Scientific investigation into the mysterious holes of the largest T. rex fossil has yet to yield answers.

 On September 30, 2022, palaeontologist Jingmai O'Connor studied Sue's skull at the Field Museum in Chicago, U.S. Field Museum/Reuters.

Sue, the largest and best-preserved Tyrannosaurus rex yet found, was a terrible beast 67 million years ago in what is now South Dakota. Even this vast dinosaur, whose bones are in Chicago's Field Museum, was vulnerable. The set of round holes in Sue's jawbone is a perfect illustration of this phenomenon. Recent research has disproven a critical explanation about these holes, but a definitive answer remains elusive.

After examining Sue's left lower jawbone (mandible) in great detail, researchers concluded that the eight holes there (some the size of golf balls) were not caused by a microbial infection, as had been hypothesised by some specialists.

According to the study's principal author, Dr Bruce Rothschild, a research associate at the Carnegie Museum of Natural History in Pittsburgh, the holes are distinct from bone damage caused by such an infection. This week's Cretaceous Research published the findings.

Sue is one of the most famous dinosaur specimens, and she measures a whopping 12.3 metres (40-1/2 feet) in length. At the close of the Cretaceous Period, western North America was home to Tyrannosaurus rex, one of the largest terrestrial carnivores in history.

Field Museum palaeontologist Jingmai O'Connor says 15% of T. rex fossils have holes like Sue's.

The researchers looked into the possibility that protozoan infection caused the holes. Trichomoniasis is a protozoan infection that can infect humans and birds (evolved from dinosaurs with feathers) and is considered quite common. Trichomoniasis is sexually transmitted among humans but not among birds.

O'Connor said he saw damage in the jaw of one falcon with trichomoniasis, but it was different from the holes in Sue's teeth.

There was evidence of mending in the bone around Sue's wounds, suggesting that whatever caused them did not kill her. Sue's recovery mirrored that of other fossilised bones that had been broken and mended, as well as the bone mending around holes discovered in the skulls of ancient Inca people in Peru.

Sue's holes have yet to be explained.

The likelihood of claw damage during mating was first hypothesised by Rothschild, who described it as "mounting from back or top with claws striking the posterior mandible." Despite being given a female name in honour of the 1990s palaeontologist who uncovered the dinosaur's remains, Sue might have been either a male or a female.

"I honestly have no clue what formed them," O'Connor admitted. Those are not, in my opinion, bite or claw marks.

O'Connor remarked, "It's interesting that T. rex were susceptible to a disease that caused enormous holes to open up in the jawbone but just in the back of the jawbone, but didn't kill the T. rex because the holes started to heal, at least in Sue." "There have been numerous theories proposed that have been disproved. This is the type of palaeontology mystery that I enjoy the most."

Sue, a dinosaur who lived for roughly 33 years, wasn't just damaged by the holes; she also had a broken leg and tail.

O'Connor noted that Sue "shows multiple injuries and diseases," indicating that she was pretty old. "Its hands were aching from gout. Its ribs had been broken when it fell on its right side, but they eventually recovered. Ligament damage in the right arm was mending. A severe bone infection crippled the animal's left leg. Its tail was aching from arthritis. The animal probably wasn't too content in its final year."