Formally known as FMNH PR2081, Sue is the largest and best-preserved T. rex specimen in the world. Although scientists know a lot about Sue, whose skeleton currently resides at the Field Museum in Chicago, they still puzzle over what caused the smooth-edged holes in her jaw. (She’s named Sue even though her sex is one of her mysteries.)
Possible explanations for the damage, which has been found in several other specimens’ skulls as well, have included bite wounds and fungal infections, but these culprits don’t match well with the holes’ shapes, sizes and locations, says study coauthor Ewan Wolff of the University of Wisconsin–Madison.
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Wolff and his colleagues turned to diseased birds and crocodiles to get a hint about what might have afflicted these T. rex. Wolff found an osprey skull with holes similar to those seen in some of the dinosaur specimens. While it was living, the osprey had been infected with a species of Trichomonas, so the researchers focused on this nasty parasite. Trichomonas commonly infects pigeons, turkeys, chickens and raptors to varying degrees. In severe cases, Trichomonas can cause a filmy infection site to form at the back of the mandible, preventing the animal from eating and drinking. The infection also causes the jaw to rot and leaves visible holes.
Wolff, along with Steven Salisbury, John Horner and David Varricchio, analyzed the skulls of 61 T. rex specimens and found nine (including Sue) with lesions similar to those caused by Trichomonas. The smoothness and location of the holes were similar in the dinosaurs and in infected birds. “Either this was a fantastic coincidence, or this was a very common disease in T. rex,” Wolff says.
Infectious debris that becomes chronically inflamed can ultimately close off the throat. Such an infection may have led Sue to starve, Wolff says. “There are some things you can survive,” Wolff says, “but not having a hole in the back of your throat is not one of them.”
Researchers don’t know how the disease may have been transmitted among dinosaurs. Raptors catch the parasite from eating infected prey, but so far, scientists haven’t found any evidence of infected T. rex meals, Wolff says. “We have lots to look at, but so far, we’re not finding this disease.” The dinosaurs might have also transmitted the disease through face biting and cannibalism, Wolff says.
The new study is very interesting because “it supports our view that dinosaurs were infected by many pathogens,” says paleobiologist George Poinar of Oregon State University in Corvallis. “I think more people will be looking for this now.”