds, but the discovery of a likely candidate for such a disease link represents a major step forward in our understanding of disease history in birds and their dinosaurian precursors.”

“This finding not only establishes that some non-avian theropods had a similar infectious disease to that found in living birds, but also suggests a similar or common immune response to the disease.

“The symptoms seen in tyrannosaurs indicate that their immune response to the disease is almost identical to that found in living birds,” he said

Dinosaur Disease Spread by Biting

As the tyrannosaurs appeared to be the only dinosaurs affected by the trichomonosis-like parasite, the researchers hypothesised that it was spread by biting as the dinosaurs fought each other.

Although some of the animals could have been infected by eating infected prey, or drinking contaminated water, the researchers believed that the disease spreading only between members of the tyrannosaur family suggested the infection was spread through bites on the face and head.

“We don't think it is a coincidence that a significant number of adult tyrannosaur specimens show both face-biting marks and evidence of a trichomonosis-like disease,” Dr Salisbury said.

“Fighting and specifically head-biting would have been an ideal mechanism for spreading the disease among tyrannosaurs.

“We can see similarities with what has been happening to Tasmanian devils recently, where a malignant and debilitating oral cancer is being spread by animals fighting and biting each other's faces.”

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The copyright of the article Did Tyrannosaurus Rex Die from Bird Disease? in Paleontology is owned by Sue Cartledge. Permission to republish Did Tyrannosaurus Rex Die from Bird Disease? in print or online must be granted by the author in writing.

Painting of a T Rex Head, Showing Infected Lesions

Reconstructed T Rex Skull with Trichomonas Holes